A cardiac dysrhythmia

A 6-year-old boy is diagnosed with a worsening ataxic gait and a cardiac dysrhythmia. His 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
© Unstable repeats cause an amino acid substitution
(D) Unstable repeats impede protein translation
(E) Unstable repeats result in a truncated protein