Accumulation of amyloid in plaques is a characteristic feature of Alzheimer's disease (AD) and may be an important factor in the pathogenesis this disorder. These amyloid deposits contain beta-amyloid encoded by exons 16 and 17 of the amyloid precursor protein (APP) gene. For some AD patients, disturbance in the structure or function of the APP gene may contribute to amyloid accumulation. This primary role for the APP gene is supported by the recent finding that 3 mutations altered the same APP codon in 7 unrelated familial AD kindreds. These-mutations are rare and it is quite likely that there are other AD-specific APP mutations. I will use denaturing gradient gel electrophoresis and direct DNA sequencing to detect additional APP mutations samples from at least 300 AD patients. I have used these extremely sensitive methods to detect a novel mutation in the prion gene in Creutzfeldt-Jakob disease. Defining the precise nature and location of APP mutations will tremendously advance our understanding of the mechanisms by which APP contributes to amyloid formation in AD. For some Alzhiemer's patients, amyloid accumulation could be related not to a structural change in the APP gene but to disturbance in this gene's transcriptional regulation or splicing pattern. There is evidence, for example, that the pattern of APP mRNA splicing is altered in brain regions which accumulate amyloid. I have recently discovered marked, tissue-specific differences in the abundance of APP mRNA transcripts arising from normal and mutant APP alleles in samples from AD patients. This may be an unusual finding because both alleles of most autosomal genes are presumed to be similarly regulated in a given tissue. These findings suggest that the APP gene may be under complex and relatively unique regulation. I will extend these investigations by determining whether marked differences in the abundance of mRNA derived from normal and mutant APP alleles are due to tissue-specific differences in the rates of transcription or variable mRNA stability. Greater understanding of the tissue-specific regulation of APP mRNA transcription, splicing, termination, and stability is extremely important because it is likely that, for some AD patients, disturbance of this regulation contributes to amyloid formation.
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