A 4-year-old girl developed clumsiness and difficulty ambulating over 6 months. On physical examination, she showed
difficulty with balance while walking, dysarthria, poor hand coordination, absent deep tendon reflexes, and a bilateral
Babinski sign. Light touch and vibratory sensation were greatly diminished. There was no muscular weakness. Over the
next 5 years, she developed congestive heart failure from hypertrophic cardiomyopathy. She also had hyperglycemia. At
autopsy, there was increased perinuclear iron deposition within cardiac myocytes. Which of the following genetic
abnormalities with trinucleotide repeat expansions was most likely present in this patient?
A. CAG repeats in the huntingtin gene B. CAG repeats in the spinocerebellar ataxia 7 gene C. CGG repeats in the FMR1 gene D. CTG repeats in the dystrophila myotonia-protein kinase gene E. GAA repeats in the frataxin gene
Gaa repeats in the frataxin gene-(e) she had friedreich ataxia, an autosomal recessive progressive illness that most often has an onset in the first
decade of life. the frataxin gene encodes for a protein involved in iron regulation in cells. the other options listed have no
cardiac involvement. mutations of the huntingtin gene are seen with huntington disease marked by choreoathetosis
beginning in young to middle-aged adults. there are several forms of spinocerebellar ataxia. increased tandem repeats in
the fmr1 gene account for cases of fragile x syndrome characterized by mental retardation. the dystrophila myotonia
protein kinase gene is abnormal in cases of myotonic dystrophy with muscular weakness and dementia.
bp8 410, 896pbd8 1323