The first of the three tests is Cell-free DNA testing. In this test, the mother's blood is screened to detect the DNA from the fetus and looks for common chromosomal disorders (like Down Syndrome or Wolf-Hirschhorn syndrome). This test has a higher detection rate and a few false-positives. “Prior to this new test, mothers had the option of traditional first trimester screening, which is a blood test and ultrasound, or second trimester screening, which is a blood test. In general, the cell free DNA blood test can be used in place of the traditional first and second trimester screening,” explains Dr. Wick.
In an Expanded Carrier Screening, a blood test is done on each prospective parent prior to the conception of their child. In the past, couples who had a genetic screening could only be assessed based on history of known familial genetic diseases and risks based on their respective ethnic groups. Obviously, these tests were limited in scope and could not help parents that were not sure of their ethnic group or family history (such as an adopted child). However, with the new screening, prospective parents can take a more comprehensive test that looks at over 100 different diseases and disorders. Dr. Wick explains that the tests look at multiple genes associated with a genetic disorder and takes into account recessive autosomal inheritance, "A child is affected with an autosomal recessive disorder when he or she inherits one abnormal copy of the gene from mom, and one abnormal copy of the gene from dad. Approximately 5% of couples who undergo expanded carrier screening are found to be carriers for the same disorder, and at risk for having an affected child."
In extreme cases where the baby has been identified with several medical problems, a Whole Exome Sequencing can take place. With a WES test, the genes and proteins associated with growth and health can be used to asses the fetus's condition. Dr. Wick explains that “We are beginning to use WES even before the baby is born. Results can be used to plan for care of an infant who may be born with several complex medical concerns. In addition, parents can use this information for future family planning."As the human genome becomes better understood, it is becoming increasingly important for prospective or expectant parents to seek out a genetic counselor that can interpret genetic tests and help with family planning based on genetic risk.
False positives and false negatives are always a concern in science. It's great to hear that there is improvement in prenatal screenings to reduce these type I and type II errors.ReplyDelete