Certain genetic conditions may affect fertility or may be treated through a variation of in vitro fertilization (IVF). In general, these genetic abnormalities fall into two categories: Single gene defects and chromosomal abnormalities.
Single gene defects involve a mutation or abnormality within the DNA which codes for a particular gene. Single gene defects can lead to health conditions that can cause fertility problems. These conditions include cystic fibrosis, Tay Sachs disease, spinal muscular atrophy, Canavan disease, sickle cell disease, and Thalassemias.
Chromosomal abnormalities include changes in the number or structure of the chromosomes which carry the DNA. These changes often affect many genes. The normal number of chromosomes for humans is 46. Women have 22 pairs of autosomes and two X chromosomes. Men have 22 pairs of autosomes and one X and one Y chromosome.
Examples of chromosomal abnormalities include Down syndrome (Trisomy 21—an extra chromosome 21), Turner syndrome (loss of one X chromosome) and Klinefelter syndrome (an extra X chromosome in men).
In men, chromosome abnormalities can be associated with low sperm counts. Y-chromosome gene deletions and cystic fibrosis gene mutations may be associated with azoospermia or a lack of sperm. Cystic fibrosis gene mutations also may result in an absence of the ducts that transport sperm. Genetic testing is recommended for all men with a lack of sperm (azoospermia) or low sperm counts.
In women, chromosomal abnormalities can be associated with pregnancy loss or even clinical conditions in children such as Down syndrome.
Some genetic conditions that affect fertility occur more frequently in certain populations: Tay Sachs disease (Ashkenazi Jews and French Canadians), Canavan disease (Ashkenazi Jews), sickle cell disease (African Americans, Hispanics and Mediterraneans), and Thalassemias (Mediterranean, Middle East and East Asians). CIRS physicians may suggest genetic tests for single gene defects as part of the initial infertility evaluation, especially if either partner is from one of these ethnic groups or if a partner has a family history of certain diseases such as cystic fibrosis.
A history of recurrent miscarriages also would require chromosomal testing of both partners.
Should a genetic or chromosomal abnormality be found during your evaluation, your physician may recommend genetic counseling in which a detailed family genetic history is obtained and an assessment of risk determined. Preimplantation genetic diagnosis (PGD) or preimplantation genetic screening may be performed to screen embryos for genetic conditions before implantation. PGD involves the removal of one or two cells from an embryo on Day 3 or Day 5, and genetic analysis of the biopsied cell(s).