Newborn Screening for Genetic Disorders — MCQs
All are provisions of WHO mental health Gap Action Programme (mhGAP), except:
All of the following statements are true regarding non-invasive prenatal screening (NIPT) test except:
Which of the following is an example of prospective screening?
Disputed maternity can be solved by using the following tests, EXCEPT:
Phenylketonuria is due to a deficiency of:
To assess thyroid profile of a newborn, which of the following is mandatory?
34 week primigravida punjabi khatri comes with history of consanguineous marriage, with history of repeated blood transfusion to her sibling since 8 months of age. The first diagnostic test is -
18 weeks pregnant female presents with no high risk of NTD and low risk of trisomy 21 on quad test. What is the most appropriate next step in management?
Which of the following statements regarding phenylketonuria (PKU) is false?
Increasing severity of intellectual disability of male members over generations is a result of ?
Newborn Screening for Genetic Disorders Indian Medical PG Practice Questions and MCQs
Question 1: All are provisions of WHO mental health Gap Action Programme (mhGAP), except:
- A. Communication regarding care
- B. Human rights
- C. Screening family members (Correct Answer)
- D. Social support
Explanation: ***Screening family members*** - The **WHO mhGAP** primarily focuses on scaling up care for **priority mental, neurological, and substance use disorders** in low- and middle-income countries. It does not explicitly include the provision of routine screening of family members of affected individuals. - While family support is crucial, direct screening of asymptomatic family members for psychiatric disorders is not a core component of the program's defined interventions for service delivery. *Communication regarding care* - **Effective communication** is a fundamental aspect of the **WHO mhGAP** to ensure patients and their families understand their condition and treatment plan. - It emphasizes **patient-centered care** and informed decision-making, which rely heavily on clear and empathetic communication from healthcare providers. *Human rights* - **Human rights** are a foundational principle of the **WHO mhGAP**, ensuring that individuals with mental disorders receive care without discrimination and with respect for their dignity and autonomy. - The program advocates for policies and practices that protect the rights of people with mental health conditions. [1] *Social support* - **Social support** is a crucial component promoted by the **WHO mhGAP**, recognizing its role in recovery and well-being for individuals with mental health conditions. - The program encourages interventions that strengthen social ties and community integration to reduce isolation and improve outcomes.
Question 2: All of the following statements are true regarding non-invasive prenatal screening (NIPT) test except:
- A. High negative predictive value
- B. Positive test needs further confirmation
- C. Used in screening for aneuploidies
- D. Evaluates fetal blood taken by cordocentesis for fetal abnormalities (Correct Answer)
Explanation: ***Evaluates fetal blood taken by cordocentesis for fetal abnormalities*** - NIPT evaluates **cell-free fetal DNA** from a maternal blood sample, not fetal blood obtained via cordocentesis. - **Cordocentesis** is an invasive diagnostic procedure used to obtain fetal blood, typically for rapid karyotyping or hematologic studies, and is not part of NIPT. *Positive test needs further confirmation* - NIPT is a **screening test**, and a positive result indicates an increased risk, not a definitive diagnosis. - Any positive NIPT result requires **confirmatory diagnostic testing**, such as amniocentesis or chorionic villus sampling (CVS), due to the possibility of false positives. *High negative predictive value* - NIPT has a **very high negative predictive value (NPV)**, meaning that a negative result reliably indicates a very low likelihood of the screened aneuploidies being present. - This high NPV makes NIPT an effective tool for **reassuring patients** with negative results and reducing the need for invasive diagnostic procedures. *Used in screening for aneuploidies* - NIPT is primarily used to screen for common **fetal aneuploidies**, such as **Trisomy 21 (Down syndrome)**, Trisomy 18 (Edwards syndrome), and Trisomy 13 (Patau syndrome). - It analyzes fragments of fetal DNA circulating in the maternal bloodstream to detect chromosomal dosage imbalances.
Question 3: Which of the following is an example of prospective screening?
