Texas Fertility, P.A.


Gene Abnormalities


A rare, but frequently devastating, reproductive problem for some couples is the birth of a child with an abnormal gene, causing a major, and even fatal, health problem.  The parents may not be affected, but are carriers for the disease.  In the case of carriers for the disease, each member of the couple has a single copy of an abnormal gene, and passes that abnormal gene in half the sperm and half the eggs.  Each child conceived from both a sperm with the abnormal gene and an egg with the abnormal gene will have the disease.  Those who receive only one abnormal copy of the gene will be carriers, like the parents.  Examples of these diseases include cystic fibrosis, sickle cell disease, Tay-Sach's, and thalacemia.  Currently, the American College of Obstetricians and Gynecologist is recommending that all couples considering having children be tested for their "carrier status" for cystic fibrosis.  This disease may cause life threatening lung problems, but may cause only a congenital absence of the vas deferens.  This is like being born with a vasectomy.

Other gene defects affect only male children, and are described as X-linked, since the gene is on the X chromosome.  Women have a pair of X chromosomes, and men an X and a Y.  In the case of a male inheriting an abnormal gene on an X chromosome from his carrier mother, there is not a normal copy of the gene from his father, to balance the abnormal gene.  Some examples of X-linked diseases are color blindness, hemophilia, and muscular dystrophy.  In addition to X-linked disease, some other genetic abnormalities are expressed with only a single copy of an abnormal gene inherited from only one parent.

Today, there are technologies available to help prevent these diseases. Some of the processes are fairly new, and not yet proven to be completely reliable, but seem to be useful tools.  One of these tools, which we can use to help the couple with congenital absence of the vas deferens, is to extract sperm from the epididymis, and inject these immature sperm into the eggs of the wife, in an IVF process.  First, the wife should be tested to be sure she is not a carrier for cystic fibrosis.  If she is, one quarter of their children will have cystic fibrosis, which could be worse than the father's disease.

In addition to being able to create embryos where none could exist otherwise, we also have the ability to do diagnostic studies on embryos.  After an embryo is created, and grown in the lab for 3 days, a single cell from the embryo (a blastomere), can be studied for the gene defects, already identified in the parents.  This form of molecular pre-implantation genetic diagnosis was first performed in 1991, for a couple who had two sons with severe lung disease caused by the cystic fibrosis gene.  Other single gene defects can, now, be diagnosed in the embryo.  Once the diagnosis is made, only the unaffected embryos are placed in the uterus, to avoid having a child with the disease.

Obviously, the couple seeking pre-implantation genetic diagnosis (PGD) requires IVF.  The IVF facility will need to collaborate with a special genetics laboratory, capable of testing the blastomeres, and providing a reliable report to the IVF program within two days.  There are only a few genetics facilities in the country capable of providing the service.  The blastomeres will have to be shipped to the lab where the molecular studies are to be done.  The process, including IVF, costs several thousand dollars, but for some couples, it may be worth the expense, effort, and stress.


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