Prevalence of frontotemporal lobar degeneration in an isolated population: the Vallecamonica study

The study of neurodegenerative diseases, such as frontotemporal lobar degeneration (FTLD), in isolated populations represents a privileged point of view for identifying new causative genes and pathogenetic mechanisms. Vallecamonica is a valley located in the Brescia province (Northern Italy), which experienced isolation until the end of World War II. The aims of the present work were (1) to estimate the prevalence of FTLD in Vallecamonica, (2) to determine the monogenic FTLD forms, and (3) to identify FTLD cases with no evidence of known pathogenetic mutations and the related clinical features. Patients meeting current clinical criteria for FTLD were considered. Mutation analysis for microtubule associated protein tau (MAPT) and progranulin (PGRN) genes was performed, as well as serum PGRN dosage. On the census day, 42 FTLD patients were alive, resulting in an overall disease prevalence of 35 per 100 inhabitants. Thirty-one out of 42 patients underwent sequencing analysis. Five patients carried PGRN Thr272fs mutation and one patient MAPT P301L mutation. There were no differences in term of age at onset and gender between this group and mutation carriers, but the latter had greater family history for dementia (100%, P = 0.01). In Vallecamonica, we detected a higher prevalence of FTLD compared with that already reported in other populations. A founder effect or a genetic drift might be considered for an allelic enrichment. Ongoing study aims to identify the presence of a new genetic form in those FTLD patients without known pathogenetic mutations in this isolated population.