CBGC Genetic Counselling Certification (CCGC) cheat sheet

Structured session sequence: contract and agenda setting, history taking, risk communication, decision support, documentation, and follow-up plan.

Pedigree symbols follow standardized nomenclature: squares for males, circles for females, filled symbols for affected individuals, diagonal line for deceased, arrow for proband.

Three-generation pedigree minimum captures consanguinity, ethnic background, and age at diagnosis for relatives, supporting risk stratification.

Risk can be framed as probability (1 in 4), percentage (25%), or natural frequency (25 of 100); natural frequencies improve comprehension in low-numeracy clients.

Teach-back confirms comprehension: ask the client to restate the recurrence risk and next steps in their own words rather than asking 'do you understand?'.

Informed consent elements for testing: purpose, limitations, possible results including variants of uncertain significance, incidental findings, privacy, and cost.

Non-directive counselling presents options with balanced framing; directive language ('you should terminate') breaches the standard of client autonomy.

Documented session notes should record client-stated goals, options discussed, decisions made, and referrals initiated, using objective language.

Autosomal dominant: 50% transmission per pregnancy from an affected heterozygous parent; penetrance and variable expressivity modify observed phenotypes.

Autosomal recessive: 25% affected, 50% carrier, 25% unaffected non-carrier per pregnancy when both parents are carriers.

X-linked recessive: carrier females transmit to 50% of sons (affected) and 50% of daughters (carriers); affected males transmit to no sons and all daughters as carriers.

Bayesian analysis updates carrier risk using prior probability multiplied by conditional probabilities (e.g., negative test sensitivity) and normalized to sum to 1.

Hardy-Weinberg: carrier frequency = 2pq; for rare alleles q is small so 2pq approximates 2q, and q equals the square root of disease incidence.

Mitochondrial inheritance: all offspring of an affected female may be affected with variable severity; offspring of an affected male are unaffected.

Recurrence risk for multifactorial conditions rises with number of affected relatives, earlier age of onset, closer relationship, and more severe phenotype.

Imprinting and uniparental disomy should be considered when phenotype depends on parent of origin or when recessive disease appears with only one carrier parent.

Aneuploidy screening options include first-trimester combined screening, cell-free DNA screening, and second-trimester maternal serum quad screen; each has distinct detection and false-positive rates.

Cell-free DNA screens for trisomies 21, 18, and 13 with high sensitivity but is a screening test; diagnostic confirmation requires chorionic villus sampling or amniocentesis.

Chorionic villus sampling is typically performed at 10-13 weeks and amniocentesis at 15 weeks or later; both carry a small procedure-related miscarriage risk.

Carrier screening panels are offered based on ethnicity and universal panel guidelines; residual risk after a negative test equals prior risk times (1 minus detection rate).

Preimplantation genetic testing requires in vitro fertilization; testing can be for monogenic conditions (PGT-M), structural rearrangements (PGT-SR), or aneuploidy (PGT-A).

Prenatal diagnosis of a fetal anomaly warrants referral for genetic counselling, detailed ultrasound, and discussion of prognosis, management, and pregnancy options.

Expanded carrier screening results must be interpreted with variant classification; variants of uncertain significance in carrier screening should not be assumed pathogenic.

Teratogen exposure counselling addresses critical windows of organogenesis (roughly 3-8 weeks post-conception) and dose-dependent risk.

BRCA1/2 pathogenic variants confer elevated lifetime breast and ovarian cancer risk; risk-reducing salpingo-oophorectomy and mastectomy are established management options.

Lynch syndrome (mismatch repair gene variants) increases colorectal and endometrial cancer risk; tumor screening uses microsatellite instability and immunohistochemistry.

Bethesda-style criteria and clinical prediction models (e.g., family history-based thresholds) identify candidates for hereditary cancer genetic evaluation.

Adenomatous polyposis syndromes include APC-associated familial adenomatous polyposis; attenuated phenotypes present with fewer polyps and later onset.

Somatic tumor testing differs from germline testing; pathogenic somatic findings may prompt germline confirmation when hereditary implication is possible.

