ABGC Certification Examination (CGC) flashcards

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

Proband

The first affected family member who brings the family to medical attention; marked with an arrow on a pedigree and used as the starting point for risk assessment.

Variants of uncertain significance

Sequence changes with insufficient evidence to classify as pathogenic or benign; they should not be used to make clinical management decisions and may be reclassified over time.

Informed consent elements

Counselor documents test purpose, genes analyzed, detection limits, possible VUS and incidental findings, cost, and implications for relatives before sample collection.

Autosomal recessive recurrence risk

For two confirmed carrier parents, each pregnancy carries a 25% affected risk, 50% carrier risk, and 25% unaffected non-carrier risk, independent of prior pregnancies.

Autosomal dominant recurrence risk

An affected heterozygote with an affected partner-free mating transmits the allele to 50% of offspring per pregnancy; unaffected offspring of a fully penetrant dominant condition are generally not at risk.

X-linked recessive transmission

Carrier mothers pass the allele to half of sons (affected) and half of daughters (carriers); affected fathers transmit to all daughters and no sons.

Bayesian analysis

A method combining a prior probability with conditional probabilities from test results or unaffected status to calculate a posterior risk for a consultand.

Pedigree documentation standards

Pedigrees should record at least three generations, ages, affected status, consanguinity, ethnicity, pregnancy outcomes, and the date the pedigree was taken.

Family letter

A patient-mediated written communication summarizing the genetic finding and recommended relative testing; it omits the patient's identifying details and is documented in the record.

Pretest counseling

A structured discussion of the reason for testing, test characteristics, potential results including uncertainty, cost and insurance issues, and the plan for disclosure.

Results disclosure session

A visit that communicates variant classification, clinical implications, management recommendations, and relative testing options, with documentation of the patient's decisions.

Reproductive risk options

Options after identifying elevated risk include prenatal diagnosis, preimplantation genetic testing, gamete donation, adoption, and accepting the risk; each is presented non-directively.

Non-directive counseling

A practice stance in which the counselor provides information and support while the patient makes the decision, avoiding steering toward a particular reproductive or testing choice.

Red flags for referral

Early-onset cancer, multiple affected relatives, bilateral or multifocal tumors, congenital anomalies, developmental delay, and known familial pathogenic variants warrant genetics referral.

Duty to recontact

The practice of informing former patients when a previously reported variant is reclassified or new management guidance emerges; policies vary by institution and jurisdiction.

Pedigree symbols

Square indicates male, circle female, filled affected, half-filled carrier, diagonal line deceased, double line consanguineous mating, and arrow the proband.

Hardy-Weinberg carrier frequency

For an autosomal recessive condition with disease allele frequency q, carrier frequency approximates 2q, often written as 2 times the square root of the incidence.

Hardy-Weinberg equilibrium

Allele and genotype frequencies remain constant across generations in a large randomly mating population without selection, mutation, migration, or genetic drift.

Maternal age aneuploidy risk

Trisomy 21 risk rises with maternal age, from roughly 1 in 1,500 at age 20 to about 1 in 100 at age 40; risk increases for other autosomal trisomies as well.

Screening versus diagnostic testing

Serum screening and cell-free DNA are screening tests with false positives and false negatives; chorionic villus sampling and amniocentesis provide diagnostic karyotype or microarray results.

Cell-free DNA screening

A maternal blood screen analyzing placental DNA fragments; it has high sensitivity for trisomy 21 but is not diagnostic and requires confirmatory invasive testing after a positive result.

Mitochondrial inheritance

Alleles pass through the maternal line only; heteroplasmy causes variable severity among maternal relatives, and affected males do not transmit the variant.

Genomic imprinting

Expression of a gene depends on parent of origin; Prader-Willi and Angelman syndromes arise from distinct parent-of-origin defects in the 15q11-q13 region.

Trisomy 21 cytogenetic forms

About 95% are free trisomy 21, 3-4% Robertsonian translocations (often 14;21), and 1-2% mosaicism; translocation cases warrant parental karyotyping.

Cystic fibrosis carrier frequency

In Northern European ancestry populations, about 1 in 25 are carriers and roughly 1 in 2,500 births are affected, consistent with autosomal recessive inheritance.

Karyotype

A cytogenetic test counting and structurally assessing chromosomes; it detects aneuploidy, large deletions, duplications, inversions, and balanced translocations at low resolution.

Chromosomal microarray

A copy-number assay detecting submicroscopic deletions and duplications; it does not detect balanced rearrangements or most point variants.

FISH

Fluorescence in situ hybridization uses labeled probes to detect specific loci or copy numbers, often on interphase cells or to characterize a known rearrangement.

Next-generation sequencing

Massively parallel sequencing of targeted panels, exomes, or genomes; it detects point variants and small indels but may miss large copy-number changes and repeat expansions.

Trinucleotide repeat expansion

Disorders such as Huntington disease and fragile X syndrome result from unstable repeat expansions; repeat size correlates with age of onset and severity.

Consanguinity

Mating between related individuals, shown by a double line on a pedigree; it increases the chance that offspring inherit two copies of the same recessive allele.

Penetrance

The proportion of individuals carrying a pathogenic variant who show the associated phenotype; reduced penetrance complicates risk estimates in dominant conditions.