Objective

To report the clinical, electroencephalographic, and neuroradiologic findings in a kindred with a novel insertion in the prion protein gene (PRNP).

Design

Clinical description of a kindred.

Setting

Mayo Clinic Alzheimer’s Disease Research Center (Rochester).

Subjects

Two pathologically-confirmed cases and their relatives.

Main outcome measures

Clinical features, electroencephalographic patterns, magnetic resonance imaging abnormalities, genetic analyses and neuropathological features.

Results

The proband presented with clinical and neuroimaging features of atypical frontotemporal dementia (FTD) and ataxia. Generalized tonic-clonic seizures developed later in her course, and electroencephalography revealed spike and wave discharges but no periodic sharp wave complexes. Her affected sister and father also exhibited FTD-like features, and both experienced generalized tonic-clonic seizures and gait ataxia late in their course. Genetic analyses in the proband identified a novel defect in PRNP with one mutated allele carrying a 288 base pair insertion (BPI) consisting of 12 octapeptide repeats. Neuropathologic examination of the sister and proband revealed PrP-positive plaques and widespread tau-positive tangles.

Conclusion

This kindred has a unique combination of clinical and neuropathologic features associated with the largest BPI identified to date in PRNP, and underscores the need to consider familial prion disease in the differential diagnosis of a familial FTD-like syndrome.