Amyloid Precursor Protein Variant, E665D, Associated With Unique Clinical and Biomarker Phenotype.

We describe a clinical, imaging and biomarker phenotype associated with an amyloid precursor gene (APP) E665D variant in a 45-year-old man with progressive cognitive and behavioral dysfunction. Brain MRI showed bilateral, confluent T2 hyperintensities predominantly in the anterior white matter. Amyloid imaging and CSF testing were consistent with amyloid deposition. 7 Tesla MRI revealed cerebral microhemorrhages suggestive of cerebral amyloid angiopathy (CAA). Contrary to previous reports, this case raises the possibility that the APP E665D genetic change may be pathogenic, particularly given the abnormal Alzheimer's disease biomarkers observed in the cerebrospinal fluid, positive amyloid imaging and imaging evidence for CAA in a relatively young patient with progressive cognitive decline.