Review Question - QID 106528

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Friedreich Ataxia Introduction Autosomal recessive QID: 106528 (M1.NE.15.72)

QID 106528 (Type "106528" in App Search)

An 8-year-old boy is brought to the pediatrician because his mother is concerned about recent behavioral changes. His mother states that she has started to notice that he is slurring his speech and seems to be falling more than normal. On exam, the pediatrician observes the boy has pes cavus, hammer toes, and kyposcoliosis. Based on these findings, the pediatrician is concerned the child has a trinucleotide repeat disease. Which of the following trinucleotide repeats is this child most likely to possess?

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CGG

12/160

GAA

59%

94/160

CAG

17%

27/160

CTG

12/160

GCC

8/160

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Friedreich's ataxia (FA) is caused by the GAA trinucleotide repeat on chromosome 9.

Friedreich's ataxia is an autosomal-recessive trinucleotide repeat (GAA) disorder in the gene that encodes frataxin. The GAA repeat causes reduced frataxin levels, which results in mitochondrial iron overload and dysfunction. Common signs and symptoms of FA include staggering gait, frequent falling, nystagmus, dysarthria, pes cavus, kyphoscoliosis, and hammer toes. The characteristic staggering and falls are caused by degeneration of the spinocerebellar tracts and dorsal columns. It is closely associated with hypertrophic cardiomyopathy, which is the most common cause of death in patients with FA.

Koeppen et al. examined the neurologic basis and involvement of the dentate nucleus in FA. They examined 29 autopsy cases of FA and 2 carriers by measuring the thickness of the gray matter ribbon in the dentate nucleus and found that there was thinning of the dentate nucleus. Furthermore they found that immunohistochemical staining confirmed severe loss of GABA-A and glycine receptors in the dentate nucleus.

Weidemann et al. review the cardiovascular manifestations and defects relating to FA. They review the clinical and diagnostic features of cardiomyopathy and discusses potential treatments for Friedreich's ataxia. They state that there is currently no specific treatment available for such cardiomyopathy caused by FA. However, general cardiac therapeutic treatment options should be followed even for patients with freidreich's ataxia.

Incorrect Answers:
Answer 1: The CGG trinucleotide repeat is observed in Fragile X syndrome.
Answer 3: The CAG trinucleotide repeat is observed in Huntington's disease
Answer 4: The CTG trinucleotide repeat is observed in Myotonic dystrophy.
Answer 5: The GCC trinucleotide repeat is not a characteristic repeat seen in the trinucleotide repeat expansion disease.