Male infertility comprising low sperm number (oligozoospermia), with loss of sperm motility (asthenozoospermia) is a common phenotype in humans, and has been reported, in specific populations, in individuals polymorphic for the CAG repeat at the POLG1 (mtDNA polymerase) locus (63,64), or deriving from a specific mitochondrial haplogroup (65). Here, POLG is linked to Reduced sperm motility.