The serotonin transporter promoter polymorphic region is not a risk factor for Alzheimer's disease related behavioral disturbances

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and often accompanied during its progression by behavioral and psychological symptoms of dementia (BPSD). We decided to evaluate the association between AD-related behavioral disturbances and the short/long (S/L) polymorphism of the promoter region of the 5-hydroxytryptamine (5-HT) transporter gene (SLC6A4). This functional polymorphism modulates SLC6A4 transcription rate, with the S-allele having a 2-fold reduced efficiency, leading to a diminished availability of 5-HT that might in turn trigger behavioral and cognitive alterations. The SLC6A4 promoter functional single nucleotide polymorphism rs25531 (A→G) was genotyped as well. We collected 235 sporadic AD subjects that were classified as AD with (n = 122) or without (n = 113) behavioral alterations, assessed with the Spontaneous Behavior Interview scale, section Behavioral Problems (SBI-BP). Comparing the genotypic and allelic frequencies of AD without and with BPSD, we did not find a difference for the 5-HTTLPR or the rs25531, even after stratification according to single SBI-BP item. We conclude that 5-HTTLPR and rs25531 are not major genetic modulators of BPSD development in AD.