Genetic counseling principles US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Genetic counseling principles. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Genetic counseling principles US Medical PG Question 1: A 25-year-old man with a genetic disorder presents for genetic counseling because he is concerned about the risk that any children he has will have the same disease as himself. Specifically, since childhood he has had difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy. He has also had diarrhea and malabsorption requiring enzyme replacement therapy. If his wife comes from a population where 1 in 10,000 people are affected by this same disorder, which of the following best represents the likelihood a child would be affected as well?
- A. 0.01%
- B. 2%
- C. 0.5%
- D. 1% (Correct Answer)
- E. 50%
Genetic counseling principles Explanation: ***Correct Option: 1%***
- The patient's symptoms (difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy; diarrhea and malabsorption requiring enzyme replacement therapy) are classic for **cystic fibrosis (CF)**, an **autosomal recessive disorder**.
- For an autosomal recessive disorder with a prevalence of 1 in 10,000 in the general population, **q² = 1/10,000**, so **q = 1/100 = 0.01**. The carrier frequency **(2pq)** is approximately **2q = 2 × (1/100) = 1/50 = 0.02**.
- The affected man is **homozygous recessive (aa)** and will always pass on the recessive allele. His wife has a **1/50 chance of being a carrier (Aa)**. If she is a carrier, she has a **1/2 chance of passing on the recessive allele**.
- Therefore, the probability of an affected child = **(Probability wife is a carrier) × (Probability wife passes recessive allele) = 1/50 × 1/2 = 1/100 = 1%**.
*Incorrect Option: 0.01%*
- This percentage is too low and does not correctly account for the carrier frequency in the population and the probability of transmission from a carrier mother.
*Incorrect Option: 2%*
- This represents approximately the carrier frequency (1/50 ≈ 2%), but does not account for the additional 1/2 probability that a carrier mother would pass on the recessive allele.
*Incorrect Option: 0.5%*
- This value would be correct if the carrier frequency were 1/100 instead of 1/50, which does not match the given population prevalence.
*Incorrect Option: 50%*
- **50%** would be the risk if both parents were carriers of an autosomal recessive disorder (1/4 chance = 25% for affected, but if we know one parent passes the allele, conditional probability changes). More accurately, 50% would apply if the disorder were **autosomal dominant** with one affected parent, which is not the case here.
Genetic counseling principles US Medical PG Question 2: A healthy 30-year-old woman comes to the physician with her husband for preconception counseling. Her husband is healthy but she is concerned because her brother was recently diagnosed with a genetic liver condition for which he takes penicillamine. Her father-in-law has liver cirrhosis and a tremor. The results of genetic testing show that both the patient and her husband are carriers of a mutation in the ATP7B gene. Which of the following is the chance that this patient’s offspring will eventually develop the hereditary condition?
- A. 0%
- B. 25% (Correct Answer)
- C. 100%
- D. 50%
- E. 75%
Genetic counseling principles Explanation: ***25%***
- The familial history (brother with a genetic liver condition, father-in-law with cirrhosis and tremor) and the **ATP7B gene mutation** indicate **Wilson's disease**, which is typically inherited in an **autosomal recessive** pattern.
- If both parents are carriers (heterozygous for the mutation), the probability that their offspring will inherit two copies of the mutated gene (one from each parent) and, therefore, develop the condition is **25%** as per Mendelian inheritance.
*0%*
- This is incorrect because both parents are identified as carriers, meaning there is a definite risk of passing on the mutated genes to their offspring.
- For the risk to be 0%, at least one parent would need to be completely free of the mutation or the inheritance pattern would need to be dominant with no penetrance.
*100%*
- This would only be the case if both parents had the disease (were homozygous for the mutation) or if the condition were dominant and at least one parent had the disease and passed on the dominant allele.
- Since both are carriers, the chance of inheriting two mutated alleles is not 100%.
*50%*
- A 50% chance would apply if one parent had the disease (homozygous recessive) and the other was a carrier, or if it were an autosomal dominant condition with one affected heterozygous parent.
