Question

A 45-year-old man comes to a physician accompanied by his wife. They report that the patient has been struggling with depression for over a year now. He had no past history of psychiatric illness prior to the onset of his current depressive symptoms. In addition, he has become more irritable lately. They are also concerned because recently he has been restless and constantly moving his arms in a rapid, nonrythmic manner that he cannot suppress. The patient's wife notes that her father-in-law developed similar symptoms in his 60s and later developed dementia.

What is the biologic basis of this patient 's likely condition?
A. α-Synuclein concretions
B. Aggregated tau proteins
C. CAG repeats
D. Organ-specific amyloidosis
E. SOD1 defect

Answer 1

The biologic basis for the 45-year-old man's symptoms, which are indicative of Huntington's disease, is CAG repeats in the HTT gene leading to a mutated huntingtin protein.

Step-by-step explanation:

The symptoms described for the 45-year-old man, including depression, irritability, and restlessness with rapid, nonrhythmic movements of his arms that he cannot suppress, suggest a neurodegenerative disorder. The fact that similar symptoms were observed in his father, who later developed dementia, and considering the genetic component, indicates that the man is likely suffering from Huntington's disease. The biologic basis for this patient's condition is CAG repeats, which refers to a type of genetic mutation where a sequence of three DNA bases (cytosine, adenine, and guanine) is repeated excessively in a gene. This type of repeat mutation occurs in the HTT gene for Huntington's disease, leading to the production of an abnormally long version of the huntingtin protein, which ultimately results in the symptoms of the disease.