PPARGC1A and Huntington disease: Recently, mitochondrial DNA (mtDNA) haplogroup H (7028C) and variations in the peroxisome proliferator-activated receptor gamma coactivator 1a (PPARGC1A) gene encoding PGC-1alpha were shown to exert modifying effects on the AO in HD, thus providing genetic evidence that complex interrelations of mitochondrial dysfunction have effects on the pathogenic process in HD [11-14].