ABGC Certification Examination (CGC credential) cheat sheet

Genetic Counseling Practice

• Informed consent for genetic testing requires disclosure of test purpose, limitations (variant of uncertain significance, incidental findings), storage and secondary use of samples, and policies on disclosure to relatives.

• Pedigree symbols: filled = affected, half-filled = carrier, arrow = proband, diagonal line = deceased, double line = consanguineous mating, square = male, circle = female, diamond = sex unknown or pregnancy.

• Autosomal dominant: vertical transmission, male-to-male transmission possible, 50% recurrence per child of an affected heterozygote, and reduced penetrance can skip generations.

• Autosomal recessive: horizontal pattern, 25% recurrence for two carriers, consanguinity raises risk; carrier frequency relates to disease incidence by 2√(q) under Hardy-Weinberg.

• X-linked recessive: males affected, no male-to-male transmission, all daughters of an affected male are carriers; carrier females may show skewed X-inactivation phenotypes.

• Bayesian risk calculation: posterior odds = prior odds × likelihood ratio; unaffected offspring and negative test results multiply the unaffected (or false-negative) probability into the denominator.

• Mitochondrial inheritance: transmitted by mothers to all children, males do not transmit; heteroplasmy produces variable severity and threshold effects.

• Trisomy risk rises with maternal age; recurrence risk for an isolated trisomy is about 1% or the age-related risk, whichever is higher, absent a parental translocation.

• Grief and adaptation follow non-linear stages; counselor responses include normalizing reactions, exploring coping, and screening for depression or anxiety requiring referral.