CAG repeat sequences in bipolar affective disorder: no evidence for association in a French population

Anticipation has been described in bipolar affective disorder (BPAD). However, there are conflicting results from association studies screening for a link between BPAD and CAG/CTG repeat expansions, the molecular basis of anticipation in several hereditary neurodegenerative disorders. Here, the repeat expansion detection (RED) method was used to screen for CAG repeat expansion in 119 French BPAD patients. Western blotting was also used to search for polyglutamine stretches, encoded by CAG expansion, among proteins, extracted from lymphoblastoid cell lines, from six selected familial cases. Maximum CAG/CTG repeat length did not differ significantly (P = 0.38) between the 119 BPAD patients and the 88 controls included in the study. Several categories of subgroups were used, none of which showed significant association with a long repeat. Nor was a specific protein with an unusually long polyglutamine stretch (lower detection limit, approximately 33 polyglutamines) detected in cell lysates from the familial cases studied. In conclusion, an association between a long CAG/CTG repeat and BPAD in the French population sample studied was not found. Nonetheless, a short repeat (<40 repeats) might still be implicated, and this possibility warrants further study.