Prevalence of Huntington's disease gene CAG trinucleotide repeat alleles in patients with bipolar disorder

ObjectivesHuntington's disease is a neurodegenerative disorder characterized by motor, cognitive, and psychiatric symptoms that are caused by huntingtin gene (HTT) CAG trinucleotide repeat alleles of 36 or more units. A greater than expected prevalence of incompletely penetrant HTTCAG repeat alleles observed among individuals diagnosed with major depressive disorder raises the possibility that another mood disorder, bipolar disorder, could likewise be associated with Huntington's disease. MethodsWe assessed the distribution of HTTCAG repeat alleles in a cohort of individuals with bipolar disorder. HTTCAG allele sizes from 2,229 Caucasian individuals diagnosed with DSM-IV bipolar disorder were compared to allele sizes in 1,828 control individuals from multiple cohorts. ResultsWe found that HTTCAG repeat alleles > 35units were observed in only one of 4,458 chromosomes from individuals with bipolar disorder, compared to three of 3,656 chromosomes from control subjects. ConclusionsThese findings do not support an association between bipolar disorder and Huntington's disease.