A.B. is a 40 a old female patient complaining of kidney stones. Microscopic examination of urine reveals hexagonal crystals. Elemental analysis shows that the crystals are made of a compound that contains sulphur. Family history reveals an autosomal recessive inheritance. The patient should NOT be treated by:

agents that increase urine pH (e.g. penicillamine)

A 2-week-old infant presents with vomiting, lethargy and convulsions without evidence of an infectious process. Laboratory examination reveals hyperammonemia with alkalosis. Glutamine, citrulline and arginine are found elevated in the blood. The enzyme that is most likely deficient in this patient is:

Carbamoyl-phosphate synthetase I

A nurse notices that the urine produced by a newborn infant has the odor of maple syrup. Which of the following pathways is most likely defective?

Metabolism of branched-chain amino acids

Metabolism of aromatic amino acids

Metabolism of sulfur-containing amino acids

Transformation of carbohydrates to amino acids

A patient reports to you that he has had aches and pains in his muscles for the past seven days. A blood test shows increased levels of creatine kinase MM, fatty acids and also myoglobin. A second blood sample, this time taken after an overnight fast, revealed low levels of blood glucose and elevated very low density lipoprotein (VLDL). This patient most likely has which of the following conditions?

Carnitine acyltranferase deficiency

Essential amino acid deficiency

Type 1 glycogen storage disease

Carnitine acyltranferase deficiency

Elevated insulin levels, which cause the hypoglycemia and increase fatty acid mobilization from adipose tissue

A 29-year-old male decides to go on the Atkins diet. After approximately a month on the diet he complains of having what he describes as bad breath. What would be the biochemical findings in this patient?

Increased beta-oxidation due to increased activity of hormone sensitive lipase with subsequent increase in ketone bodies in plasma

Increased synthesis of fatty acids in adipose tissue due to excess free fatty acids released from adipose tissue

Decreased gluconeogenesis due to lack of activation of pyruvate carboxylase

Decreased levels of free fatty acids and undetectable ketone bodies in the plasma due to inactivation of LPL

Increased synthesis and recycling of fatty acids by the liver leading to increased adipose tissue storage of fats

Increased beta-oxidation due to increased activity of hormone sensitive lipase with subsequent increase in ketone bodies in plasma

What is the importance of citrate in fatty acid metabolism?

Activation of acetyl-CoA carboxylase

Activation of fatty acid synthetase

To act as a precursor for addition of one carbon units

Activation of acetyl-CoA carboxylase

To add the activated carbon dioxide in the formation of malonyl-CoA

Activation of carnitine acyl transferase

The reducing equivalents necessary for fatty acid synthesis are produced during the conversion of:

Glucose-6-phosphate to ribulose-5-phosphate

Glyceraldehyde-1, 3-bisphosphate to 3-phosphoglycerate

Glucose-6-phosphate to ribulose-5-phosphate

Glucose-6-phosphate to fructose-6-phosphate

A patient presents to your clinic complaining of weakness and pain in the muscle and a general lack of energy. A blood test shows that he has high levels of creatine kinase and myoglobin. Urine analysis reveals very low levels of acetoacetate. This patient most likely has which of the following?

Complete absence of medium chain acyl-CoA dehydrogenase

Deficiency in one of the enzymes in the ketone body synthetic pathway

A low fat, high carbohydrate diet

Decreased production of insulin

Dr Buxbaum The DRI of Vitamin A for an 18a old ♂ is: EAR 625 ug/d, RDA 900 ug/d and UL 2800 ug/d. A patient of that group taking on average 950 ag/d will suffer from symptoms of

Deﬁciency with a probability of about 2%

Poisoning with a probability of about 50%

Poisoning with a probability of about 2%

Deﬁciency with a probability of about 98%

Deﬁciency with a probability of about 2%

Deﬁciency with a probability of about 50%

A 4-month-old male was admitted to the hospital in a coma. Blood analysis taken on admission revealed a blood glucose of 15 mg/dL (normal 60-100 mg/dL). He had no acidosis or ketosis. A 24 hour fast produced a dramatic drop in blood glucose and a rise in serum triglycerides. Liver and muscle biopsy showed accumulation of fat. This infant most likely has

Hormone sensitive lipase deficiency

Type 1 glycogen storage disease

A 5mo old female was transferred to an emergency room in a rapidly deteriorating condition. She was born in Ville de Saguenay (Quebec), birth was uneventful. However, she failed to thrive. Lab: Glutamic:pyruvic transaminase (GPT), aspartate aminotransferase (AST), ammonia and creatinine levels in blood were elevated, attending physicians noticed a strong cabbage-like smell originating from her. The most likely diagnosis is

Glycine cleavage enzyme deﬁciency

When vitamin B12 is deficient, pernicious anemia results from the:

lack of N5, N10-methylenetetrahydrofolate

accumulation of S-adenosylmethionine

Block 6 The Buxbaum Files

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| Written by Chachelly

Chachelly

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Quizzes Created: 528 | Total Attempts: 566,272

Questions: 34 | Attempts: 665 | Updated: Mar 14, 2023

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Questions and Answers

1.

Differential scanning calorimetry (DSC) is a technique to follow phase transitions (like melting). Two chambers -one with buffer only, the other also containing the sample - are heated in parallel and the energy required for changing the temperature in both chambers is compared. As the sample approaches a phase transition temperature, it requires more energy to heat than the buffer (“excess heat" measured in J/(mol). Once the temperature passes the transition temperature, the excess heat drops to near 0 J/(mol) again. The experiment depicted below measures the “melting” (Lipid A -- > lipid B transition) in two samples of phosphatidylcholine Liposomes. The samples differ in the fatty acids that make up the phospholipid. To go from A to B, you have to replace
- A.
  
  Stearic with oleic acid
- B.
  
  Oleic with stearic acid
- C.
  