- A. Immigrant screening
- B. Neonate for thyroid diseases (Correct Answer)
- C. Pap smear for 45-year female
- D. Diabetes mellitus for 40-year male
Explanation: ***Neonate for thyroid diseases*** - **Prospective/Mass screening** involves screening an **entire population or specific subgroup** before symptoms appear for early detection and intervention - **Neonatal screening for congenital hypothyroidism** is performed universally on all newborns to identify and treat the condition early, preventing severe developmental disabilities and intellectual impairment - This represents **true population-wide screening** applied systematically to every member of the birth cohort *Immigrant screening* - This is **selective screening** targeting a specific high-risk group rather than universal population screening - Primary goal is to **control disease transmission** and identify conditions posing public health risks upon entry - Not applied to the general population systematically *Pap smear for 45-year female* - This is an example of **organized screening** for cervical cancer in a specific age group - While valuable for secondary prevention, it targets women within defined age ranges (typically 21-65 years) - Not universal across all age groups like neonatal screening *Diabetes mellitus for 40-year male* - This represents **opportunistic or selective screening** based on age and risk factors - Not a universal population-wide program applied systematically to everyone - Typically done as part of routine health checks for at-risk individuals
Question 4: Disputed maternity can be solved by using the following tests, EXCEPT:
- A. Blood grouping
- B. HLA typing
- C. DNA fingerprinting
- D. Precipitin test (Correct Answer)
Explanation: ***Precipitin test*** - The **precipitin test** is used to determine the origin of a **blood sample**, specifically whether it is **human or animal blood**, by detecting species-specific proteins. It is not used for assessing maternity. - This test is primarily employed in **forensic serology** to differentiate between blood from different animal species, making it irrelevant for paternity or maternity disputes. *Blood grouping* - **Blood grouping** (e.g., ABO and Rh systems) can be used to **exclude paternity or maternity** by comparing the blood types of the child, mother, and alleged father. - If the child's blood type is incompatible with the alleged parents based on Mendelian inheritance, one or both can be excluded. *HLA typing* - **HLA typing** (Human Leukocyte Antigen) is a more powerful genetic marker system than ABO/Rh for determining paternity or maternity. - It involves analyzing highly polymorphic genes on chromosome 6 that encode cell surface proteins, providing a more definitive means of **inclusion or exclusion**. *DNA fingerprinting* - **DNA fingerprinting** (also known as **DNA profiling**) is the **most accurate and widely accepted method** for resolving paternity and maternity disputes. - It analyzes highly variable regions of DNA unique to each individual, providing a statistically strong basis for **inclusion or exclusion** by comparing genetic profiles.
Question 5: Phenylketonuria is due to a deficiency of:
- A. Phenylalanine hydroxylase (PAH) (Correct Answer)
- B. Galactokinase
- C. Tyrosinase
- D. Phenylalanine
Explanation: ***Phenylalanine hydroxylase (PAH)*** - **Phenylketonuria (PKU)** is an autosomal recessive disorder caused by a deficiency of the enzyme **phenylalanine hydroxylase (PAH)**. - This enzyme is crucial for converting the amino acid **phenylalanine** to **tyrosine**. *Phenylalanine* - Phenylalanine is the **substrate** that accumulates in PKU due to the enzyme deficiency, not the deficiency itself. - High levels of phenylalanine are **toxic** to the brain and lead to the clinical manifestations of PKU. *Galactokinase* - Deficiency of **galactokinase** is associated with **galactosemia type II**, a disorder of galactose metabolism. - This condition is characterized by **cataracts** and typically does not involve the neurologic symptoms seen in PKU. *Tyrosinase* - **Tyrosinase** deficiency is the primary cause of **oculocutaneous albinism type 1**, affecting melanin synthesis. - It results in hypopigmentation of the skin, hair, and eyes, which is unrelated to PKU.
Question 6: To assess thyroid profile of a newborn, which of the following is mandatory?