- This does not reflect the inheritance pattern for two carrier parents in an autosomal recessive condition.
*75%*
- A 75% chance is not typical for a single genetic outcome in standard Mendelian inheritance patterns from carrier parents.
- In the context of two carriers for an autosomal recessive trait, 75% represents the chance of the offspring either being a carrier (50%) or being completely unaffected (25%), but not the chance of developing the condition.
Genetic counseling principles US Medical PG Question 3: A 28-year-old woman dies shortly after receiving a blood transfusion. Autopsy reveals widespread intravascular hemolysis and acute renal failure. Investigation reveals that she received type A blood, but her medical record indicates she was type O. In a malpractice lawsuit, which of the following elements must be proven?
- A. Duty, breach, causation, and damages (Correct Answer)
- B. Only duty and breach
- C. Only breach and causation
- D. Duty, breach, and damages
Genetic counseling principles Explanation: ***Duty, breach, causation, and damages***
- In a medical malpractice lawsuit, all four elements—**duty, breach, causation, and damages**—must be proven for a successful claim.
- The healthcare provider had a **duty** to provide competent care, they **breached** that duty by administering the wrong blood type, this breach **caused** the patient's death and renal failure, and these injuries constitute **damages**.
*Only duty and breach*
- While **duty** and **breach** are necessary components, proving only these two is insufficient for a malpractice claim.
- It must also be demonstrated that the breach directly led to the patient's harm and resulted in legally recognized damages.
*Only breach and causation*
- This option omits the crucial elements of professional **duty** owed to the patient and the resulting **damages**.
- A claim cannot succeed without establishing that a duty existed and that quantifiable harm occurred.
*Duty, breach, and damages*
- This option misses the critical element of **causation**, which links the provider's breach of duty to the patient's injuries.
- Without proving that the breach *caused* the damages, even if a duty was owed and breached, and damages occurred, the claim would fail.
Genetic counseling principles US Medical PG Question 4: An 87-year-old man with glioblastoma multiforme is informed that the size and location of the tumor make operative resection impossible, and he has a prognosis of between 3-6 months. The patient then asks whether it would be possible to get a prescription for lethal medications so that he would be able to end his life if his situation deteriorated further. The physician says that he is unable to prescribe such drugs because assisted suicide is not legal in their state. Refusing to help a patient commit suicide is most consistent with which of the following ethical principles?
- A. Beneficence
- B. Distributive justice
- C. Non-maleficence (Correct Answer)
- D. Autonomy
- E. Formal justice
Genetic counseling principles Explanation: ***Non-maleficence***
- Non-maleficence is the ethical principle to **"do no harm"** to the patient, one of the four core pillars of medical ethics.
- In the context of physician-assisted suicide, refusing to prescribe lethal medications is **most directly grounded** in the principle of not causing harm or death to the patient, even when requested.
- While legal constraints exist, the **underlying ethical rationale** for opposition to physician-assisted suicide in traditional medical ethics is that actively ending a patient's life violates the fundamental duty not to harm.
- This principle holds that the physician's role is to **preserve life and relieve suffering** through palliative care, not to cause death.
*Formal justice*
- Formal justice refers to the principle of treating **similar cases in a similar manner** and applying rules consistently.
- While the physician is following the law equally for all patients, formal justice is more about **procedural fairness** than the substantive ethical principle underlying the refusal to end life.
- This principle is relevant but is **not the primary ethical foundation** for opposing physician-assisted suicide.
*Beneficence*
- Beneficence is the ethical principle of acting in the **best interest of the patient** and promoting their well-being.
- While some might argue that respecting the patient's wish could be beneficent, traditional medical ethics views **preserving life** and providing comfort care as beneficent, rather than facilitating death.
- This principle could be invoked on either side of the debate but is **less specific** than non-maleficence in this context.
*Autonomy*
- Autonomy is the principle of respecting a patient's right to make **decisions about their own medical care**.
