Do haplogroups H and U act to increase the penetrance of Alzheimer's disease?

1. Alzheimer's disease (AD) is the most common form of dementia in the elderly in which interplay between genes and the environment is supposed to be involved. Mitochondrial DNA (mtDNA) has the only noncoding regions at the displacement loop (D-loop) region that contains two hypervariable segments (HVS-I and HVS-II) with high polymorphism. mtDNA has already been fully sequenced and many subsequent publications have shown polymorphic sites, haplogroups, and haplotypes. Haplogroups could have important implications to understand the association between mutability of the mitochondrial genome and the disease.2. To assess the relationship between mtDNA haplogroup and AD, we sequenced the mtDNA HVS-I in 30 AD patients and 100 control subjects. We could find that haplogroups H and U are significantly more abundant in AD patients (P = 0.016 for haplogroup H and P = 0.0003 for haplogroup U), Thus, these two haplogroups might act synergistically to increase the penetrance of AD disease.