Human Genetic Screening
What is genetic screening? Genetic screening is the testing of cells to check for certain kinds of genes, or for potentially damaging changes to those genes. It may be defined as a systematic search for persons with a particular genotype in a defined population. Genetic screening serves as an important adjunct of modern preventive medicine. The usual approach is to identify persons whose genotype places them or their offspring at risk for genetic diseases. Such screening has the potential to lessen the devastating impact of genetic diseases. Genetic screening may be undertaken for research purposes unrelated to disease or the improvement of health. The National Academy of Sciences recommends that genetic screening is an appropriate form of medical care only when certain conditions are met. These include: (1) evidence of substantial public benefit and acceptance, (2) the benefits outweigh the costs; (3) appropriate public education can be carried out; (4) informed consent is feasible; (5) the means are available to evaluate the effectiveness and success of each step in the process (Blank, 1982). Some screening is aimed at the general population, while others are targeted at selective high-risk population; screening can also be conducted at various stages of life.
There are three principal types of genetic screening. (1) Newborn screening identifies serious genetic disease at birth, permitting prompt treatment to prevent mental and physical retardation. (2) Fetal screening and prenatal diagnosis identify genetic disease in the fetus permitting selective termination of pregnancy and the opportunity to have children free of defects detectable in uterus. (3) Carrier screening identifies individuals heterozygous for a gene for a serious recessive disease who may be at risk for having affected offspring.
(1) Newborn screening:
Newborn screening has focused on the detection of inborn errors of metabolism, which is an inherited biochemical defect, classically a deficiency of an intracellular enzyme. Phenylketonuria (PKU) is the first condition for which newborn screening was widely accepted. PKU may be due to phenylalanine hydroxylase deficiency or due to the deficiency of dihydropteridine reductase. High concentration of phenylaanine in the blood of a newborn may have multiple genetic and developmental causes. In general, before a newborn is discharged from the hospital, a sample of its blood is spotted onto filter paper and mailed to a regional laboratory equipped to monitor a large number of specimens rapidly and economically for these diseases. Newborn screening for PKU is a major triumph of genetic screening. Other inborn metabolic errors frequently screened for at birth are galactosemia, branch-chain ketonuria, homocystinuria, and hypothyroidism. Like PKU, these inborn errors may cause severe mental retardation or death which may be preventable by prompt treatment.
(2) Fetal screening and prenatal...