neurologic disorders
Huntington Disease
Pathophysiology of Huntington Disease
In Huntington disease, the caudate nucleus atrophies, the inhibitory medium spiny neurons in the corpus striatum degenerate, and levels of the neurotransmitters gamma-aminobutyric acid (GABA) and substance P decrease. Huntington disease results from a mutation in thehuntingtin(HTT) gene (on chromosome 4), causing abnormal repetition of the DNA sequence CAG, which codes for the amino acid glutamine. The resulting gene product, a large protein called huntingtin, has an expanded stretch of polyglutamine residues, which accumulate within neurons and lead to disease via unknown mechanisms. The more CAG repeats, the earlier the onset of disease and the more severe its expression (phenotype). The number of CAG repeats can increase with successive generations when the father transmits the mutation and, over time, can lead to increasingly severe phenotypes within a family (called anticipation). 