Large Scale 7436-bp Deletions in Human Sperm Mitochondrial DNA with Spermatozoa Dysfunction and Male Infertility

Mitochondria and mitochondrial DNA are essential to sperm motility and fertility. It controls growth, development and differentiation through oxidation energy supply. Mitochondrial (mtDNA) deletions or mutation are frequently attributed to defects of sperm motility and finally these deletions lead to sperm dysfunction and causes infertility in male.

To investigate the correlation between large scale 7436-bp deletions in sperm mtDNA and non-motility of sperm in asthenozoospermia and Oligoasthenoteratozoospermia (OAT) infertile men.

The present prospective study was carried out in Human Genetic Division, Department of Anatomy, Mahatma Gandhi Institute of Medical Sciences, Sevagram from June 2014 to July 2016. We have studied 110 asthenozoospermia and OAT infertile men whose semen profile indicated abnormal motility and 50 normal fertile controls. Of 110 infertile men, 70 had asthenozoospermia and 40 had OAT. Fractionations of spermatozoa were done in each semen sample on the basis of their motility by percoll gradients discontinuous technique. Long-range PCR was used for detection of 7436-bp deletions in sperm mtDNA and was confirmed by primer shift technique.

Overall eight subjects (8/110; 7.2%) of which six (6/70; 8.57%) asthenozoospermia and two (2/40; 5%) OAT had shown deletions of 7436-bp. In 40% percoll fraction had more non-motile spermatozoa than 80% percoll fraction. The non-motile spermatozoa in 40% percoll fractions showed more mtDNA deletions (7.2%) than the motile spermatozoa in 80% percoll fraction (2.7%). The sequencing of flanking regions of deleted mtDNA confirmed 7436-bp deletions. Interestingly, no deletions were found in control subjects.

Though, the frequency of 7436-bp deletions in sperm mtDNA was low in infertile cases but meaningful indications were there when results were compared with controls. It is indicated that large scale deletions 7436-bp of mtDNA is associated with abnormal sperm motility. The 7436-bp deletions of mtDNA in spermatozoa may be one of the important causes of dysfunction and non-motile sperm.