Mixed Deck — All CGC Topics Flashcards

Which concept best explains the variable severity of mitochondrial disease among maternally related family members?

Answer: Heteroplasmy

Heteroplasmy is the mix of mutant and normal mtDNA, and the proportion varies between cells and individuals, producing variable severity.

A pedigree shows an affected father who has no affected sons but all affected daughters. Which inheritance pattern is most likely?

Answer: X-linked dominant

Fathers pass their only X to all daughters and none to sons, so absent male-to-male transmission with all daughters affected indicates X-linked dominant inheritance.

Which of the following describes a mutation?

Answer: A change in the DNA sequence

A mutation is defined as a change in the DNA sequence of an organism. These changes can range from a single nucleotide alteration to large-scale chromosomal rearrangements. Mutations can occur spontaneously or be induced by external factors, and they are the ultimate source of genetic variation, sometimes leading to disease or providing evolutionary advantage.

A patient asks about the difference between a 'screen positive' and a 'diagnostic positive' result for Down syndrome. The counselor correctly explains that:

Answer: A screen positive indicates increased risk but requires diagnostic confirmation; a diagnostic positive confirms the diagnosis

Screening identifies individuals at increased risk who need diagnostic testing, while diagnostic testing provides definitive chromosomal confirmation.

Which condition is typically associated with autosomal recessive inheritance?

Answer: Cystic fibrosis

Cystic fibrosis is a classic example of an autosomal recessive condition.

Which law protects individuals from genetic discrimination in the U.S.?

Answer: GINA

The Genetic Information Nondiscrimination Act (GINA) prohibits misuse of genetic information.

What does autosomal dominant inheritance imply?

Answer: One copy of a mutated gene can cause the condition.

A single copy of the mutated gene from either parent can cause the disorder.

Which of the following epigenetic modifications most directly contributes to gene silencing by adding a chemical group to cytosine residues in CpG islands?

Answer: DNA methylation

DNA methylation at CpG islands, catalyzed by DNA methyltransferases, is strongly associated with transcriptional silencing of the associated gene.

What term describes the phenomenon where the expression of a gene depends on whether it was inherited from the mother or the father?

Answer: Genomic imprinting

Genomic imprinting is an epigenetic process by which gene expression is determined by the parental origin of the allele.

Preimplantation genetic testing for monogenic conditions (PGT-M) requires which INITIAL step?

Answer: Identifying the specific familial pathogenic variant through proband testing

PGT-M requires knowledge of the exact familial variant so the laboratory can design a specific probe or analysis strategy for the embryo.

Which communication technique is most effective when disclosing a pathogenic variant result to a patient?

Answer: Deliver information in small chunks with pauses to check understanding

Chunking information and checking understanding allows patients to process difficult news more effectively.

Which lifetime breast cancer risk estimate generally triggers consideration of annual breast MRI screening in addition to mammography?

Answer: 20% or greater

ACS and NCCN guidelines recommend supplemental MRI when model-estimated lifetime risk is 20% or higher.

Which role does a genetic counselor play in test interpretation?

Answer: Interpret results for patients

Genetic counselors are healthcare professionals with specialized education and training in medical genetics and counseling. Their primary role is to interpret complex genetic test results for patients, explaining what the results mean for their health and their family. They also provide risk assessment, education, and support, helping patients make informed decisions about genetic testing and its implications.

Multiple endocrine neoplasia type 2 (MEN2) is caused by germline pathogenic variants in which gene?

Answer: RET

MEN2 is caused by activating germline variants in the RET proto-oncogene and is associated with medullary thyroid cancer, pheochromocytoma, and hyperparathyroidism.

Which of the following best describes a de novo mutation?

Answer: A mutation that arises newly in the affected individual and is not present in either parent

A de novo mutation arises spontaneously in the proband and is not inherited from either parent, often explaining isolated cases of dominant disorders.

In the context of genetic counseling, 'nondirectiveness' primarily means the counselor should:

Answer: Support client autonomy without imposing the counselor's values

Nondirectiveness means supporting patient autonomy and self-determination rather than directing patients toward specific choices.

What is the first step in genetic risk assessment?

Answer: Collect detailed family history.

Collecting a comprehensive family history helps identify patterns of inherited conditions.

Which of the following BEST describes the purpose of a pedigree in a genetic counseling session?

Answer: To visually map family medical history and identify inheritance patterns

Pedigrees systematically capture multigenerational family history to analyze inheritance patterns and identify at-risk relatives.

When counseling a couple for whom one partner is a carrier of an X-linked recessive condition, which reproductive outcome is CORRECT?

Answer: 50% of sons will be affected and 50% of daughters will be carriers

For X-linked recessive conditions, carrier mothers pass the variant to 50% of sons (who are affected) and 50% of daughters (who are carriers).

In a population where the frequency of a recessive allele (q) is 0.1, the expected carrier frequency under Hardy-Weinberg equilibrium is:

Answer: 0.18 (18%)

Carrier frequency = 2pq = 2 × 0.9 × 0.1 = 0.18, meaning 18% of the population are heterozygous carriers.