ABGC Certification Examination (CGC credential) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Proband

The first person in a family through whom a genetic disorder comes to medical attention; marked with an arrow on a pedigree and used as the starting point for risk analysis.

Reduced penetrance

A situation in which some individuals carrying a pathogenic variant never express the associated phenotype, so an apparently skipped generation can still transmit the allele to offspring.

Variable expressivity

The range of type and severity of clinical features among individuals carrying the same pathogenic variant, ranging from subclinical signs to severe disease within one family.

Anticipation

Earlier onset or greater severity of a disorder in successive generations, classically seen with trinucleotide repeat expansions such as Huntington disease and fragile X syndrome.

Consanguinity

Mating between relatives; it increases the chance that both partners carry the same autosomal recessive allele and raises the risk of affected offspring.

Hardy-Weinberg carrier frequency

For a recessive disease with incidence q squared, carrier frequency is approximately 2 times the square root of q; for incidence 1 in 10,000, carriers are about 1 in 50.

Bayesian risk calculation

A method combining prior probability with conditional probabilities of observed events, such as unaffected children or negative test results, to yield a posterior recurrence risk.

Variant of uncertain significance

A genetic change whose link to disease is unproven; it should not be used to make clinical management decisions or to offer predictive testing to relatives without further evidence.

Incidental or secondary findings

Medically actionable variants unrelated to the original testing indication, such as BRCA1 or Lynch syndrome genes, which may be returned under an explicit opt-in consent policy.

Informed consent for genetic testing

The process covering test purpose, limitations, uncertain results, incidental findings, sample storage, privacy protections including the Genetic Information Nondiscrimination Act, and options for declining.

X-linked recessive inheritance

Pattern in which males are affected, no male-to-male transmission occurs, daughters of affected males are obligate carriers, and affected males have no affected sons.

Mitochondrial inheritance

Maternal transmission of mitochondrial DNA variants to all children, with males not transmitting further; heteroplasmy causes variable severity and threshold effects.

Uniparental disomy

Inheritance of both homologues of a chromosome pair from one parent, which can cause recessive disease when the parent is a carrier or imprinting disorders such as Prader-Willi syndrome.

Imprinting disorder

A disorder caused by abnormal expression of imprinted genes depending on parent of origin, such as Prader-Willi or Angelman syndrome from 15q11-q13 deletions or disomy.

Mosaicism

The presence of two or more cell lines with different genotypes in one individual, which can produce milder or asymmetric phenotypes and complicate recurrence risk estimates.

Germline mosaicism

A postzygotic variant confined to gonadal cells of a parent, producing affected children despite negative blood testing and a recurrence risk above the population baseline.

Prenatal cell-free DNA screening

A maternal blood test analyzing placental DNA fragments to estimate risk for common aneuploidies; it is a screening test requiring diagnostic confirmation by amniocentesis or chorionic villus sampling.

Chorionic villus sampling

Prenatal diagnostic procedure typically performed at 10 to 13 weeks, sampling placental tissue; it yields rapid results but carries a small miscarriage risk and does not detect neural tube defects.

Amniocentesis

Prenatal diagnostic procedure usually performed after 15 weeks, sampling amniotic fluid; results include karyotype, microarray, and alpha-fetoprotein for neural tube defects.

Preimplantation genetic testing

Testing embryos created by in vitro fertilization before transfer, used by couples at high reproductive risk to select embryos without a specific pathogenic variant.

Cascade screening

Systematic testing of at-risk relatives after a pathogenic variant is found in a proband, using the family-specific variant to identify carriers and offer risk-reducing care.

Genetic Information Nondiscrimination Act

United States law prohibiting health insurers and employers from using genetic information in coverage or employment decisions; it does not cover life, disability, or long-term care insurance.

Pathogenic variant classification

Assignment of a variant as disease-causing using evidence categories such as population frequency, computational prediction, functional studies, segregation, and de novo occurrence.

Genotype-first evaluation

A diagnostic strategy using exome or genome sequencing or chromosomal microarray before a specific syndrome is suspected, useful for atypical presentations and neurodevelopmental disorders.

Karyotype

A cytogenetic test visualizing chromosome number and large structural changes at roughly 5 to 10 megabase resolution; it detects aneuploidy, translocations, and large deletions or duplications.

Chromosomal microarray

A copy-number test detecting deletions and duplications at kilobase resolution; first-tier testing for developmental delay, intellectual disability, and autism spectrum disorder.

Trinucleotide repeat expansion

A mutation mechanism in which repeats lengthen across generations, causing anticipation; examples include Huntington disease, fragile X syndrome, and myotonic dystrophy.

Nondirectiveness

A counseling stance supporting patient autonomy by providing information and exploring values without steering the decision, while still responding to requests for guidance.

Psychosocial assessment

Exploration of patient understanding, emotions, family dynamics, cultural beliefs, and resources, guiding counseling and referral for psychological support when distress is significant.

Duty to warn

The question of whether a counselor may or must contact at-risk relatives about a hereditary condition; practice varies by jurisdiction and typically requires patient permission first.

Recurrence risk counseling

Communication of the probability that a condition will recur in a family, accompanied by explanation of the basis, uncertainty, and reproductive options available.

Newborn screening follow-up

Confirmatory testing and counseling after an abnormal newborn screen, recognizing false positives, carrier status, and the need for urgent treatment in disorders such as phenylketonuria.

Interpreter use in counseling

Working with a trained medical interpreter rather than a family member to ensure accurate communication of genetic risk, consent, and emotional content across language barriers.