- While the patient is expressing an autonomous wish, the physician's refusal demonstrates that autonomy has **limits when it conflicts** with other ethical principles (non-maleficence) and legal constraints.
- This scenario represents a tension between autonomy and other ethical duties.
*Distributive justice*
- Distributive justice concerns the **fair allocation of resources** and burdens within society.
- This principle is generally applied to situations involving healthcare access, resource scarcity, or equitable treatment for groups of people, and is **not directly relevant** to an individual physician's decision regarding assisted suicide.
Genetic counseling principles US Medical PG Question 5: A 35-year-old woman gravida 2, para 1, comes to the physician for her first prenatal visit. Pregnancy and delivery of her first child were uncomplicated. She is not sure about the date of her last menstrual period. Pelvic examination shows a uterus consistent in size with a 10-week gestation. An ultrasound examination confirms the gestational age and shows one fetus with no indication of multiple gestations. During counseling on pregnancy risks and possible screening and diagnostic tests, the patient states she would like to undergo screening for Down syndrome. She would prefer immediate and secure screening with a low risk to herself and the fetus. Which of the following is the most appropriate next step in management at this time?
- A. Nuchal translucency, pregnancy-associated plasma protein-A, human chorionic gonadotropin
- B. Maternal serum α-fetoprotein, human chorionic gonadotropin, unconjugated estriol, and inhibin A
- C. Chorionic villus sampling
- D. Amniocentesis
- E. Cell-free fetal DNA testing (Correct Answer)
Genetic counseling principles Explanation: ***Cell-free fetal DNA testing***
- This is the most appropriate choice given the patient's desire for **immediate and secure screening with low risk** because it is a **non-invasive prenatal screening (NIPS)** method offering high sensitivity and specificity for Down syndrome, particularly in higher-risk pregnancies.
- It involves a simple maternal blood draw and can be performed as early as **10 weeks of gestation**, perfectly aligning with the patient's current gestational age and desire for early screening.
*Nuchal translucency, pregnancy-associated plasma protein-A, human chorionic gonadotropin*
- This combination represents the **first-trimester combined screen**, which is typically performed between 11 and 14 weeks of gestation. While suitable for early screening, **cell-free DNA testing offers higher detection rates and lower false-positive rates** for Down syndrome.
- The patient specifically asked for the most **secure and least risky** screening, and NIPS outperforms the combined screen in terms of diagnostic accuracy for aneuploidies.
*Maternal serum α-fetoprotein, human chorionic gonadotropin, unconjugated estriol, and inhibin A*
- This refers to the **quad screen**, which is typically performed in the **second trimester (15-20 weeks)**, making it too late for the patient's desire for immediate screening at 10 weeks gestational age.
- While a widely used screening tool, the quad screen has a **lower detection rate** for Down syndrome compared to cell-free DNA testing.
*Chorionic villus sampling*
- **Chorionic villus sampling (CVS)** is a **diagnostic, invasive procedure** that carries a small risk of miscarriage (approximately 1 in 455 or 0.22%) and is not a screening test.
- Although it can be performed earlier (typically between 10 and 13 weeks), the patient specifically requested a **low-risk screening** option, which CVS is not.
*Amniocentesis*
- **Amniocentesis** is also an **invasive diagnostic procedure** with a risk of miscarriage (approximately 1 in 900 or 0.11%) and is typically performed in the **second trimester (15-20 weeks)**.
- This option is unsuitable because the patient is at 10 weeks gestation and desires **immediate and low-risk screening**, not a diagnostic procedure with procedural risks a few weeks later.
Genetic counseling principles US Medical PG Question 6: A 31-year-old man and his wife were referred to a genetic counselor. They are concerned about the chance that their children are likely to inherit certain conditions that run in their families. The wife's father and grandfather are both healthy, but her grandfather cannot see the color red. The husband is unaware if any member of his family has the same condition. The geneticist provides some details about genetic diseases and inheritance patterns, then orders lab tests to analyze the gene mutations carried by both partners. Which of the following are the correct terms regarding the genotype and phenotype of males affected by the condition described?
