Painless Genetic Screening of Parents for Inheritable Disease now Available
The American College of Medical Genetics and the American College of Obstetrics and Gynecology have recently recommended that all couples of reproductive age who are attempting to conceive be offered pre-conceptual genetic testing. The purpose of this testing is to identify those couples who are carriers of a variety of conditions that could affect their children. Testing potential parents for genetic diseases is not a novel concept, but recent advances in technology have made testing simple, painless, and affordable.
“Carriers” of genetic diseases do not actually have the disorder themselves; rather one of their genes has a mutation, genetic change, associated with the disorder. The concern is that carriers can unknowingly pass this abnormal gene on to their children. The most common genetic disorders, such as Sickle Cell Anemia, Tay Sachs Disease, and Cystic Fibrosis are called “autosomal recessive” diseases. In order to actually have an autosomal recessive disease, a person needs to have inherited two abnormal genes, one from each parent.
In order to understand this concept, let’s look at Sickle Cell Anemia, a life threatening disease caused by abnormal hemoglobin. Each parent has 2 genes for hemoglobin – the important oxygen-carrying molecule in a red blood cell. All cells in the body – with the exception of sperm and eggs – carry 2 genes. Sperm and eggs carry only 1 of those 2 genes, and the one that they carry is determined at random. When fertilization occurs, the embryo gets one copy of the gene from each parent, i.e. one from the sperm and one from the egg. If each parent has two copies of the normal hemoglobin A gene, all of their sperm or eggs will be normal and their children will neither have Sickle Cell Disease nor will they be carriers. If one parent has one hemoglobin A gene and one hemoglobin S gene (the gene that causes Sickle Cell Anemia), each sperm or egg has a 50% chance of carrying the A gene and a 50% chance of carrying the S gene. Embryos that carry one S gene develop into children who are carriers. Therefore, in theory, 50% of children born to a carrier will be carriers for Sickle Cell disease.
If both parents are carriers, each embryo has a 25% chance of inheriting 2 A genes (i.e. those children will be normal), a 25% chance of inheriting 2 S genes (i.e. those children will have the disease), and a 50% chance of inheriting 1 A gene and 1 S gene (i.e. those children will be carriers).
Pre-conceptual testing is the only way to know if your children have an increased risk of inheriting a genetic disorder. Until recently, this could only be accomplished through the performance of individualized genetic tests, a very expensive and complicated process akin to looking for a needle in a haystack. Due to tremendous advances in genetic science, two new types of genetic testing are now available. One involves the collection of saliva from each partner. Each sample can be screened for over 109 different autosomal recessive genetic disorders for a reasonable fee. If only one partner is found to carry the gene for an autosomal recessive disorder, there is no chance that the couple’s children can actually have the disease in question; the worst outcome possible would be that a child could be an asymptomatic carrier of the abnormal gene – just like the affected parent. The primary advantages of this particular test are that it is performed on saliva rather than blood, it screens for a large number of diseases very efficiently, and it is relatively inexpensive.
The other type of test actually looks at pieces of genes, rather than whole genes or chromosomes. Through the testing of tissue obtained from either a cheek swab or blood from each partner, 200,000-300,000 small DNA fragments representing pieces of each known gene can be evaluated. When an embryo is produced from in vitro fertilization, the DNA from each embryo can be evaluated and matched to the samples from the parents. Not only can this testing determine whether each embryo has the normal number of chromosomes, but in addition the source of any identified genetic abnormality can be accurately identified. In other words, in the event that an embryo turns out to be chromosomally abnormal, this testing can determine whether the abnormality came from the egg or from the sperm. This is very helpful in cases of recurrent miscarriage or in cases of repetitive in vitro fertilization failure when couples are struggling to determine whether they should continue to proceed with treatment using their own gametes or whether they should consider using either donor sperm or donor oocytes.
These two exciting new technologies represent a major advance in the field of genetics and offer our patients even greater hope for achieving their dream of a healthy family.
For more information visit http://www.txfertilty.com
Originally from Dallas, Texas, Dr. Kaylen Silverberg received his undergraduate degree from Vanderbilt and attended medical school at Baylor College of Medicine. He completed his Obstetrics & Gynecology residency at Vanderbilt University Medical Center and his infertility fellowship at the University of Texas Health Science Center in San Antonio. Dr. Silverberg is actively involved in infertility research and has published extensively in the infertility literature. He was recently honored by the American Fertility Association with their National Family Building Award, and he is recognized annually by the Best Doctors in America, Best Doctors in Texas, and Best Doctors in Austin. Dr. Silverberg is Board Certified in both Obstetrics & Gynecology and Reproductive Endocrinology.