Ectopic White Matter Neurons, a Developmental Abnormality That May Be Caused by the PSEN1 S169L Mutation in a Case of Familial AD with Myoclonus and Seizures

We report clinical, neuropathologic and molecular genetic data from an individual affected by a familial Alzheimer disease (AD) variant. The proband had an onset of dementia at age 29 followed by generalized seizures a year later. He died at age 40. Neuropathologically, he had severe brain atrophy and characteristic histopathologic lesions of AD. Three additional neuropathologic features need to be emphasized: 1) severe deposition of Aβ in the form of diffuse deposits in the cerebral and cerebellar cortices, 2) numerous Aβ deposits in the subcortical white matter and in the centrum semiovale, and 3) numerous ectopic neurons, often containing tau-immunopositive neurofibrillary tangles, in the white matter of the frontal and temporal lobes. A molecular genetic analysis of DNA extracted from brain tissue of the proband revealed a S169L mutation in the Presenilin 1 (PSEN1) gene. The importance of this case lies in the presence of ectopic neurons in the white matter, early-onset seizures, and a PSEN1 mutation. We hypothesize that the PSEN1 mutation may have a causal relationship with an abnormality in neuronal development.