  Stearic with palmitic acid
- D.
  
  Palmitic with stearic acid
- E.
  
  Oleic with palmitoleic acid
Correct Answer
B. Oleic with stearic acid

Explanation
Replacement of an unsaturated (C18:1) with the corresponding saturated fatty acid (C18:0) increases the melting point significantly. Saturated fatty acids are straight, cis-unsaturated fatty acids have a 120* kink, this prevents tight packing in membranes increased fluidity. Mammals have membranes with a melting temperature of 10-12*C, well below body temp.

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2.

A.B. ill1-5 in above pedigree, was rather lethargic and unwilling to feed. On the 5th day of his life he was found unconscious in his bed, undergoing seizures. Blood tests revealed elevated concentrations of ammonia, glutamine, alanine and orotic acid. Since one of his uncles had died n early childhood blood ammonia levels were measured in all surviving family members (indicated from white (normal; over gray (slightly elevated) to black (very high) in the pedigree). Which of the following enzymes is most likely affected in this family?
- A.
  
  Ornithine transcarbamoylase
- B.
  
  Argininosuccinate synthetase
- C.
  
  Argininosuccinate lyase
- D.
  
  Argininase
- E.
  
  Carbamoylphosphate synthetase
Correct Answer
A. Ornithine transcarbamoylase

Explanation
Of all the enzymes of the urea cycle only ornithine transcarbamoylase is encoded on
the X-chromosome. This enzyme is the classical example for X-inactivation!

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3.

For your research project you want to isolate the enzyme argininosuccinate synthetase in the laboratory. Which starting material would you use?
- A.
  
  Brain peroxisome
- B.
  
  Brain nuclei
- C.
  
  Liver cytosol
- D.
  
  Liver mitochondria
- E.
  
  Kidney microsomes
Correct Answer
C. Liver cytosol

Explanation
P. The urea cycle occurs in the Liver
0. 2 of its reactions occur in the mitochondria: synthesis of
carbamoyiphosphate and its transfer onto ornithine.
 The remaining reactions occur in the cytosol

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4.

You are a young physician working with a disaster relief organization. You have been send to a developing country where a recent civil war has caused wide-spread malnutrition. A patient presents with weakness, muscle wasting, seizures, confusion, tachycardia and vomiting. There is edema in the lower body, which according to relatives has started in the feet and, moving upward, has now reached the thighs. This hypovitaminosis will affect the metabolism of which of the following amino acids:
- A.
  
  Asp and Glu
- B.
  
  Val, Ile and Leu
- C.
  
  Ser
- D.
  
  Pro and Arg
- E.
  
  Met
Correct Answer
B. Val, Ile and Leu

Explanation
The signs and symptoms correspond to wet Beri-beri
Beri-beri is thiamine deficiency. About 1.5 x 106 people are affected
worldwide, for example in the Philippines it is the 4th leading cause of
infant mortality.
Thiamin is required for oxidative decarboxylation reactions (pyruvate decarboxylase, ketoglutarate decarboxylase, branched chain ketoacid dehydrogenase). The accumulation of pyruvic aldehyde is considered to be the cause of symptoms.
In our context it is the metabolism of branched chain amino acids (Val, Leu, Ile) that is affected.

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5.

A.B. is a 40 a old female patient complaining of kidney stones. Microscopic examination of urine reveals hexagonal crystals. Elemental analysis shows that the crystals are made of a compound that contains sulphur. Family history reveals an autosomal recessive inheritance. The patient should NOT be treated by:
- A.
  
  Low protein diet
- B.
  
  Agents that increase urine pH (e.g. penicillamine)
- C.
  
  High fluid intake
- D.
  
  Surgical removal of stones
- E.
  
  Diuretics
Correct Answer
D. Surgical removal of stones

Explanation
the patient is suffering from cystnuria. one of the Leading causes for kidney stones
A low protein diet: reduces the amount of Cys that can be used to make cystine.
B agents that increase urine pH (e.g. penicillamine): increases the solubility of cystine.
C high fluid intake: increases urine volume and hence the amount of cystine that can be flushed from the body
D surgical removal of stones: unnecessarily invasive
E diuretics: also increases urine volume

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6.

Which amino acid plays an important role in pH-regulation in the kidney?
- A.
  
  Glutamine (Gln, Q)
- B.
  
  Asparagine (Asn, N)
- C.
  
  Lysine (Lys, K)
- D.
  
  Arginine (Arg, R)
- E.
  
  Tryptophan (Trp, W)
Correct Answer
A. Glutamine (Gln, Q)

Explanation
Glutamine breakdown is used to counter metabolic acidosis.

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7.

K.L. a 58a old female comes to your family practice because she is not feeling well. She has been suffering from dizziness, weakness and nausea with occasional vomiting for about 3 mo. She also complains about shortness of breath and tingling and numbness in her extremities. Physical exam reveals slightly icteric eyes, hepatosplenomegaly, glossitis, loss of balance, toss of vibratory and position sense in Legs. Lab results: Macrocytic, hypochromic anemia, leucopenia with hypersegmented neutrophils, thrombocytopenia, hyperbilirubinemia. There is no hydrochloric acid in stomach juice Your patient is suffering from
- A.
  
  Rickets
- B.
  
  Pellagra
- C.
  
  Ben-beri
- D.
  
  Pernicious anemia
- E.
  
  Scurvy
Correct Answer
D. Pernicious anemia

Explanation
The disease is most often due to autoantibodies against stomach parietal cells. This prevents the formation of HCl and intrinsic factor (atrophic gastritis). Treatment with parenteral Vit. B12.

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8.

A 2-week-old infant presents with vomiting, lethargy and convulsions without evidence of an infectious process. Laboratory examination reveals hyperammonemia with alkalosis. Glutamine, citrulline and arginine are found elevated in the blood. The enzyme that is most likely deficient in this patient is:
- A.
  
