Missense mutations in the genes encoding amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) have been found to cause some forms of autosomal dominant early onset Alzheimer disease (AD). Autosomal dominant point mutations in the APP gene are associated with β-amyloid peptide related cerebral amyloid angiopathy (CAA) and AD.1 Duplications of the APP locus on chromosome 21 have recently been reported to be associated with a phenotype similar to that caused by point mutations in the APP gene, including progressive AD and strokes and intracerebral haemorrhage (ICH) of variable frequency.2^–4 The neuropathological findings have been consistent with a diagnosis of definite AD according to the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD). The most prominent feature in all cases has been severe CAA in the leptomeningeal vessels together with superficial and deep intraparenchymatous small arteries, capillaries and venules.

We have previously described detailed clinical features of a four generation Finnish family, including 14 …