ABMGG LGG flashcards

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

Aneuploidy definition

Presence of an abnormal chromosome number that is not an exact multiple of the haploid set, such as trisomy 21 or monosomy X.

Polyploidy definition

A chromosome complement that is a whole-number multiple of the haploid set beyond diploid, such as triploidy (69 chromosomes) or tetraploidy (92 chromosomes).

G-banding resolution limit

Standard metaphase G-banding resolves roughly 400-550 bands per haploid set, so structural changes below about 5-10 Mb may escape detection.

Chromosomal microarray indication

First-tier test for developmental delay, intellectual disability, and multiple congenital anomalies because it detects submicroscopic deletions and duplications.

CMA blind spots

Chromosomal microarray does not detect balanced translocations, inversions, most point mutations, or copy-neutral loss of heterozygosity without SNP probes.

FISH purpose

Fluorescence in situ hybridization uses labeled probes to detect specific loci or chromosome regions, useful for microdeletions, amplifications, and rapid aneuploidy screening.

Karyotype definition

Ordered display of an individual's chromosomes by size, centromere position, and banding pattern, used to detect numerical and large structural abnormalities.

Sanger detection limit

Sanger sequencing generally detects variants at variant allele fractions of about 15-20% or higher, so low-level mosaicism may be missed.

NGS depth and sensitivity

Higher sequencing depth increases the ability to detect low variant allele fractions; germline testing commonly targets about 30x and somatic panels 100x or more.

ACMG variant tiers

Five-tier classification: pathogenic, likely pathogenic, variant of uncertain significance, likely benign, and benign, based on population, computational, and functional evidence.

Variant of uncertain significance

A variant with insufficient or conflicting evidence to classify as pathogenic or benign; it should not be used alone to make a clinical diagnosis.

Mosaicism definition

Presence of two or more genetically distinct cell populations derived from a single zygote, producing variable tissue distribution and often milder phenotypes.

MLPA use case

Multiplex ligation-dependent probe amplification quantifies exon-level copy number, commonly used to detect whole-exon deletions or duplications in single-gene disorders.

PCR contamination control

Including no-template controls and using unidirectional workflow with separate pre- and post-amplification areas reduces false-positive amplification results.

Analytic vs clinical validity

Analytic validity is a test's ability to detect the target accurately; clinical validity is how well the result predicts the associated disease or risk.

Autosomal dominant risk

One affected heterozygous parent confers a 50% recurrence risk per offspring, with possible incomplete penetrance and variable expressivity.

Autosomal recessive risk

Two carrier parents have a 25% chance of an affected child, 50% chance of a carrier child, and 25% chance of an unaffected non-carrier child.

X-linked recessive transmission

Affected males transmit the allele to all daughters, who become carriers, and to no sons; carrier females are usually unaffected.

Mitochondrial inheritance

Alleles are transmitted through the maternal line only; heteroplasmy produces variable severity, and an affected female can pass the variant to all offspring.

Trisomy 21 recurrence

After one affected pregnancy, recurrence risk is about 1% for free trisomy, but higher if a parental Robertsonian translocation is present.

Maternal age effect

Advanced maternal age is the strongest risk factor for fetal autosomal trisomy, reflecting increased meiotic nondisjunction in oocytes.

Newborn screening principle

A population program that identifies presymptomatic infants at risk; a positive result is presumptive and requires confirmatory diagnostic testing.

Prenatal screening vs diagnosis

Screening tests such as maternal serum analytes or cell-free DNA estimate risk; diagnosis requires invasive sampling by chorionic villus sampling or amniocentesis.

Cell-free DNA screening

Analysis of placental DNA in maternal plasma to estimate fetal aneuploidy risk; it is a screening test, not a diagnostic test, and requires confirmation.

Pedigree symbols

Squares denote males, circles females, filled symbols affected individuals, and a diagonal line a deceased individual; consanguinity is shown by a double line.

Penetrance definition

The proportion of individuals carrying a pathogenic variant who express the associated phenotype; incomplete penetrance can hide inheritance patterns.

Expressivity definition

The range of severity or type of clinical features among individuals carrying the same pathogenic variant, explaining variable phenotypes within families.

Consanguinity effect

Mating between related individuals increases the chance that both partners carry the same recessive allele, raising the risk of an affected child.

Carrier screening purpose

Identifies individuals heterozygous for recessive or X-linked conditions so reproductive risk can be quantified and options discussed before or during pregnancy.

Genetic counseling definition

A process of pedigree assessment, risk estimation, and education that supports informed, autonomous reproductive and medical decisions by the patient.

Informed consent elements

Before genetic testing, patients should understand purpose, limitations, possible results, incidental findings, privacy protections, and alternatives.

Predictive testing

Testing an asymptomatic person for a known familial pathogenic variant to estimate future disease risk, requiring pre- and post-test counseling.