- A. Homozygote; reduced or incomplete penetrance
- B. Heterozygotes; reduced or incomplete penetrance
- C. Hemizygous; reduced or incomplete penetrance
- D. Heterozygotes; full penetrance
- E. Hemizygous; full penetrance (Correct Answer)
Genetic counseling principles Explanation: ***Hemizygous; full penetrance***
- The condition described (**red color blindness**) is an **X-linked recessive** trait, meaning males have only one X chromosome and are thus **hemizygous** for genes on the X chromosome.
- **Full penetrance** in X-linked recessive traits means that if a male inherits the affected X chromosome, he will express the phenotype of the condition.
*Homozygote; reduced or incomplete penetrance*
- **Homozygous** refers to having two identical alleles for a particular gene, which is not applicable to an X-linked gene in males as they only have one X chromosome.
- **Reduced or incomplete penetrance** means that a person with the genotype may or may not express the phenotype, which is typically not the case for males with X-linked recessive color blindness.
*Heterozygotes; reduced or incomplete penetrance*
- **Heterozygous** means having two different alleles for a gene; this term is not applicable to males regarding X-linked genes.
- Males are **hemizygous** for X-linked genes, meaning they only have one allele, not two different ones.
*Hemizygous; reduced or incomplete penetrance*
- While males are indeed **hemizygous** for X-linked genes like color blindness, the penetrance for red-green color blindness in males is generally considered to be **full**, meaning if they carry the mutated gene, they will express the trait.
- **Reduced penetrance** would imply that some males with the genotype might not exhibit color blindness, which is rare for this condition.
*Heterozygotes; full penetrance*
- The term **heterozygous** applies to individuals with two different alleles for a gene, which is not the genetic state of males for X-linked genes.
- While penetrance is full, the term **heterozygotes** is incorrect for defining the male genotype in this context.
Genetic counseling principles US Medical PG Question 7: A 16-year-old boy is brought to his primary care physician for evaluation of visual loss and is found to have lens subluxation. In addition, he is found to have mild scoliosis that is currently being monitored. Physical exam reveals a tall and thin boy with long extremities. Notably, his fingers and toes are extended and his thumb and little finger can easily encircle his wrist. On this visit, the boy asks his physician about a friend who has a very similar physical appearance because his friend was recently diagnosed with a pheochromocytoma. He is worried that he will also get a tumor but is reassured that he is not at increased risk for any endocrine tumors. Which of the following genetic principles most likely explains why this patient and his friend have a similar physical appearance and yet only one is at increased risk of tumors?
- A. Variable expression
- B. Locus heterogeneity (Correct Answer)
- C. Anticipation
- D. Incomplete penetrance
- E. Pleiotropy
Genetic counseling principles Explanation: ***Locus heterogeneity***
- This principle explains that **similar phenotypes** (like the Marfanoid habitus) can result from mutations at **different genetic loci**. In this case, two distinct genetic conditions (Marfan syndrome and MEN 2B for the friend) can both cause tall stature and long limbs, but only one is associated with pheochromocytoma.
- The patient's presentation of **lens subluxation**, **scoliosis**, and **Marfanoid habitus** strongly suggests Marfan syndrome, typically caused by *FBN1* mutations, which does not predispose to pheochromocytomas. The friend's similar appearance coupled with pheochromocytoma suggests a different genetic condition, such as **Multiple Endocrine Neoplasia Type 2B (MEN 2B)**, which involves *RET* gene mutations.
*Variable expression*
- This describes the phenomenon where individuals with the **same genotype** exhibit **different degrees of severity** in their phenotype. It doesn't explain why two individuals with similar physical features have different underlying genetic causes and therefore different risks for specific complications like tumors.
- Variable expression would suggest that if both individuals had the same genetic mutation, they might show different levels of Marfanoid features or tumor development, but it wouldn't account for the complete absence of tumor risk in one.
*Anticipation*
- This refers to a genetic phenomenon where the **severity of a genetic disease increases** and/or the **age of onset decreases** in successive generations.
