10 - Genetic Screening and Diagnosis

Abstract

The goal of genetic screening is to identify individuals or couples at risk for having a child with an inherited condition, chromosome abnormality, or birth defect. Ideally, screening should take place before conception to ensure that couples are fully informed of their reproductive options, including preimplantation genetic screening and diagnosis, or screening should be done as early as possible in pregnancy to allow couples the opportunity to consider aneuploidy screening and prenatal diagnostic testing. Genetic screening begins with a thorough personal and family history, followed by genetic counseling if indicated. Approximately 3% of liveborn infants will have a major congenital anomaly; about one half of these anomalies are detected at birth and are due to a genetic cause: a chromosome abnormality, single-gene mutation, or polygenic/multifactorial inheritance. Less frequently, malformations may be due to nongenetic causes or teratogens. The detection of many congenital malformations is possible using ultrasonography and fetal echocardiography. Screening for aneuploidy, inherited disorders, and structural malformations is an integral part of routine obstetric care. When indicated and desired, amniotic fluid, placental tissue, and cord blood can be readily obtained and analyzed for chromosome abnormalities and genetic disorders. In this chapter, we review genetic history and counseling, common chromosome abnormalities, Mendelian disorders, aneuploidy and carrier screening, cytogenetic and molecular genetic testing, whole exome sequencing, and techniques for prenatal and preimplantation genetic diagnostic testing.