- A. Measure T3 only
- B. Measure TSH only
- C. Measure both TSH and T4 (Correct Answer)
- D. Measure T4 only
Explanation: ***Measure both TSH and T4*** - **Newborn screening** for congenital hypothyroidism typically involves measuring both **TSH** (thyroid-stimulating hormone) and **T4** (thyroxine). - Elevated TSH levels indicate **primary hypothyroidism**, where the thyroid gland is underactive, while low T4 levels confirm the reduced thyroid hormone production. *Measure T3 only* - **T3 (triiodothyronine)** is generally not the primary screening test for congenital hypothyroidism in newborns. - While T3 is an active form of thyroid hormone, its levels can be influenced by various factors and are less reliable than TSH and T4 for initial screening. *Measure TSH only* - Measuring only **TSH** can detect primary hypothyroidism, but it doesn't provide a complete picture of thyroid function. - In cases of **central (secondary or tertiary) hypothyroidism**, TSH levels might be normal or low, while T4 levels are reduced, which would be missed if only TSH were measured. *Measure T4 only* - Measuring only **T4** can help identify low thyroid hormone levels, but it doesn't differentiate between primary and central hypothyroidism. - To properly assess the cause of low T4, **TSH levels** are crucial to determine if the problem lies within the thyroid gland itself or higher up in the pituitary/hypothalamic axis.
Question 7: 34 week primigravida punjabi khatri comes with history of consanguineous marriage, with history of repeated blood transfusion to her sibling since 8 months of age. The first diagnostic test is -
- A. HPLC
- B. Bone marrow
- C. Blood smear
- D. Hb electrophoresis (Correct Answer)
Explanation: ***Hb electrophoresis*** - The patient's history of **consanguineous marriage**, a sibling requiring **repeated blood transfusions** since 8 months of age, and Punjabi Khatri ethnicity strongly suggest a **hemoglobinopathy**, likely **beta-thalassemia major or intermedia**. - **Hemoglobin electrophoresis** is the traditional gold standard for definitive diagnosis of various hemoglobin variants and thalassemia types, identifying and characterizing abnormal hemoglobin patterns (e.g., elevated HbF, HbA2). - It remains a primary diagnostic test for hemoglobinopathies, particularly useful for pattern recognition of various thalassemia syndromes. *HPLC* - **High-performance liquid chromatography (HPLC)** is an equally valid and increasingly preferred method for diagnosing hemoglobinopathies, offering automated, precise quantification of hemoglobin fractions (HbA, HbA2, HbF). - In modern practice, HPLC is often used as a first-line screening tool due to its accuracy, reproducibility, and ability to provide quantitative data crucial for thalassemia diagnosis. - Both HPLC and Hb electrophoresis are acceptable diagnostic approaches; the choice between them depends on laboratory availability and practice patterns. For this 2013 exam, Hb electrophoresis was considered the traditional first diagnostic test. *Blood smear* - A **peripheral blood smear** would show morphological changes like **microcytic hypochromic red blood cells**, **target cells**, **anisopoikilocytosis**, and **nucleated RBCs**, which are suggestive of thalassemia. - These findings are indicative but non-specific and require confirmatory tests like hemoglobin electrophoresis or HPLC to identify the specific hemoglobin disorder and establish a definitive diagnosis. *Bone marrow* - A **bone marrow** examination would show **erythroid hyperplasia** due to increased ineffective erythropoiesis in thalassemia but is an invasive procedure and not the initial diagnostic test for hemoglobinopathies. - It provides details about cellularity and maturation but does not directly identify hemoglobin abnormalities, making it unsuitable as the first diagnostic step in suspected hemoglobinopathies.
Question 8: 18 weeks pregnant female presents with no high risk of NTD and low risk of trisomy 21 on quad test. What is the most appropriate next step in management?
- A. Repeat non-invasive screening test.
- B. Perform invasive diagnostic testing.
- C. Perform amniotic fluid analysis.
- D. Perform a detailed fetal ultrasound. (Correct Answer)
Explanation: ***Perform a detailed fetal ultrasound.*** - A **detailed fetal ultrasound** (often referred to as an **anatomy scan**) at around 18-22 weeks is a standard component of prenatal care for all pregnant women, regardless of screening test results. - This ultrasound evaluates fetal anatomy for structural anomalies, assesses fetal growth, and confirms gestational age, providing crucial information even with low-risk screening. *Repeat non-invasive screening test.* - Repeating a non-invasive screening test (like another quad screen or NIPT) is generally **not indicated** when initial results show a low risk and there are no other clinical concerns. - Such tests are primarily for screening purposes, and a second low-risk result would offer little additional actionable information, as their positive predictive value is low. *Perform invasive diagnostic testing.* - **Invasive diagnostic testing**, such as **amniocentesis** or **chorionic villus sampling (CVS)**, carries a risk of miscarriage and is reserved for situations with a high risk of chromosomal abnormalities or genetic conditions. - Given the low-risk quad screen results for trisomy 21 and no high risk for NTDs, invasive testing is **not warranted** at this stage. *Perform amniotic fluid analysis.* - **Amniotic fluid analysis** is part of an amniocentesis, an **invasive diagnostic procedure** designed to detect chromosomal abnormalities or genetic disorders. - This procedure is typically reserved for cases where screening tests indicate a high risk or there is a clinical suspicion of a genetic condition; it's **not a routine step** after a low-risk quad screen.
