Allelic distribution of CTG18.1 in Caucasian populations: association studies in bipolar disorder, schizophrenia, and ataxia

CTG18.1 is a highly polymorphic and unstable CTG repeat within an intron of the SEF2-1 gene. We tested the CTG18.1 repeat length in affective disorder , schizophrenia, and nonspecific ataxia; these diseases all have shown clin ical evidence for anticipation. There was no difference in the allele frequ encies comparing the controls and disease groups. The most common allele co ntains 11 CAGs (35%) followed by alleles with 14-17 CAGs (35%). There was n o difference in the distribution of the alleles in the cases vs controls fo r ataxia (P = 0.11), affective disorders (P = 0.21), or schizophrenia (P = 0.26). The frequency of unstable CTG18.1 alleles was approximately 3% in a population of N. European descent and is not related to the phenotypes test ed.