Question

A 6-year-old boy cannot play soccer or participate in gym class. He staggers when he walks and falls frequently. In addition to this ataxic gait, the pediatrician notes the abnormally high arch of his feet and discovers a dysrhythmia on further work-up. The family reports that the boy's uncle also has this condition, but his symptoms did not appear until he was 12 years of age.

What is the molecular mechanism of this disease?
A. Unstable repeats affect protein folding
B. Unstable repeats affect protein splicing
C. Unstable repeats cause an amino acid substitution
D. Unstable repeats impede gene transcription
E. Unstable repeats result in a truncated protein

Answer 1

The symptoms described, including the ataxic gait and high arches of the feet, along with family history, suggest a spinocerebellar ataxia. The molecular mechanism is likely the effect of unstable repeats on protein folding due to extended CAG-repeats causing misfolded proteins, thereby leading to neurotoxicity and neuronal death.

The correct option is A. Unstable repeats affect protein folding

Step-by-step explanation:

The clinical features described, such as the ataxic gait, high arches of the feet, and the presence of dysrhythmia, in conjunction with the family history of a similar condition, suggest a neurological genetic disorder. Given the information about the uncle's condition manifesting later in life, which is characteristic of certain inherited neurodegenerative diseases, and the likely underlying molecular mechanism, the disease can be associated with a class of disorders known as spinocerebellar ataxias (SCAs). These disorders are typically inherited in an autosomal dominant pattern. Specifically, this condition might be caused by unstable repeats affecting protein folding, as seen in SCAs that involve the expansion of CAG-repeats in certain genes. These extended CAG repeats result in long polyglutamine sequences within the translated proteins, leading to protein misfolding and aggregation, which is neurotoxic and can cause neuronal death. Therefore, the molecular mechanism of this disease is likely Option A: Unstable repeats affect protein folding.

The correct option is A. Unstable repeats affect protein folding