Genetics play a central role in fertility, particularly since sperm carry half of the DNA mix to the partner's egg. Abnormalities in chromosomal numbers and structure as well as deletions on the important Y chromosome present in normal males can also impact fertility.
Genetic abnormalities can be a cause of a low sperm count and or weak sperm. Parents, who have a family history of genetic abnormalities, should address the issue before having children. Pre-implantation Genetic Diagnosis (PGD) can be a lifesaving tool to assure that only normal embryos are transferred.
Main categories of genetic abnormalities that affect sperm and embryos include:
GENETIC ABNORMALITIES THAT EFFECT MALE FERTILITY
1. Microdeletions or abnormalities of the Y-chromosome can be the cause for low sperm concentrations (less than 5million/ml).
2. Single gene disorders: infertility is a common sideeffect of many genetic disorders which include Cystic Fibrosis (CF) and Polycystic Kidney Disease, Klinefilters syndrome, Down ’s syndrome etc. Men who are carriers of the CF gene may have incomplete vas deference. This means that even though normal sperm are produced, there is no intact pathway to get these sperm to the outside. Testicular or epididymal sperm extraction with ICSI and IVF is necessary to join the sperm and egg. One or both intended parents may be a carrier of certain single gene disorders, which can result in affected embryos.
GENETIC ABNORMALITIES PRODUCE DEFECTIVE EMBRYOS
1. Translocation. This is where the embryo has too much or too little of a specific chromosome. This typically is presented as an inability to conceive or as a recurrent miscarriage.
2. Incorrect number of chromosomes such as Down’s and Edward Syndrome, or embryos with multiple chromosomal imbalances (aneuploidy), which prevent development after the 8-cell stage.