  Arginase
- B.
  
  Carbamoyl-phosphate synthetase I
- C.
  
  Arginosuccinate lyase
- D.
  
  Ornithine transcarbamoylase
- E.
  
  Arginosuccinate synthetase
Correct Answer
A. Arginase

Explanation
The presentation of vomiting, lethargy, and convulsions along with laboratory findings of hyperammonemia, alkalosis, and elevated levels of glutamine, citrulline, and arginine in the blood suggest a urea cycle disorder. The enzyme deficiency that best fits these findings is ornithine transcarbamoylase (OTC) deficiency. OTC is responsible for the conversion of ornithine and carbamoyl phosphate to citrulline in the urea cycle. Deficiency in OTC leads to the accumulation of carbamoyl phosphate, which is then converted to orotate, resulting in elevated levels of glutamine, citrulline, and arginine. Arginase deficiency would not result in hyperammonemia.

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9.

A nurse notices that the urine produced by a newborn infant has the odor of maple syrup. Which of the following pathways is most likely defective?
- A.
  
  Metabolism of branched-chain amino acids
- B.
  
  Metabolism of aromatic amino acids
- C.
  
  Metabolism of sulfur-containing amino acids
- D.
  
  Transformation of carbohydrates to amino acids
- E.
  
  One-carbon transfer reactions
Correct Answer
A. Metabolism of branched-chain amino acids

Explanation
The correct answer is "Metabolism of branched-chain amino acids." This is because the odor of maple syrup in urine is a characteristic symptom of maple syrup urine disease (MSUD), which is caused by a defect in the metabolism of branched-chain amino acids (leucine, isoleucine, and valine). In individuals with MSUD, these amino acids cannot be properly broken down and build up in the body, leading to various health issues. Therefore, the presence of the maple syrup odor suggests a defect in the metabolism of branched-chain amino acids.

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10.

A 1-year-old child with mental retardation has a deficiency of dihydrobiopterin reductase. This enzyme deficiency leads to an increased blood level of:
- A.
  
  Tyrosine
- B.
  
  Methionine
- C.
  
  Glucocerebroside
- D.
  
  Glycine
- E.
  
  Phenylalanine
Correct Answer
E. Phenylalanine

Explanation
Hawkinsinuria, increased Cl- in urine (swimming pool urine)

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11.

A patient reports to you that he has had aches and pains in his muscles for the past seven days. A blood test shows increased levels of creatine kinase MM, fatty acids and also myoglobin. A second blood sample, this time taken after an overnight fast, revealed low levels of blood glucose and elevated very low density lipoprotein (VLDL). This patient most likely has which of the following conditions?
- A.
  
  Essential amino acid deficiency
- B.
  
  Type 1 glycogen storage disease
- C.
  
  Acute alcohol toxicity
- D.
  
  Carnitine acyltranferase deficiency
- E.
  
  Elevated insulin levels, which cause the hypoglycemia and increase fatty acid mobilization from adipose tissue
Correct Answer
D. Carnitine acyltranferase deficiency

Explanation
Diseases of carnitine shuttle
Systemic primary carnitine deficiency: SLC22A5 gene on chromosome 5q31.1, renal re-uptake transporter OCTN2 (Na+-cotransport). Frequency Faroe Islands 1 in every 500, otherwise 1 in several 10000. OMIM #212140.
Hypoketotic hypoglycemia, Reye-syndrom like episodes, lethargy, somnolence, hepato- and cardiomegaly.
Treatment: oral supplementation of carnitine
Carnitine palmitoyltransferase I deficiency: hypoketotic hypoglycemia, Reye-syndrom like episodes,
hepatomegaly, muscle weakness. OMIM #255120.
Treatment: prevent hypoglycemia with short- and medium-chain fa in diet
Carnitine-acylcarnitine translocase deficiency: Presents within hours of birth with seizures, bradycardia, breathing problems, hypoketotic hypoglycemia, hyperammonemia, hepatomegaly, cardiomyopathy, muscle weakness, sudden infant death. OMIM #212138.
Treatment: low lipid intake, medium chain fa, carnitine, avoid strenuous exercise.
Carnitine palmitoyltransferase II deficiency: Three forms:
Adult: OMIM #255110. Muscle problems (myalgia, rhabdomyolysis, myoglobinuria) during attacks, otherwise normal. Attacks induced by exercise, fasting, high-fat diet, infection. Highly variable age of onset, | more strongly affected.
Infantile: OMIM #600649. Age of onset usually _ 1a, but sometimes later. Hypoketotic hypoglycemia, loss of consciousness and seizures, hepato- and cardiomegaly.
Neonate: OMIM #608836. Onset hours to days after birth, rapidly fatal from cardiac, respiratory or liver failure.
Neuronal migration defects, kidney dysorganization. carnitine formed in liver and kidney from Lys and Met
supplementation not required in healthy individual 12 C-atoms pass membrane by diffusion
distribution of acyl-CoA between cytosol (anabolic) and mito (catabolic)
rate-limiting step of FA breakdown!
( slide 20-22 F.A metab-BUX)

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12.

A 29-year-old male decides to go on the Atkins diet. After approximately a month on the diet he complains of having what he describes as bad breath. What would be the biochemical findings in this patient?
- A.
  
  Increased synthesis of fatty acids in adipose tissue due to excess free fatty acids released from adipose tissue
- B.
  
  Decreased gluconeogenesis due to lack of activation of pyruvate carboxylase
- C.
  
  Decreased levels of free fatty acids and undetectable ketone bodies in the plasma due to inactivation of LPL
- D.
  
  Increased synthesis and recycling of fatty acids by the liver leading to increased adipose tissue storage of fats
- E.
  
