Possible Association between SNAP-25 Single Nucleotide Polymorphisms and Alterations of Categorical Fluency and Functional MRI Parameters in Alzheimer’s Disease

Synaptosomal-associated protein of 25 kDa (SNAP-25) is an age-regulated vesicular SNARE protein involved in the exocytosis of neurotransmitters from synapses, a process that is altered in Alzheimer's disease (AD). Changes in SNAP-25 levels are suggested to contribute to age-related decline of cognitive function, and single nucleotide polymorphisms (SNPs) in the SNAP-25 gene are present in neuropsychiatric conditions and play a role in determining IQ phenotypes. To verify a possible role of SNAP-25 in AD, we analyzed five gene polymorphisms in patients with AD (n = 607), replicating the study in subjects with amnestic mild cognitive impairment (aMCI) (n = 148) and in two groups of age-matched healthy controls (HC1: n = 615 and HC2: n = 310). Results showed that the intronic rs363050 (A) and rs363043 (T) alleles, as well as the rs363050/rs363043 A-T haplotype are significantly more frequent in AD and aMCI and are associated with pathological scores of categorical fluency in AD. Notably, functional MRI analyses indicated that SNAP-25 genotypes correlate with a significantly decreased brain activity in the cingulate cortex and in the frontal (middle and superior gyri) and the temporo-parietal (angular gyrus) area. SNAP-25 polymorphisms may be associated with AD and correlate with alterations in categorical fluency and a reduced localized brain activity. SNAP-25 polymorphisms could be used as surrogate markers for the diagnosis of AD and of cognitive deficit; these SNPs might also have a possible predictive role in the natural history of AD.