18 Oct The role of genetics in the reproductive process
Infertility is a complex disease and can be caused by different factors including ovulation defects, spermatogenic failure, parental age, obesity, infections, uterine abnormalities, endometriosis and genetic abnormalities. The role of genetics in the reproductive process it’s very important.
Genetic infertility causes can affect both men and women and can be divided into two major groups : cytogenetic anomalies and gene defects.
Cytogenetic anomalies and infertility
Couples with infertility have higher risk of having abnormalities in their chromosomes that general population. The abnormalities can be classified in:
- Numerical: extra or missing chromosomes. For example, Klinefelter syndrome in males (karyotype XXY). Klinefelter men have an extra chromosome X usually suffer from azoospermia (no spermatozoa) and can benefit from testicular sperm retrieval from microdissection testicular sperm extraction (TESE). Another example is Turner syndrome in females (karyotype X0 with a missing chromosome X). Most women with Turner’s syndrome have ovarian dysgenesis and they are usually infertile.
- Structural: they do not usually affect the health of the carrier, but they are frequently related to infertility and recurrent miscarriages. This is because the carriers of this abnormalities can produce abnormal eggs or sperm (with missing or extra parts of chromosomes). This eggs and sperms can in some cases fertilize to produce a developing embryo that achieve pregnancy. But the abnormalities in the embryo can lead to a miscarriage or an baby born with severe malformations. This couples can benefit from an IVF cycle with Preimplantation Genetic Testing (PGT-SR) to achieve pregnancy and have a healthy baby.
Karyotype analysis in blood is nowadays strongly recommended in all couples prior to any assisted reproduction procedure in order to detect this anomalies and offer them proper counselling.
Single gene defects and infertility
There are a lot of different single gene defects that can cause fertility problems. Some examples of them are:
- Y chromosome microdeletions in male: there is one region of chromosome Y especially relevant for the production of sperm. Abnormalities in these region can cause oligozoospermia (low sperm count) and azoospermia.
- CFTR gene mutations in males: Males with one mutation in CFTR gene can present infertility. CFTR mutations cause congenital bilateral absence of vas deferens or sperm abnormalities such as azoospermia, teratospermia, and oligospermia.
- FMR1 gene mutations in females: Women with abnormalities in gene FMR1 can suffer from Premature ovarian failure, that is the onset of menopause in women under the age of 40 years.
Genetic tests are part of the diagnostic workup of the infertile couple and may contribute to the clarification of the cause in some cases. A proper diagnosis can help to counsel the couple about its reproductive choices and to offer the best and most suitable treatment to achieve pregnancy in each case.