  Increased beta-oxidation due to increased activity of hormone sensitive lipase with subsequent increase in ketone bodies in plasma
Correct Answer
E. Increased beta-oxidation due to increased activity of hormone sensitive lipase with subsequent increase in ketone bodies in plasma

Explanation
The Atkins diet is a low carbohydrate, high fat diet that promotes the use of ketone bodies as an alternative fuel source. When the body is in a state of ketosis, it increases the breakdown of fatty acids through beta-oxidation to produce ketone bodies. This leads to an increased activity of hormone sensitive lipase, which breaks down triglycerides in adipose tissue to release fatty acids for beta-oxidation. The increased beta-oxidation results in an increase in ketone bodies in the plasma, which can cause a fruity or acetone-like breath odor. Therefore, the correct answer is increased beta-oxidation due to increased activity of hormone sensitive lipase with subsequent increase in ketone bodies in plasma.

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13.

What is the importance of citrate in fatty acid metabolism?
- A.
  
  Activation of fatty acid synthetase
- B.
  
  To act as a precursor for addition of one carbon units
- C.
  
  Activation of acetyl-CoA carboxylase
- D.
  
  To add the activated carbon dioxide in the formation of malonyl-CoA
- E.
  
  Activation of carnitine acyl transferase
Correct Answer
C. Activation of acetyl-CoA carboxylase

Explanation
FA synthesis and b-oxidation must not occur at the same time (futile cycle)
Compartmentalization: FA synthesis in cytosol, breakdown in mitocondria
Malonyl-CoA (substrate for FA synthesis) shuts down carnitine shuttle (rate-limiting step of FA breakdown)
FA synthesis regulated at acetyl-CoA carboxylase:
citrate signals good nutrition: allosteric
insulin=dephosphorylation=activation
glucagon + adrenalin=inc cAMP =phosphorylation=
inactivation
gene expression: insulin", glucagon#
( slide 57 F.A metab-BUX)

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14.

The reducing equivalents necessary for fatty acid synthesis are produced during the conversion of:
- A.
  
  Glyceraldehyde-1, 3-bisphosphate to 3-phosphoglycerate
- B.
  
  Glucose-6-phosphate to ribulose-5-phosphate
- C.
  
  Glucose-6-phosphate to fructose-6-phosphate
- D.
  
  Citrate to malate
- E.
  
  Pyruvate to lactate
Correct Answer
B. Glucose-6-phosphate to ribulose-5-phosphate

Explanation
During the conversion of glucose-6-phosphate to ribulose-5-phosphate, the enzyme glucose-6-phosphate dehydrogenase catalyzes the oxidation of glucose-6-phosphate to form 6-phosphogluconolactone. This reaction produces NADPH, which is a reducing equivalent necessary for fatty acid synthesis. Therefore, this conversion provides the reducing equivalents required for fatty acid synthesis.

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15.

When excess acetyl-CoA, produced by the liver, cannot be used by the TCA cycle, it accumulates in the body as:
- A.
  
  Glucose
- B.
  
  Triglycerides
- C.
  
  P-hydroxybutarate
- D.
  
  Acetyl-CoA
- E.
  
  Glycogen
Correct Answer
C. P-hydroxybutarate

Explanation
When excess acetyl-CoA cannot be used by the TCA cycle, it is converted into p-hydroxybutarate. This is a type of ketone body that accumulates in the body. Ketone bodies are produced as an alternative fuel source when glucose is not readily available, such as during fasting or in certain metabolic conditions. The accumulation of p-hydroxybutarate can occur in conditions like diabetic ketoacidosis or prolonged fasting, and it can lead to metabolic acidosis if not properly regulated.

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16.

A patient presents to your clinic complaining of weakness and pain in the muscle and a general lack of energy. A blood test shows that he has high levels of creatine kinase and myoglobin. Urine analysis reveals very low levels of acetoacetate. This patient most likely has which of the following?
- A.
  
  Complete absence of medium chain acyl-CoA dehydrogenase
- B.
  
  Deficiency in one of the enzymes in the ketone body synthetic pathway
- C.
  
  Carnitine deficiency
- D.
  
  A low fat, high carbohydrate diet
- E.
  
  Decreased production of insulin
Correct Answer
C. Carnitine deficiency

Explanation
Diseases of carnitine shuttle
Systemic primary carnitine deficiency: SLC22A5 gene on chromosome 5q31.1, renal re-uptake transporter OCTN2 (Na+-cotransport). Frequency Faroe Islands 1 in every 500, otherwise 1 in several 10000. OMIM #212140.
Hypoketotic hypoglycemia, Reye-syndrom like episodes, lethargy, somnolence, hepato- and cardiomegaly.
Treatment: oral supplementation of carnitine
Carnitine palmitoyltransferase I deficiency: hypoketotic hypoglycemia, Reye-syndrom like episodes,
hepatomegaly, muscle weakness. OMIM #255120.
Treatment: prevent hypoglycemia with short- and medium-chain fa in diet
Carnitine-acylcarnitine translocase deficiency: Presents within hours of birth with seizures, bradycardia, breathing problems, hypoketotic hypoglycemia, hyperammonemia, hepatomegaly, cardiomyopathy, muscle weakness, sudden infant death. OMIM #212138.
Treatment: low lipid intake, medium chain fa, carnitine, avoid strenuous exercise.
Carnitine palmitoyltransferase II deficiency: Three forms:
Adult: OMIM #255110. Muscle problems (myalgia, rhabdomyolysis, myoglobinuria) during attacks, otherwise normal. Attacks induced by exercise, fasting, high-fat diet, infection. Highly variable age of onset, | more strongly affected.
Infantile: OMIM #600649. Age of onset usually _ 1a, but sometimes later. Hypoketotic hypoglycemia, loss of consciousness and seizures, hepato- and cardiomegaly.
Neonate: OMIM #608836. Onset hours to days after birth, rapidly fatal from cardiac, respiratory or liver failure.
Neuronal migration defects, kidney dysorganization. carnitine formed in liver and kidney from Lys and Met
supplementation not required in healthy individual 12 C-atoms pass membrane by diffusion
distribution of acyl-CoA between cytosol (anabolic) and mito (catabolic)
rate-limiting step of FA breakdown! ( slide 20-22 F.A metab-BUX)

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17.

