Which Trinucleotide Repeat Is Associated with Hd

There are several known categories of trinucleotide repeat disorder. Category I includes Huntington’s disease (HD) and the spinocerebellar ataxias. These are caused by a CAG repeat expansion in protein-coding portions, or exons, of specific genes.

What is the trinucleotide repeat sequence in Huntington's?

The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat . This segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row. Normally, the CAG segment is repeated 10 to 35 times within the gene.

How do trinucleotide repeats affect the phenotype of Huntington's disease?

When the trinucleotide repeat lies within the gene-coding region as in Huntington disease, its expansion results in an abnormal protein with a gain of function due to the enlargement of the polyglutamine tract.