- Anticipation is typically seen in disorders caused by **trinucleotide repeat expansions** (e.g., Huntington's disease, myotonic dystrophy) and is not relevant to explaining different tumor risks with similar phenotypes across unrelated individuals.
*Incomplete penetrance*
- This occurs when individuals with a specific genotype **do not always express the associated phenotype**, meaning some individuals with the disease-causing mutation show no symptoms.
- Incomplete penetrance does not explain why two individuals with similar physical features have different genetic conditions leading to varied tumor risks; it focuses on whether a known mutation will manifest at all, not on different genetic causes for similar traits.
*Pleiotropy*
- This is when a **single gene mutation affects multiple seemingly unrelated phenotypic traits**. Marfan syndrome itself is an example of pleiotropy, as a mutation in *FBN1* affects the skeletal, ocular, and cardiovascular systems.
- While both conditions (Marfan syndrome and MEN 2B) exhibit pleiotropy, this principle doesn't explain why two different genetic conditions would cause similar Marfanoid features but distinct tumor risks. It describes the multiple effects of *one* mutation, not the possibility of *different* mutations leading to similar effects.
Genetic counseling principles US Medical PG Question 8: An investigator studying viral mutation isolates a virus strain from the gastric contents of an infant with gastroenteritis. This virus has a nonenveloped RNA genome with 11 segments and an icosahedral symmetrical capsid. The investigator finds that if 2 strains of this virus coinfect a single host cell, some of the resulting viral progeny have genome segments derived from both parental viruses. The observed phenomenon is most likely also seen in which of the following viral families?
- A. Caliciviruses
- B. Orthomyxoviruses (Correct Answer)
- C. Flaviviruses
- D. Retroviruses
- E. Picornaviruses
Genetic counseling principles Explanation: ***Orthomyxoviruses***
- The description of a virus with a **segmented RNA genome** undergoing reassortment (mixing segments from coinfecting strains) is characteristic of **Orthomyxoviruses**, which notably include the influenza virus.
- Influenza virus is well-known for its ability to **reassort** its **8 segmented RNA genome**, leading to antigenic shifts responsible for pandemics.
*Caliciviruses*
- **Caliciviruses** (e.g., Norovirus) have a **single-stranded, non-segmented RNA genome** and do not undergo genomic reassortment.
- They are a common cause of **gastroenteritis** but their genetic features differ.
*Flaviviruses*
- **Flaviviruses** (e.g., Dengue, Yellow Fever, Zika) possess a **single-stranded, non-segmented RNA genome**.
- They replicate via a polyprotein cleavage mechanism and do not exhibit genomic reassortment.
*Retroviruses*
- **Retroviruses** (e.g., HIV) have a **diploid, positive-sense, single-stranded RNA genome** that is reverse transcribed into DNA.
- While they can undergo **recombination** during reverse transcription, this is distinct from the described reassortment of segmented genomes.
*Picornaviruses*
- **Picornaviruses** (e.g., Poliovirus, Rhinovirus) have a **single-stranded, non-segmented RNA genome**.
- They are known for their rapid replication but do not exhibit genomic segmentation or reassortment.
Genetic counseling principles US Medical PG Question 9: A homeless 45-year-old man presents to the emergency room in December complaining of malaise, body aches, chills, and fever. He reports that his symptoms started 4 days ago. His myalgias and chills have begun to resolve, but now he is starting to develop a dry cough, dyspnea, and a sore throat. He does not have a primary care provider and has not had any vaccinations in over 2 decades. He receives medical care from the emergency room whenever he is feeling ill. His temperature is 103°F (39.4°C), blood pressure is 130/70 mmHg, pulse is 115/min, and respirations are 22/min. On exam, he appears fatigued with mildly increased work of breathing. A chest radiograph is negative. A nasopharyngeal viral culture is positive for an orthomyxovirus. Upon further review of the patient’s medical record, he was diagnosed with the same condition 1 year ago in November. Which of the following mechanisms is responsible for pandemics of this patient’s disease?
