Late-onset Alzheimer’s disease (LOAD) can occur sporadically or be inherited. In the inherited disorder, there is evidence of maternal inheritance in more than 20% of cases. The pattern is consistent with mitochondrial inheritance. Previous studies have observed decreased glucose metabolism and atrophy in brain regions affected in Alzheimer’s disease; progressive gray matter atrophy has only been observed in people with a maternal family history of Alzheimer’s. These same individuals had greater atrophy in the precuneus and parahippocampal gyrus (regions known to be affected in Alzheimer’s) than those with a paternal or no family history of Alzheimer’s. The role of specific mitochondrial DNA (mtDNA) variants and haplogroups is not clear.

The present study investigated mitochondrial DNA sequences in 1,007 patients with late-onset Alzheimer’s disease. Two mitochondrial haplotypes, H6A1A and H6A1B, were found to be associated with a reduced risk of late onset Alzheimer’s disease.

This is the largest study to date with complete mitochondrial DNA genome sequence data, but the functional significance of the associated haplotypes remains unknown. Further research investigation is recommended by the authors of this study.

Ridge PG, Maxwell TJ, Corcoran CD, Norton MC, Tschanz JT, O’Brien E, Kerber RA, Cawthon RM, Munger RG, Kauwe JS:  Mitochondrial Genomic Analysis of Late Onset Alzheimer’s Disease Reveals Protective Haplogroups H6A1A/H6A1B: The Cache County Study on Memory in Aging.  PLoS One 7(9): e45134 (2012). doi: 10.1371/journal.pone.0045134.

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