Intermediate alleles of HTT: A new pathway in longevity.

Centenarians are the best example of successful aging, reaching extreme longevity escaping age-related diseases. Genome sequencing studies provided evidence for genetic factors linked to heathy long life, including genes related to age-dependent diseases. HTT (Huntingtin) gene is linked to Huntington's Disease, but also associated to longevity in capuchins and mice. HTT Intermediate alleles (IAs) are defined as CAG repeat expansion between 27 and 35. According to recent data IAs might increase Alzheimer's Disease risk, but also might have a neuroprotective effect and can confer an advantage in brain development. Here, we investigated, for the first time, the possible implication of HTT IAs in extreme longevity and their possible association in cognitive decline. We analysed the distribution of IAs in Italian Centenarians (n = 143) and compared with pathological controls with cognitive decline (n = 232, including 80 Alzheimer's Disease, 78 Frontotemporal Dementia and 74 Subjective Cognitive Decline patients) and healthy controls (n = 104). Our data show a statistically significant higher frequency of IAs in Centenarians with respect to pathological controls with cognitive decline (p = .031; OR = 2.3097 95% CI 1.0591 to 5.0371), with a percentage of 11.2 respect to 5.4 respectively. The highest presence of IAs in Centenarians confirms and extends in humans a possible implication of HTT gene in exceptional lifespan and in brain development with a neuroprotective effect.