doi:10.1038/nindia.2012.165 Published online 15 November 2012
Researchers in New Delhi have identified the genetic reasons why some men are infertile despite having a normal "spermiogram" with enough number of sperms that are motile and viable. The findings will augment DNA diagnosis, proving beneficial for those engaged in in-vitro fertilization (IVF), genetic counseling and assisted reproduction technology (ART) .
Human infertility affects about 15% people in the reproductive age group globally with men accounting for half of this. Male fertility is an orchestrated interplay of loci — or DNA sequences — on the Y chromosome with a number of genes from across other chromosomes. Micro-deletions in the Y chromosome have been linked to poor sperm counts often leading to infertility but causes of infertility in patients with normal spermiogram have so far remained unclear.
To find out the causes, the researchers studied 31 infertile males having normal spermiograms. Routine semen analyses found all of them to be normal suggesting that unknown factors were behind infertility in these patients. To pinpoint these factors, they conducted "Single Nucleotide Variant" analyses of the three regions referred to as 'azoospermia factors' and the 'DYZ1 region' of the Y chromosome of these infertile men. They found new mutations not observed in normal fertile males used as controls.
"This work demonstrates that infertility in the human males having normal spermiogram is caused due to aberrations of the several Y chromosome linked genes and loci including DYZ1 region (that constitutes approximately 40% of the Y-chromosome)," the researchers report. Therefore, semen samples should be "checked for all the possible candidate genes and loci for their normal status" and the Y-chromosome analyzed for micro-deletions before using them for IVF and ART, the study concludes.