Which gene is affected by a trinucleotide repeat leading to Huntington's disease?

The gene affected by a trinucleotide repeat in individuals with Huntington's disease is the Huntingtin gene. This gene is located on chromosome 4 and contains a repeating segment of nucleotides, specifically CAG (cytosine, adenine, guanine). In healthy individuals, this repeat occurs a relatively stable number of times, but in those with Huntington's disease, the repeat is expanded, resulting in an abnormally high number of repeats.

This expansion leads to the production of a mutant form of the huntingtin protein, which accumulates in neuronal cells and ultimately causes the neurodegenerative symptoms associated with the disease, such as movement disorders, cognitive decline, and psychiatric issues. The process is a classic example of how genetic mutations can lead to specific disease phenotypes, particularly when they involve repetitive sequences that can expand in successive generations.

The other genes listed—BRCA1, TP53, and APOE—are associated with different health conditions. BRCA1 relates to breast and ovarian cancer susceptibility, TP53 is known for its role in cancer suppression, and APOE is involved in cholesterol metabolism and is linked to Alzheimer's disease. Therefore, these genes are not involved in the pathology of Huntington's disease, making the Huntingtin gene the correct