Question

A 42-year-old man presents to the clinic with complaints of uncontrollable movements. During the interview, he seems depressed and states that he has "known this was coming for a long time now." He states his father suffered from a movement disorder and eventually cognitive decline. You note that he exhibits some mild involuntary writhing movements in his limbs.

Which of the following is the likely cause of this disease?
A. Expansion of CAG trinucleotide repeats on chromosome 4
B. Expansion of CCG trinucleotide repeats on chromosome 11
C. Expansion of CGG trinucleotide repeats on chromosome X
D. Expansion of CTG trinucleotide repeats on chromosome 19
E. Expansion of GAA trinucleotide repeats on chromosome 9

Answer 1

The man's symptoms and family history suggest Huntington's Disease, caused by the expansion of CAG trinucleotide repeats on chromosome 4.

Step-by-step explanation:

The likely cause of the disease in a 42-year-old man with a family history of a movement disorder and uncontrollable movements is Huntington's Disease (HD). HD is characterized by involuntary spastic movements and difficulty in controlling voluntary movement, which often presents along with cognitive decline. The cause of HD is a mutation resulting in an expansion of CAG trinucleotide repeats on chromosome 4. This genetic anomaly leads to the production of an abnormally long version of the huntingtin protein, which eventually causes neuronal cell death and the symptoms observed in the patient.