An African American family with early-onset Alzheimer disease and an APP (T714I) mutation.

The occurrence of an APP T174I mutation is described in a large American family of African descent with Alzheimer disease. The clinical characteristics were an unusually early onset of disease (early 30s), similar to a previously reported age at onset of this mutation in an Austrian family. Distinct from that family, seizures and myoclonus were prominent features of the disease in this kindred.