Dr Buxbaum The DRI of Vitamin A for an 18a old ♂ is: EAR 625 ug/d, RDA 900 ug/d and UL 2800 ug/d. A patient of that group taking on average 950 ag/d will suffer from symptoms of
- A.
  
  Poisoning with a probability of about 50%
- B.
  
  Poisoning with a probability of about 2%
- C.
  
  Deﬁciency with a probability of about 98%
- D.
  
  Deﬁciency with a probability of about 2%
- E.
  
  Deﬁciency with a probability of about 50%
Correct Answer
D. Deﬁciency with a probability of about 2%

Explanation
Estimated Average Requirement (EAR) intake meets requirements of half the healthy
individuals in a group (sex, age).
Recommended Dietary Allowance (RDA) best judgement of a group of experts on the daily
amounts that are sufficient and safe for a healthy individual. EAR
plus 2 standard deviations.
tolerable Upper intake Level (UL) highest level of daily intake that is likely to pose no risks of
adverse heath effects to almost all individuals of a group.
Dietary Reference Intake EAR, RDA and UL
Adequate Intake intake of a healthy reference population where data are insufficient to
determine EAR and hence RDA.
US Recommended Daily Allowance highest RDA (based on 1968 recommendations) in
any gender and age group above 4 years

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18.

A 4-month-old male was admitted to the hospital in a coma. Blood analysis taken on admission revealed a blood glucose of 15 mg/dL (normal 60-100 mg/dL). He had no acidosis or ketosis. A 24 hour fast produced a dramatic drop in blood glucose and a rise in serum triglycerides. Liver and muscle biopsy showed accumulation of fat. This infant most likely has
- A.
  
  Fructose intolerance
- B.
  
  Hormone sensitive lipase deficiency
- C.
  
  Type 1 glycogen storage disease
- D.
  
  Fat malabsorption
- E.
  
  Carnitine deficiency
Correct Answer
E. Carnitine deficiency

Explanation
Diseases of carnitine shuttle
Carnitine palmitoyltransferase II deficiency: Three forms:
I Adult: OMIM #255110. Muscle problems (myalgia, rhabdomyolysis, myoglobinuria) during attacks, otherwise normal. Attacks induced by exercise, fasting, high-fat diet, infection. Highly variable age of onset, | more strongly affected.
I Infantile: OMIM #600649. Age of onset usually 1a, but sometimes later. Hypoketotic hypoglycemia, loss of consciousness and seizures, hepato- and cardiomegaly.
I Neonate: Onset hours to days after birth, rapidly fatal from cardiac, respiratory or liver failure.
Neuronal migration defects, kidney dysorganization.
Treatment: low lipid intake, medium chain fa, carnitine, avoid strenuous exercise. Bezafibrate may induce enzyme expression.

I Systemic primary carnitine deficiency: SLC22A5 gene on chromosome 5q31.1, renal re-uptake transporter OCTN2 (Na+-cotransport). Frequency Faroe Islands 1 in every 500, otherwise 1 in several 10000. OMIM #212140. Hypoketotic hypoglycemia, Reye-syndrom like episodes, lethargy, somnolence, hepato- and cardiomegaly.
Treatment: oral supplementation of carnitine
I Carnitine palmitoyltransferase I deficiency: hypoketotic hypoglycemia, Reye-syndrom like episodes,
hepatomegaly, muscle weakness. OMIM #255120.
Treatment: prevent hypoglycemia with short- and medium-chain fa in diet
I Carnitine-acylcarnitine translocase deficiency: Presents within hours of birth with seizures, bradycardia, breathing problems, hypoketotic hypoglycemia, hyperammonemia, hepatomegaly, cardiomyopathy, muscle weakness, sudden infant death. OMIM #212138.
Treatment: low lipid intake, medium chain fa, carnitine, avoid strenuous exercise.
(slide 21 22 Buxb-FA met)

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19.

A.B. is on chitosan to help him reduce weight. He may have to supplement his diet with which of the following compounds?
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
Correct Answer
E. E

Explanation
Chitosan is a dietary supplement that is often used for weight loss. It is a fiber derived from the shells of crustaceans. Since chitosan is a fiber, it can bind to dietary fat in the digestive system, preventing its absorption and potentially aiding in weight loss. However, chitosan may also interfere with the absorption of certain vitamins and minerals. Therefore, it is recommended for individuals taking chitosan to supplement their diet with essential nutrients, such as vitamin E, which is why the correct answer is E.

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20.

A 5mo old female was transferred to an emergency room in a rapidly deteriorating condition. She was born in Ville de Saguenay (Quebec), birth was uneventful. However, she failed to thrive. Lab: Glutamic:pyruvic transaminase (GPT), aspartate aminotransferase (AST), ammonia and creatinine levels in blood were elevated, attending physicians noticed a strong cabbage-like smell originating from her. The most likely diagnosis is
- A.
  
  Hyperlysinemia
- B.
  
  Tyrosinemia I
- C.
  
  Cystinuria
- D.
  
  Methylmalonic aciduria
- E.
  
  Glycine cleavage enzyme deﬁciency
Correct Answer
B. Tyrosinemia I

Explanation
The elevated levels of GPT, AST, ammonia, and creatinine, along with the strong cabbage-like smell, suggest a metabolic disorder. One such disorder is Tyrosinemia I, which is characterized by the accumulation of tyrosine and its metabolites. This accumulation leads to liver and kidney damage, explaining the elevated liver enzymes and creatinine levels. The strong odor is caused by the accumulation of succinylacetone, a metabolite of tyrosine, which has a cabbage-like smell. Therefore, Tyrosinemia I is the most likely diagnosis for this 5-month-old female.

