Evidence for a late onset bipolar-I disorder sub-group from 50 years

Background: Age of onset has been used to identify aetiological sub-groups in complex inherited disorders such as Alzheimer’s disease and osteoarthritis. We examined the relationship between age of onset and family history in bipolar-I disorder in an attempt to identify subgroups. Methods: All patients discharged from a district in-patient service diagnosed with bipolar disorder in a 7-year period were ascertained from a case register (n=277). Diagnosis by DSM-IIIR criteria was confirmed; family history and age of first admission were recorded from case notes. Results: Age of first admission in those with a negative family psychiatric history was significantly older (P=0.029) with a skewed age distribution. This non-familial group contained significantly more subjects with first admission from the age of 50 years (P=0.007). Conclusions: Patients with bipolar-I disorder whose age of first admission is 50 years or above may belong to a different aetiological sub-group.