Prominent psychiatric features and early onset in an inherited prion disease with a new insertional mutation in the prion protein gene.

In five generations of the French M-E kindred, 11 members are now known to be or have been affected by a form of spongiform encephalopathy previously recorded as Gerstmann-Sträussler-Scheinker disease. Mean age at onset was 28 years (range 21-34 years). In six instances, these patients were hospitalized in psychiatric institutions with various diagnoses, the most frequent being mania or mania-like symptoms.