Genetic Screening and Counseling

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Basics

Description

  • Rapid advances in elucidating the genetic basis of disease have resulted in the need for both primary care and specialty physicians to perform genetic risk assessment in their practices and refer patients for genetic counseling when indicated.
  • Genetic counseling is the process of communicating information about genetic risks. It focuses on susceptibility to disease in individuals who are
    • Suspected of having a heritable disease
    • At risk due to family history
    • Concerned about affected offspring due to family history, age, or ethnicity
  • Genetic counseling is provided in a nondirective manner, free of bias and coercion, thus empowering individuals or families to make well-informed decisions about their health care.
  • Genetic screening is performed on a population of individuals potentially at risk for the condition under consideration. Definitive diagnostic testing or confirmation follows a positive or indeterminate result. Individuals who have been identified by screening may receive genetic counseling to explain the implications of a positive screening result and the need for further diagnostic testing.
    • Counselors may assist clinicians and patients in choosing or declining various screening or diagnostic tests.
    • Pregnancy considerations: Genetic counseling may address elevated genetic risks associated with maternal age, family history of heritable genetic disease, teratogenic exposures, prenatal screening results suggestive of increased risk, or abnormal findings on prenatal ultrasound.
    • Newborn screening: varies by state according to the genetic makeup of the population. Conditions screened are those for which there is an effective treatment that can make a clinically significant difference.
    • Pediatric considerations: Genetic counselors work with pediatric specialists including medical geneticists to evaluate children at risk for a chromosomal abnormality or genetic syndrome because of developmental delays, intellectual disabilities, certain genetic-based medical problems, and/or dysmorphic features. Children should not be tested for adult-onset conditions for which there is no treatment in childhood.
    • Geriatric considerations: Genetic counseling and screening may be indicated to assess genetic predisposition for individuals and family members for conditions common in elderly populations.

Epidemiology

Incidence
Recognizable genetic disease will be diagnosed in 3–7% of the population at some point during their lifetime.

Prevalence
  • Chronic medical illnesses such as diabetes, heart disease, cancer, and Alzheimer disease have a genetic basis in up to 10% of cases.
  • 50% of pediatric hospital deaths are associated with genetic diseases.
  • Congenital malformations are identified in 2–5% of newborns.

Etiology and Pathophysiology

Genetic disorders are classified into four major etiologies:

  • Chromosomal disorders
  • Single gene disorders
  • Multifactorial disorders
  • Mitochondrial disorders
Genetics
  • Patterns of transmission include the following:
    • Autosomal recessive
    • Autosomal dominant
    • X-linked
    • Mitochondrial/maternal
  • De novo mutations, incomplete penetrance, and variable expressivity may obscure the nature of inheritance, which can lead to variable presentations of many conditions.
  • Many cancers have one or more disease-causing mutations. Identification of a specific mutation can guide choice of therapy.

Risk Factors

  • Identification of genetic risk may allow tailored interventions, lifestyle changes, and disease-prevention strategies.
  • Family history of genetic disease
  • Consanguinity
  • Ethnic or racial background (see “Diagnostic Tests & Interpretation”)
  • Abnormal pregnancy screening tests
    • Aneuploidy screening
    • Abnormal ultrasound results
    • Abnormal screening results for cystic fibrosis, ethnicity-based inherited genetic disease, or other positive carrier screening

General Prevention

  • Genetic conditions cannot be prevented under ordinary circumstances (preimplantation diagnosis or prenatal diagnosis and pregnancy termination may be possible when a specific risk is known).
  • Diet or behavior can be modified to minimize or modify the clinical severity of some conditions (e.g., phenylketonuria and low-phenylalanine diet).

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