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21.

A 54-year-old male presents himself at an outpatient clinic complaining of weakness, lassitude and a weight loss of 20kg over the last 7mo. On Dr. E. Buxbaum examination pulse and respiratory rate, EKG and chest X-ray appeared normal. Blood pressure was 145/75 mm Hg, liver was ﬁrm and moderately enlarged (2 ﬁngers below costal margin). Upon questioning the patient remarked that his skin had become darker over the last years, a change he attributed to working outdoors. He denied exposure to toxic chemicals or metal fumes. Lab results: Fasting blood glucose 7.6mM (3.9–6.1mM), Urine glucose(random) + (0), total serum bilirubin 20 µM (2.6–26µM), Haemoglobin 16.5 g/dl (14.0–18.0g/dl) Haematocrit 52% (40–54%), Methemoglobin 0 (0), Serum iron 43 µM (7.2–28.6µM), total iron binding capacity (TIBC) 56µM (47–77µM), aspartate aminotransferase (AST) 50U/l(5–34U/l), alanine aminotransferase (ALT) 45U/l(5–50U/l), Serum ferritin 463µg/l (20–250 µg/l). On the basis of these results a liver biopsy was performed. Microscopic examination revealed fatty vacuolisation of the hepatocytes and moderate deposits of hemosiderin in their cytoplasm. Your diagnosis would be
- A.
  
  Hemochromatosis
- B.
  
  Wilson’s disease
- C.
  
  Menke’s kinky hair syndrome
- D.
  
  Keshan-disease
- E.
  
  Kashin-Beck disease
Correct Answer
A. Hemochromatosis

Explanation
The patient's symptoms, including weakness, lassitude, weight loss, and darkening of the skin, along with the findings of a firm and moderately enlarged liver, suggest a diagnosis of hemochromatosis. The lab results also support this diagnosis, with elevated fasting blood glucose, elevated serum iron, and elevated serum ferritin levels. The liver biopsy findings of fatty vacuolisation of hepatocytes and deposits of hemosiderin further confirm the diagnosis of hemochromatosis, a condition characterized by excessive iron absorption and deposition in various organs, including the liver. Wilson's disease, Menke's kinky hair syndrome, Keshan disease, and Kashin-Beck disease are unrelated conditions and do not fit the clinical presentation and lab findings described.

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22.

When vitamin B12 is deficient, pernicious anemia results from the:
- A.
  
  Lack of N5, N10-methylenetetrahydrofolate
- B.
  
  Accumulation of S-adenosylmethionine
- C.
  
  Lack of methionine
- D.
  
  Lack of 5-adenosylmethionine
- E.
  
  Accumulation of homocysteine
Correct Answer
A. Lack of N5, N10-methylenetetrahydrofolate

Explanation
When vitamin B12 is deficient, it leads to a lack of N5, N10-methylenetetrahydrofolate. This is because vitamin B12 is necessary for the conversion of homocysteine to methionine, and methionine is required for the synthesis of N5, N10-methylenetetrahydrofolate. Without enough N5, N10-methylenetetrahydrofolate, the body is unable to produce sufficient amounts of DNA and red blood cells, resulting in pernicious anemia.

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23.

A 47a old male comes to the emergency room with bleeding gums, hemarthrosis (blood collection) in the right knee, and hematemesis (vomiting blood). He is homeless, admits being drunk at least 5 times a week. His diet mainly consists of leftovers from fast food restaurants. Medical history: Food poisoning treated with ampicillin 2 weeks ago. Physical exam: emaciated, with poor hygiene, ecchymosis (large patches of bleeding into skin). Lab: Hb 9.7mg/d1. Normal platelet count, fibrinogen and thrombin time. PT and PTT prolonged. The patient needs supplementation with
- A.
  
  Vitamin A
- B.
  
  Vitamin K
- C.
  
  Vitamin C
- D.
  
  Copper
- E.
  
  Iron
Correct Answer
B. Vitamin K

Explanation
The patient's presentation of bleeding gums, hemarthrosis, hematemesis, and ecchymosis suggests a bleeding disorder. The prolonged PT and PTT indicate a deficiency in clotting factors. Vitamin K is essential for the synthesis of clotting factors II, VII, IX, and X. The patient's history of alcoholism and poor diet may contribute to a deficiency in vitamin K. Therefore, supplementation with vitamin K is necessary to correct the clotting abnormalities and prevent further bleeding episodes.

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24.

Joseph is a 55 year old man with pellagra, characterized by dementia, diarrhea and dermatitis. Which of the following vitamin deficiencies result in pellagra?
- A.
  
  Riboflavin
- B.
  
  Niacin
- C.
  
  Vitamin K
- D.
  
  Vitamin B12
- E.
  
  Vitamin E
Correct Answer
B. Niacin

Explanation
Pellagra is a vitamin deficiency disease most commonly caused by a chronic lack of niacin (vitamin B3) in the diet. It can be caused by decreased intake of niacin or tryptophan, and possibly by excessive intake of leucine. It may also result from alterations in protein metabolism in disorders such as carcinoid syndrome. A deficiency of the amino acid lysine can lead to a deficiency of niacin as well

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25.

Tim is s 52 year old man with a long-standing history of alcohol abuse, who comes to see his primary care physician because he has been losing balance lately. His wife related to the doctor that his memory is getting worse. Based on the patient's report what is the most likely Vitamin or mineral deficiency that would explain these symptoms?
- A.
  
  Vitamin D
- B.
  
  Calcium
- C.
  
  Vitamin A
- D.
  
  Vitamin C
- E.
  
