Genetic Screening

It is estimated that everyone is a carrier for approximately 8 to 10 non-working genes (mutations) that could be of significance to future children. The availability of screening for the most common genetic disorders allows us to identify couples who have a greatly increased chance of having a child with a specific disorder and offer further reproductive options. Optimally, this screening is performed prior to pregnancy so that couples have the option of preimplantation genetic testing (PGT), in addition to CVS and amniocentesis. PGT allows couples to avoid facing the difficult decision of whether or not to continue an affected pregnancy. Some common conditions for which screening is available are described below, however, our collaborators around the country can usually develop individual tests for other single-gene disorders.

Cystic Fibrosis

Cystic Fibrosis (CF) is an inherited condition that causes the body to produce unusually thick, sticky mucus which results in chronic lung infections and digestive problems. CF is inherited in an autosomal recessive manner, meaning that both parents must be carriers of one defective gene to be at risk to have a child with CF. Caucasians have the greatest chance to be a carrier for cystic fibrosis (1 in 25). People from other ethnic backgrounds can also be carriers; however, their chance to be a carrier is less than 1 in 25. Genetic carrier screening is available to determine if someone is a carrier for CF. Carrier screening reduces but does not eliminate the risk that a person is a carrier for CF. If both parents are found to be carriers there is a 25% (1 in 4) chance to have a child with CF. In this case, options such as preimplantation genetic testing (PGT) and prenatal diagnosis are available.

Hemoglobinopathies

Hemoglobinopathies are a group of disorders that result in abnormal hemoglobin which causes anemia. Examples of hemoglobinopathies include sickle cell disease, beta thalassemia and alpha thalassemia. Hemoglobinopathies are also inherited in an autosomal recessive fashion. Those at an increased risk to be a carrier of a hemoglobinopathy are individuals of Asian, Asian Indian, Mediterranean, Middle Eastern, African American and Hispanic descent. Carrier screening is available to determine if an individual is a hemoglobinopathy carrier. If these tests are normal, a person is not considered to be a carrier and would have a low risk to have a child with a hemoglobinopathy. If both parents are found to be carriers there is a 25% (1 in 4) chance to have a child with a hemoglobinopathy. In this case, options such as preimplantation genetic testing (PGT) and prenatal diagnosis are available.

Ashkenazi Jewish Screening

Individuals of Ashkenazi Jewish descent (Eastern European Jewish) are at an increased risk to be a carrier of several conditions. If both parents are found to be carriers of a certain condition, there is a 25% (1 in 4) chance to have a child with that condition. In this case, options such as preimplantation genetic testing (PGT) and prenatal diagnosis are available. Negative carrier screening significantly reduces, but does not eliminate the possibility to be a carrier. Carrier screening is available for 11 different diseases whose carrier frequencies are increased in the Ashkenazi Jewish population. The conditions and their carrier frequencies are listed below:

Spinal Muscular Atrophy Screening

Spinal Muscular Atrophy (SMA) is an autosomal recessive inherited disease caused by the loss of motor nerve cells in the spine and brain. This not only causes muscle weakness throughout the body, but also muscle wasting and even paralysis. There are several types of SMA that differ in the age when symptoms begin and whether the symptoms are severe or mild. Although SMA most often affects a baby less than two years of age, some patients develop symptoms before birth and some as late as adulthood. SMA is found in all ethnic/racial groups around the world. The chance to be a carrier can vary based on ethnic background. For example, individuals of Caucasian descent have a 1 in 35 chance to be a carrier and individuals of African American descent have a 1 in 66 chance to be a carrier. Presently, SMA carrier screening is recommended by the American College of Medical Genetics (ACMG), but not the American College of Obstetrics and Gynecology (ACOG), for all patients considering pregnancy or who are currently pregnant. A negative SMA carrier screening result significantly reduces, but does not eliminate the chance that an individual is a SMA carrier. If both parents are found to be carriers there is a 25% (1 in 4) chance to have a child with a SMA. In this case, options such as preimplantation genetic testing (PGT) and prenatal diagnosis are available.

References

Ancestry Based Carrier Screening. National Society of Genetic Counselors, Inc. Publication of the Prenatal Special Interest Group. 2005.

American College of Obstetricians and Gynecologists, American College of Medical Genetics. Preconception and Prenatal Carrier Screening for Cystic Fibrosis: Clinical and Laboratory Guidelines. Washington, DC: ACOG; Oct 2001.

American College of Obstetricians and Gynecologists.Genetic Screening for Hemoglobinopathies. Committee Opinion. Washington, DC: ACOG; July 2000. Number 238.
Gross et al., Genetics in Medicine 10:54-56, 2008

Obstetrics and Gyneology 104:425, 204: Committee Opinion 298
Spinal muscular atrophy. ACOG Committee Opinion No. 432.American College of Obstetricians and Gynecologists.Obstet Gynecol. 2009; 113:1194–6.