- A. Reassortment (Correct Answer)
- B. Complementation
- C. Transduction
- D. Phenotypic mixing
- E. Recombination
Genetic counseling principles Explanation: ***Reassortment***
- This patient presents with **influenza**, confirmed by a positive nasopharyngeal viral culture for an **orthomyxovirus**. The seasonal nature of his illness, despite having it before, points to antigenic changes.
- **Reassortment** (also known as **antigenic shift**) is the primary mechanism responsible for **influenza pandemics**. It involves the exchange of entire gene segments between different influenza strains (e.g., human and avian or swine strains) when a host cell is co-infected with two distinct viral strains, leading to a new subtype with novel hemagglutinin (HA) or neuraminidase (NA) proteins that human populations have little to no immunity against.
*Complementation*
- **Complementation** occurs when two viruses infect the same cell, and one virus provides a **necessary gene product** that the other mutated or defective virus lacks, allowing the latter to replicate.
- This mechanism does not involve genetic exchange leading to new viral subtypes and is therefore not responsible for the emergence of pandemic strains.
*Transduction*
- **Transduction** is a process by which **bacteriophages** (viruses that infect bacteria) transfer bacterial DNA from one bacterium to another.
- This is a mechanism of gene transfer in bacteria and is not relevant to the genetic changes in influenza viruses.
*Phenotypic mixing*
- **Phenotypic mixing** occurs when the genome of one virus is packaged into the **capsid** of another virus, or when genetic material from two viruses is packaged into a mixed capsid.
- While it can alter the tropism or antigenicity of progeny viruses temporarily, it does not involve a change in the viral genome itself and is therefore not responsible for permanent shifts leading to pandemics.
*Recombination*
- **Recombination** involves the exchange of genetic material between two homologous DNA or RNA molecules, leading to new combinations of genes within the same gene segment.
- While recombination can occur in viruses, **reassortment** of entire gene segments (antigenic shift) is the specific and most significant mechanism for creating novel influenza strains capable of causing pandemics, rather than recombination within gene segments.
Genetic counseling principles US Medical PG Question 10: An investigator is studying the function of the endoplasmic reticulum in genetically modified lymphocytes. A gene is removed that facilitates the binding of ribosomes to the endoplasmic reticulum. Which of the following processes is most likely to be impaired as a result of this genetic modification?
- A. Production of secretory proteins (Correct Answer)
- B. Neutralization of toxins
- C. Ubiquitination of proteins
- D. α-Oxidation of fatty acids
- E. Synthesis of ketone bodies
Genetic counseling principles Explanation: ***Production of secretory proteins***
- Ribosomes bound to the **rough endoplasmic reticulum (RER)** are responsible for synthesizing proteins destined for secretion, insertion into membranes, or delivery to organelles like lysosomes.
- If ribosomes cannot bind to the ER, these proteins will be synthesized in the **cytosol** and lack the proper signals and processing for their intended destination and function.
*Neutralization of toxins*
- The **smooth endoplasmic reticulum (SER)**, not the RER, is primarily involved in **detoxification** processes, particularly drug metabolism and neutralization of toxins.
- This function relies on enzymes embedded within the SER membrane and is largely independent of ribosome binding.
*Ubiquitination of proteins*
- **Ubiquitination** is a post-translational modification that tags proteins for degradation by the **proteasome** or for trafficking to specific cellular compartments.
- This process occurs primarily in the **cytosol** and does not directly rely on ribosome binding to the ER for protein synthesis.
*α-Oxidation of fatty acids*
- **α-oxidation of fatty acids** is a metabolic pathway that occurs primarily in the **peroxisomes**.
- It is distinct from protein synthesis on the ER and would not be directly impacted by the inability of ribosomes to bind to the ER.
*Synthesis of ketone bodies*
- The **synthesis of ketone bodies** (ketogenesis) primarily occurs in the **mitochondria** of liver cells.
- This metabolic pathway is not directly dependent on ribosome binding to the endoplasmic reticulum for its function.
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