  Thiamine
Correct Answer
E. Thiamine

Explanation
Thiamine deficiency, also known as vitamin B1 deficiency, is commonly associated with chronic alcohol abuse. Thiamine is essential for proper brain function, and its deficiency can lead to neurological symptoms such as memory loss and balance problems. Therefore, considering Tim's history of alcohol abuse and his symptoms of memory loss and balance issues, thiamine deficiency is the most likely explanation for his symptoms.

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26.

The Food and Drug Administration recommends that food be fortified with folic acid to reduce the incidence of birth defects such as spina bifida. A folic acid derivative is required for which of the following eukaryotic processes?
- A.
  
  Carboxylation of acetyl CoA to malonyl CoA
- B.
  
  Activation of methionine to form S-adenosylmethionine
- C.
  
  Absorption and uptake of vitamin B12
- D.
  
  Transamination reactions of amino acids.
- E.
  
  Thymidine synthesis
Correct Answer
E. Thymidine synthesis

Explanation
Folic acid is required for the synthesis of thymidine, which is an essential component of DNA. Thymidine synthesis is important for cell division and growth, including during the development of a fetus. By fortifying food with folic acid, the incidence of birth defects such as spina bifida can be reduced, as folic acid ensures proper DNA synthesis and cell division during fetal development.

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27.

Which of the following is true of the vitamin niacin? It:
- A.
  
  Functions primarily in the form of thiamin pyrophosphate.
- B.
  
  Is converted to the coenzymes FAD and FMN.
- C.
  
  Can be synthesized from tryptophan
- D.
  
  Is an essential component of coenzyme A
- E.
  
  Is the prosthetic group for a number of carboxylation reactions
Correct Answer
C. Can be synthesized from tryptophan

Explanation
Hartnup’s disease is a hereditary nutritional disorder resulting in niacin deficiency. It is due to a deficit in the intestines and kidneys, making it difficult for the body to break down and absorb dietary tryptophan. The resulting condition is similar to pellagra, including symptoms of red, scaly rash, and sensitivity to sunlight. Oral niacin is given as a treatment for this condition in doses ranging from 40–200 mg, with a good prognosis if identified and treated early. Niacin synthesis is also deficient in carcinoid syndrome, because of metabolic diversion of its precursor tryptophan to form serotonin.

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28.

Thiamin deficiency, which is common in alcoholics, slows the TCA cycle by decreasing the activity of a-ketoglutarate dehydrogenase. This deficiency also decreases the activity of another mitochondrial enzyme resulting in the build- up of pyruvate and a resulting lactic acidosis. The enzyme is:
- A.
  
  Pyruvate carboxylase
- B.
  
  Pyruvate kinase
- C.
  
  Citrate synthetase
- D.
  
  Pyruvate dehydrogenase
- E.
  
  Pyruvate decarboxylase
Correct Answer
D. Pyruvate dehydrogenase

Explanation
Thiamin deficiency in alcoholics slows down the TCA cycle by reducing the activity of a-ketoglutarate dehydrogenase. This deficiency also affects another mitochondrial enzyme, pyruvate dehydrogenase, leading to the accumulation of pyruvate and causing lactic acidosis. Therefore, the correct answer is Pyruvate dehydrogenase.

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29.

You are on a group hiking tour in South Tirol (Europe). You had a brilliant, if slightly strenuous day out and a nice dinner in the hotel, consisting of spinach-filled potato dumplings with tossed salad and fried eggs, accompanied by a local red wine. 2h later you are called to one of your companions, who is feeling sick. You find an elderly lady, pale, clammy, in obvious distress. She is complaining about abdominal pain, vomiting, belching, diarrhea and flatulence. After arranging transport to a local polyclinic you find that temperature, vital signs, EKG, serum analysis, chest and abdominal X-ray and ultrasound are normal. What is the most likely diagnosis?
- A.
  
  Acute myocardial infarct
- B.
  
  Stroke
- C.
  
  Fatigue
- D.
  
  Food poisoning
- E.
  
  Lactose incompatibility
Correct Answer
E. Lactose incompatibility

Explanation
according to buxbaum we should know that in this part of France they use Riccotta CHEESE to prepare their spinach. He also says 2hrs is too soon for food poisoning. (has he ever eaten at the shacks?)

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30.

A newborn presents with severe acidosis, vomiting, hypotonia and neurologic deficits. Serum analysis reveals elevated levels of lactate and alanine. These observations suggest a deficiency in which of the following enzymes ?
- A.
  
  Alanine aminotransferase
- B.
  
  Glutamate dehydrogenase
- C.
  
  Lactate dehydrogenase
- D.
  
  Pyruvate dehydrogenase
- E.
  
  Pyruvate carboxylase
Correct Answer
D. Pyruvate dehydrogenase

Explanation
The newborn presenting with severe acidosis, vomiting, hypotonia, and neurologic deficits, along with elevated levels of lactate and alanine in the serum, suggests a deficiency in the enzyme pyruvate dehydrogenase. Pyruvate dehydrogenase is responsible for converting pyruvate into acetyl-CoA, which is a crucial step in the production of energy in the form of ATP. A deficiency in this enzyme leads to the accumulation of pyruvate and lactate, causing the symptoms observed in the newborn.

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31.

High homocysteine levels are associated with an increased risk of atherosclerosis. A deficiency of which of the following enzymes would result in high blood levels of homocysteine (and also methionine)?
- A.
  
  Tyrosine hydroxylase
- B.
  
  Cystathionine synthase
- C.
  
  Threonine dehydratase
- D.
  
  Glutathione reductase
- E.
  
  L-amino acid oxidase
Correct Answer
B. Cystathionine synthase

Explanation
A deficiency of cystathionine synthase would result in high blood levels of homocysteine (and also methionine). Cystathionine synthase is an enzyme that plays a crucial role in the metabolism of homocysteine. It converts homocysteine to cystathionine, which is then further metabolized to produce cysteine. Without cystathionine synthase, homocysteine cannot be properly metabolized and accumulates in the blood, leading to high levels. This can increase the risk of atherosclerosis, as high homocysteine levels are associated with this condition.

