CAG Counts Unrelated to Psychiatric Symptoms in HD.

CAG counts are not related to the probability of developing a psychiatric disorder nor the severity of psychiatric symptoms in HD gene carriers.
Symptoms in Huntington's Disease vary from individual to individual and throughout the course of the disease. Not everyone develops all of the possible symptoms and a particular symptom which does develop may not be present throughout the entire course of the disease.

This study supports other research which has failed to find a connection between the CAG count and the likelihood of developing psychiatric symptoms or the severity of such symptoms.

Marsha L. Miller, Ph.D.
Effect of CAG repeat length on psychiatric disorders in Huntington’snext term disease
Evangelos Vassos, Marios Panas, Athina Kladi, and Dimitrios Vassilopoulos
There is strong evidence that the length of CAG repeats, in patients with Huntington's disease (HD), govern the age of onset and the rate of clinical progression of neurological symptoms. However, psychiatric manifestations of the disease have not been examined as comprehensively. Seventy two Greek patients with Huntington's disease had DNA testing and were clinically assessed by means of a semi-structured interview (SCID) and four self-rated questionnaires. Genotype-phenotype correlations were examined. The CAG repeat length had a significant negative association with the age of onset of psychiatric disorders, the total level of functioning and the MMSE. However, the probability of developing a psychiatric disorder and the severity of psychiatric symptoms were not determined by the trinucleotide expansion, after controlling for the duration of illness, sex, and age of the subjects. The factors that determine the development of psychiatric symptoms in HD patients seem not to be limited to a dose related toxicity of the expanded Huntington. It is hypothesized that alternative genetic or environmental factors underlie the pathogenesis of the psychiatric phenotype.
Journal of Psychiatric Research 2007 Jul 2; [Epub ahead of print]