Examples of Genetic Testing Preconception and Prenatal Screening

Genetic screening or testing can occur either before conception or during the pregnancy. When possible, screening or testing before a pregnancy is ideal, because this provides the broadest range of choices if increased risk of a genetic defect is detected. Preimplantation genetic testing is available for

Table 44-3 Types of Genetic/Genomic Testing

Test

Example Methods

Clinical Scenarios

Example Conditions

Chromosomal analysis

Fluorescent in situ hybridization, karyotype, array comparative genomic hybridization

Pediatrics, prenatal testing

Down syndrome, unexplained mental retardation

DNA analysis

Allele-specific oligonucleotide hybridization, sequencing, fluorescent PCR assays, DNA microarrays

Adult, pediatric, prenatal testing, pharmacogenetic testing

Hereditary breast and ovarian cancer syndrome, Huntington's disease, cystic fibrosis, warfarin pharmacogenomics

Biochemical tests

Various

Adult, pediatric, prenatal

Hyperlipidemia, phenylketonuria, quadruple screen

Expression profiling

cDNA measurement on microarrays, quantitative PCR

Adult, pediatric

Breast cancer, melanoma, colorectal cancer

PCR, Polymerase chain reaction; cDNA, complementary (copy) deoxyribonucleic acid.

an increasing number of conditions but is costly and not accessible to many individuals. Most genetic evaluations occur after the pregnancy is established. The ability to detect genetic defects has grown rapidly over the past decade. Many ethical issues exist in both the preconception and the prenatal screening or testing environment, including the course of action if the fetus is found to have an incurable, life-altering condition. Common indications for prenatal testing are advanced maternal age, previous child with a chromosomal abnormality, family history of abnormality or single-gene disorder, family history of neural tube defect or other structural abnormality, abnormalities identified in pregnancy (e.g., on ultrasound), parental consanguinity, recurrent miscarriages, previous unexplained stillbirth, parental ancestral origin, and use of certain medications. The American College of Obstetricians and Gynecologists (ACOG) and the American College of Medical Geneticists (ACMG) have developed guidelines for recommended tests (Solomon and Feero, 2008). However, these guidelines are often based on consensus or expert opinion and do not always agree.

High-resolution ultrasound and quadruple serum panel are screening tests for congenital anomalies associated with a variety of genetic conditions. More invasive testing, such as chorionic villus sampling (CVS) and amniocentesis, may provide more accurate diagnosis, but at the cost of higher risk of complications. Recent guidelines suggest that amniocen-tesis be offered to all pregnant women to aid in the detection of Down syndrome (ACOG, 2007). The family physician should evaluate the risks and benefits of all forms of prenatal genetic screening or testing, discuss them with the patient and her partner, and make referrals to health care providers with genetics expertise as appropriate.

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