Huntington disease is caused by a mutation on which chromosome?

Huntington disease is caused by a mutation on which chromosome?

• A. Chromosome 4
• B. Chromosome 21
• C. Chromosome X
• D. Chromosome 7

Answer: (A)

Huntington disease is due to an unstable expansion of a CAG repeat in the HTT gene located on chromosome 4. This expanded repeat produces a toxic huntingtin protein that progressively damages neurons in the striatum (especially the caudate and putamen) and later cortical areas, leading to chorea, cognitive decline, and psychiatric symptoms. The inheritance is autosomal dominant, with anticipation—earlier onset in subsequent generations due to increasing repeat length. That’s why chromosome 4 is the correct location. The other chromosome options are associated with different conditions (for example, chromosome 21 with Down syndrome; the X chromosome with X-linked disorders), not Huntington disease.

Huntington disease is due to an unstable expansion of a CAG repeat in the HTT gene located on chromosome 4. This expanded repeat produces a toxic huntingtin protein that progressively damages neurons in the striatum (especially the caudate and putamen) and later cortical areas, leading to chorea, cognitive decline, and psychiatric symptoms. The inheritance is autosomal dominant, with anticipation—earlier onset in subsequent generations due to increasing repeat length.

That’s why chromosome 4 is the correct location. The other chromosome options are associated with different conditions (for example, chromosome 21 with Down syndrome; the X chromosome with X-linked disorders), not Huntington disease.