MALATTIA DI ALZHEIMER E DEGENERAZIONE LOBARE FRONTOTEMPORALE: RICERCA DI MUTAZIONI AUTOSOMICHE DOMINANTI E ANALISI GENETICA E FUNZIONALE DI GENI CANDIDATI

This PhD study is intended to perform a genetic screening on a population of AD and FTLD patients in order to identify pathogenetic causal mutations (PSEN1, PSEN2 and APP for AD; MAPT, GRN and the GGGGCC repeat expansion one the C9orf72 gene for FTLD) and to investigate the role of several candidate genes (GRN,TMEM106b and OLR1) considered to be risk factors for the two disease. Eighteen patients were carriers of pathogenetic causal mutations: 1 carrier of Ala260Val (g.49964C>T) situated in exon 8 of PSEN1,16 carriers of GRN gene mutations and 1 carrier of a new variant, Gly304Ser (g.123789G>A), located in exon 10 of MAPT gene. The presence of GGGGCC repeat expansion, positioned on the first intron of C9orf72 gene, was analyzed in a larger population (651 FTLD patients, 21 CBD and 31 PSP patients). Thirty nine patients with FTLD were carriers of pathogenetic repeat expansion, whereas none of CBD and PSP patients as well as 222 controls carried the mutation. Several associations studies were performed in the remaining sporadic population of AD and FTLD patients. Regarding the influence of GRN genetic variability on susceptibility to AD, two SNPs rs9897526G>A and rs5848 were investigated. A tendency to an increased frequency of rs5848T allele was found in AD patients as compared with controls, whereas for the rs9897526 SNP, in patients carrying the rs9897526A variant was observed a significant earlier age at disease onset compared with patients carrying the G allele. The case-control study carried out on a populations of FTLD patients was focused on four Tagging SNPs (rs2879096, rs3785817, rs4792938 and rs9897526) as well as on rs5848 SNP, localized in the 3’UTR of GRN gene. A statistically significant association of the rs4792938 CC genotype was observed in FTLD patients compared with healthy controls. Concerning the role of TMEM106b gene on susceptibility to AD, an association analysis was performed on three SNP, rs1020004 A/G, rs6966915 C/T and rs1990622 A/G, but no significant differences in allelic and genotype frequencies were found for all polymorphisms between AD patients and controls. The possible functional importance of genetic variability associated with this gene was tested by plasmatic ELISA detection of GRN on eighty AD patients. Stratifying the results according to rs1990622 SNP status, no significant differences in progranulin plasma levels were found in AD patients. Regarding OLR1, in particular it was analyzed the SNP rs1050283 T/C, located in 3’UTR of the gene. Logistic regression analysis, adjusted for gender and ApoE status, showed a statistically significant association of OLR1 rs1050283 under the assumption of a dominant and a genotypic model. Therefore this SNP could be considered a susceptibility factor for sporadic AD. Given that the SNP rs1050283 is also located in a predicted binding site of the miRNA has-miR369-3p, a preliminary expression analysis was performed on the two transcripts in the PBMC in order to clarify a possible functional role of individual genetic variability on the expression of OLR1 gene. Stratifying the results according to the presence of rs1050283C allele, a significant decrease of relative expression levels of OLR1 was observed in patients carrying at least one polymorphic C allele, despite the normal expression levels of has-miR369-3p. These data suggest that the presence of the polymorphic allele could influence the binding of has-miR369-3p to its 3’UTR consensus sequence, in which the SNP is located.