Question 9: Which of the following statements regarding phenylketonuria (PKU) is false?
- A. Blood phenyl alanine level >20 mg/dl causes severe disease
- B. Neurological symptoms are due to deficiency of phenylalanine hydroxylase. (Correct Answer)
- C. Method of choice for screening is blood phenylalanine by Guthrie's test.
- D. PKU is caused by a deficiency of phenylalanine hydroxylase.
Explanation: ***Neurological symptoms are due to deficiency of phenylalanine hydroxylase.*** - This statement is **FALSE** - it confuses the cause with the mechanism. - Neurological symptoms in PKU are caused by the **accumulation of phenylalanine and its toxic metabolites** (such as phenylpyruvate, phenyllactate, and phenylacetate) in the brain, not directly by the enzyme deficiency itself. - The deficiency of **phenylalanine hydroxylase** is the underlying cause, but the **toxic buildup** is what damages the developing brain, leading to intellectual disability, seizures, and behavioral problems. *Blood phenyl alanine level >20 mg/dl causes severe disease* - This statement is **TRUE**. - Blood phenylalanine levels **>20 mg/dL** are diagnostic of **classical PKU**, which causes severe disease if untreated. - Normal phenylalanine levels are 1-2 mg/dL; levels >20 mg/dL require strict dietary management to prevent neurological damage. *Method of choice for screening is blood phenylalanine by Guthrie's test.* - This statement is **TRUE** in the traditional context taught for medical exams. - The **Guthrie bacterial inhibition assay** measures blood phenylalanine from a heel prick and has been the standard newborn screening method for decades. - While modern laboratories increasingly use **tandem mass spectrometry (MS/MS)**, the Guthrie test remains a validated and widely taught screening method. *PKU is caused by a deficiency of phenylalanine hydroxylase.* - This statement is **TRUE**. - **Phenylketonuria (PKU)** is an autosomal recessive disorder caused by mutations in the **PAH gene**, leading to deficiency of the enzyme **phenylalanine hydroxylase**. - This enzyme normally converts phenylalanine to tyrosine; its absence leads to phenylalanine accumulation.
Question 10: Increasing severity of intellectual disability of male members over generations is a result of ?
- A. Y linked disorder
- B. Frameshift mutation
- C. Trinucleotide repeat mutation (Correct Answer)
- D. Mitochondrial DNA mutation
Explanation: ***Trinucleotide repeat mutation*** - This phenomenon, known as **anticipation**, is characteristic of disorders caused by trinucleotide repeat expansions like **Fragile X syndrome**, where the number of repeats increases in successive generations, leading to earlier onset and more severe symptoms. - The expansion of these repeats often occurs during **meiosis**, particularly **oogenesis** for Fragile X, contributing to the increasing severity observed in offspring. *Y linked disorder* - Y-linked disorders affect only males and are passed from father to son, but they do not typically show increasing severity over generations or the phenomenon of anticipation. - Their inheritance pattern is straightforward and generally consistent across generations, without progressive phenotypic changes. *Frameshift mutation* - A **frameshift mutation** involves the insertion or deletion of nucleotides that are not multiples of three, leading to a shift in the reading frame and an altered protein sequence. - While they can cause severe genetic disorders, **frameshift mutations** do not typically explain the observed increase in severity across generations (anticipation). *Mitochondrial DNA mutation* - Mitochondria are inherited exclusively from the mother, and mutations in **mitochondrial DNA** can cause a range of disorders affecting energy production. - While these disorders can vary in severity due to **heteroplasmy**, they do not typically show a pattern of increasing severity in successive generations due to an expanding repeat sequence.
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