Carrier Screening for Genetic Conditions
Testing for many genetic diseases is now possible due to the advancement in genetic technology. The inheritance pattern of genetic disease can be broadly categorized into autosomal dominant, autosomal recessive or X-linked. Patients with an autosomal dominant or X-linked disorder will usually have an affected family member that may prompt genetic testing. Autosomal recessive disorders may be “silent” and not manifest until a person reproduces with someone who also carries the recessive gene. The risk of having an affected child if both parents are carriers is 25%. Carriers of an autosomal recessive gene usually do not have any symptoms of the disease. The carrier rate depends on the disease in question and the ethnicity of the individual. Carrier screening refers to genetic testing of a person who has no signs of a genetic disorder, but who could be a carrier of a recessive gene for a disorder.
It is not recommended, nor is it practical, to screen for all possible genetic disorders. The most common recessive genetic disorders that a person might be a carrier of include the following: cystic fibrosis (CF), spinal muscular atrophy (SMA), fragile-x syndrome and the hemoglobinopathies, which include sickle cell disease and thalassemias. The carrier rate for CF is 1:25 in Caucasians, 1:61 in African Americans, 1:58 in Hispanics and 1:94 in Asian Americans. The carrier rate for SMA is 1:35 in Caucasians, 1:66 in African Americans, 1: 117 in Hispanics and 1:53 in Asian Americans. Sickle cell trait is found in 1:10 African Americans. The fragile-x mutation is found in 1:86 women with a family history of a mental disability and 1:257 in women without such a history. Thalassemias are found more commonly in individuals of Southeast Asian, African, Mediterranean, Middle Eastern, West Indian and Hispanic heritage. Individuals of Ashkenazi Jewish heritage are at increased risk for Tay-Sachs disease, Bloom’s syndrome, Canavan disease and familial dysautonomia, among others.
If a person is found to be a carrier of one of these genetic diseases, it is recommend that the partner be screened. Alternatively, both partners can be screened simultaneously. A negative carrier screen greatly decreases the chance of being a carrier, but does not completely eliminate it. This “residual risk” is a function of the disease tested and the ethnicity of the individual. Genetic carrier screening ideally should be performed prior to pregnancy. The purpose of carrier screening is to identify patients at risk for having an affected child and allow them to make informed decisions about their reproductive options.
Arkansas Fertility & Gynecology recommends that all patients seeking fertility treatment consider whether or not they would like to have genetic carrier screening performed. Testing is optional and does not affect your ability to receive care at this clinic. Insurance does not always cover testing in which case you would be responsible for the cost. We use Integrated Genetics as our genetic labs. Integrated Genetics (www.integratedgenetics.com/patients/pre-pregnancy) will check your insurance coverage and let you know how much the testing will cost you. Genetic counsellors are available and can discuss both positive and negative screening results with you. The physicians at Arkansas Fertility & Gynecology can also discuss this with you and your partner.