Genetic factors are of major aetiological importance in bipolar disorder and schizophrenia. The exact mode of inheritance is unknown, but recent arguments in favor of genetic anticipation in those two disorders suggest that dynamic mutations could be involved. Using a new antibody, we thus explored the implication of large expanded polyglutamine tracts in a sample of very early onset schizophrenic and bipolar patients. No evidence for a specific protein with polyglutamine expansion was found in either group.