Cancer risk estimates combine gene-specific penetrance with family history, lifestyle modifiers, and competing mortality; models differ in the genes and populations they apply to.

Chemoprevention and enhanced surveillance are risk-management options discussed alongside surgical risk reduction, with attention to reproductive plans.

Variant classification for cancer genes follows a five-tier system (pathogenic, likely pathogenic, uncertain significance, likely benign, benign) informing management decisions.

Test tiers: karyotype detects structural and numeric chromosome changes; chromosomal microarray detects copy-number variants; sequencing detects single-nucleotide and small indel changes.

Exome and genome sequencing have lower sensitivity for copy-number variants, repeat expansions, and deep intronic variants than for coding point mutations.

Variant nomenclature follows HGVS standards; classification uses ACMG/AMP five-tier categories with evidence codes for pathogenicity.

Analytical validity, clinical validity, and clinical utility are distinct; a test can be analytically sound yet of uncertain clinical utility.

Turnaround time, tissue type, and test limitations should be documented in the report and communicated to the client before testing.

Incidental and secondary findings policies should be discussed pre-test; opt-out is available for secondary findings in clinical genomic sequencing.

Confirmation testing (e.g., Sanger sequencing) is used to verify reportable variants, especially in research or prenatal contexts.

Quality metrics include coverage depth, allele balance, and positive predictive value, which depends on pretest probability and assay specificity.

Core ethical principles: autonomy, beneficence, non-maleficence, and justice guide counselling decisions and conflict resolution.

Genetic Information Nondiscrimination Act (US) prohibits health insurance and employment discrimination based on genetic information but does not cover life, disability, or long-term care insurance.

Informed consent for genetic testing must address privacy risks, data storage, family implications, and the possibility of uncertain results.

Duty to warn versus confidentiality: disclosure of genetic risk to relatives generally requires client permission, with limited legal exceptions varying by jurisdiction.

Psychosocial assessment screens for anxiety, depression, guilt, family conflict, and decisional conflict; validated tools and referral to mental health services support care.

Adolescent and pediatric testing is generally deferred for adult-onset conditions unless clinical benefit exists during childhood.

Cultural humility and interpreter services are required for equitable care; family dynamics and stigma may affect disclosure of results.

Insurance and legal protections vary internationally; counsellors should verify jurisdiction-specific law rather than assume US protections apply.

Evidence hierarchy: systematic reviews and randomized trials rank above cohort studies, case series, and expert opinion for questions of intervention effect.

Sensitivity is true positives divided by all affected; specificity is true negatives divided by all unaffected; positive predictive value depends on prevalence.

Likelihood ratios convert pretest odds to posttest odds; a likelihood ratio of 1 does not change probability.

Relative risk and odds ratios describe association magnitude but do not alone establish causation; confidence intervals indicate estimate precision.

Systematic review appraisal considers search strategy, risk of bias, heterogeneity, and publication bias.

Guideline development uses grading systems (e.g., evidence quality and strength of recommendation) that should be distinguished from the evidence itself.

Scope of practice, supervision requirements, and continuing education obligations are set by the certifying body and provincial or state regulators.

Documentation and billing standards, conflict-of-interest disclosure, and research ethics approval are part of professional accountability.

Management plans link genetic diagnosis to surveillance intervals, risk-reducing interventions, and specialist referrals with defined timelines.

Referral triggers include confirmed pathogenic variants, uncertain results requiring specialist interpretation, and psychosocial needs beyond counselling scope.

Pharmacogenomic results inform drug selection and dosing; clinical decision support and guidelines should guide interpretation before acting.

Enzyme replacement and substrate reduction therapies exist for selected lysosomal storage disorders; early diagnosis can improve outcomes.

Newborn screening follow-up requires confirmatory testing and coordination with metabolic specialists; false positives are expected and must be communicated carefully.

Reproductive options after a diagnosis include prenatal diagnosis, preimplantation genetic testing, gamete donation, and acceptance of risk, each with distinct implications.

Care coordination includes sharing results with the primary care provider and specialists, with client consent, and documenting the communication.

Outcome monitoring and re-referral criteria should be specified so that changing variant classifications or new evidence can prompt plan revision.