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32.

Coconut protein is biologically inferior because it is lacking many essential amino acids. In your efforts to make transgenic coconuts with protein of high biological value, you should definitely ensure that your coconut protein has an adequate amount of:
- A.
  
  Glutamine
- B.
  
  Arginine
- C.
  
  Phenylalanine
- D.
  
  Tyrosine
- E.
  
  Serine
Correct Answer
C. Phenylalanine

Explanation
Phenylalanine is an essential amino acid that cannot be produced by the body and must be obtained from the diet. It plays a crucial role in protein synthesis and is necessary for the production of other important molecules such as neurotransmitters. Since coconut protein is biologically inferior due to its lack of essential amino acids, including phenylalanine in the transgenic coconut protein would help increase its biological value and make it more nutritionally complete.

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33.

The presence of phenylpyruvate and phenylketones in a child's blood are indications of the genetic disorder Phenylketonuria. How does this compound accumulate? This is a disorder of phenyalanine metabolism which results from:
- A.
  
  Too little product formation of a metabolic pathway
- B.
  
  Too much substrate accumulation for an enzymatic reaction
- C.
  
  An undersupply of tyrosine for protein translation
- D.
  
  An oversupply of homogentisic acid
- E.
  
  Modification of blood proteins by metabolic acids
Correct Answer
B. Too much substrate accumulation for an enzymatic reaction

Explanation
Phenylketonuria is a genetic disorder that affects the metabolism of phenylalanine. The correct answer states that the presence of phenylpyruvate and phenylketones in a child's blood indicates too much substrate accumulation for an enzymatic reaction. In individuals with phenylketonuria, there is a deficiency of the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine into tyrosine. As a result, phenylalanine accumulates in the body and is converted into phenylpyruvate and phenylketones. This accumulation of phenylalanine and its byproducts can lead to various health problems if not managed properly.

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34.

K.L. was born in Ville de Saguenay (Quebec), birth was uneventful. However, she failed to thrive. Suddenly at the age of 5 month her condition deteriorated rapidly and she was transferred to an emergency room. Organ function tests indicated failure of liver and kidney, attending physicians noticed a strong cabbage-like smell originating from her. The most likely diagnosis is
- A.
  
  Hyperlysinemia
- B.
  
  Cystinuria
- C.
  
  Methylmalonic aciduria
- D.
  
  Tyrosinemia I
- E.
  
  Glycine cleavage enzyme deficiency
Correct Answer
D. Tyrosinemia I

Explanation
The most likely diagnosis for K.L. based on the symptoms described is Tyrosinemia I. This is because the patient exhibited failure of liver and kidney, which are common symptoms of this condition. Additionally, the strong cabbage-like smell originating from her is a characteristic sign of tyrosinemia.

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Block 6 The Buxbaum Files

For your research project you want to isolate the enzyme argininosuccinate synthetase in the laboratory. Which starting material would you use?

Which amino acid plays an important role in pH-regulation in the kidney?

A nurse notices that the urine produced by a newborn infant has the odor of maple syrup. Which of the following pathways is most likely defective?

A 1-year-old child with mental retardation has a deficiency of dihydrobiopterin reductase. This enzyme deficiency leads to an increased blood level of:

A 29-year-old male decides to go on the Atkins diet. After approximately a month on the diet he complains of having what he describes as bad breath. What would be the biochemical findings in this patient?

What is the importance of citrate in fatty acid metabolism?

The reducing equivalents necessary for fatty acid synthesis are produced during the conversion of:

When excess acetyl-CoA, produced by the liver, cannot be used by the TCA cycle, it accumulates in the body as:

A patient presents to your clinic complaining of weakness and pain in the muscle and a general lack of energy. A blood test shows that he has high levels of creatine kinase and myoglobin. Urine analysis reveals very low levels of acetoacetate. This patient most likely has which of the following?

Dr Buxbaum The DRI of Vitamin A for an 18a old ♂ is: EAR 625 ug/d, RDA 900 ug/d and UL 2800 ug/d. A patient of that group taking on average 950 ag/d will suffer from symptoms of

A.B. is on chitosan to help him reduce weight. He may have to supplement his diet with which of the following compounds?

When vitamin B12 is deficient, pernicious anemia results from the:

Joseph is a 55 year old man with pellagra, characterized by dementia, diarrhea and dermatitis. Which of the following vitamin deficiencies result in pellagra?

The Food and Drug Administration recommends that food be fortified with folic acid to reduce the incidence of birth defects such as spina bifida. A folic acid derivative is required for which of the following eukaryotic processes?

Which of the following is true of the vitamin niacin? It:

Thiamin deficiency, which is common in alcoholics, slows the TCA cycle by decreasing the activity of a-ketoglutarate dehydrogenase. This deficiency also decreases the activity of another mitochondrial enzyme resulting in the build- up of pyruvate and a resulting lactic acidosis. The enzyme is:

A newborn presents with severe acidosis, vomiting, hypotonia and neurologic deficits. Serum analysis reveals elevated levels of lactate and alanine. These observations suggest a deficiency in which of the following enzymes ?

High homocysteine levels are associated with an increased risk of atherosclerosis. A deficiency of which of the following enzymes would result in high blood levels of homocysteine (and also methionine)?

Coconut protein is biologically inferior because it is lacking many essential amino acids. In your efforts to make transgenic coconuts with protein of high biological value, you should definitely ensure that your coconut protein has an adequate amount of:

The presence of phenylpyruvate and phenylketones in a child's blood are indications of the genetic disorder Phenylketonuria. How does this compound accumulate? This is a disorder of phenyalanine metabolism which results from: