Genetics LE5

Question 1

56. Autosomal dominant inheritance is characterized by all of the following EXCEPT:

a. It affects individuals in every generation.
b. There is a 50% chance of transmission if one parent is affected.
c. It affects males more commonly than females.
d. Phenotypically normal parents do not transmit the disease to their child.

Answer 1

C. It affects males more commonly than females.
Rationale: Autosomal dominant inheritance affects both males and females equally because the mutated gene is present on an autosome (non-sex chromosome). The key features include vertical transmission in every generation, a 50% chance of passing it on if one parent is affected, and the absence of transmission from phenotypically normal parents.

Question 2

57. Autosomal recessive disorders are characterized by all of the following EXCEPT:

a. Recurrence risk in siblings of 25%.
b. Increased incidence with consanguinity.
c. Greater incidence than that of autosomal dominant disorders.
d. Asymptomatic carrier state in parents.

Answer 2

C. Greater incidence than that of autosomal dominant disorders.
Rationale: Autosomal recessive disorders are generally less common than autosomal dominant disorders because both copies of the gene must be mutated to express the disease. Recurrence risk among siblings is 25%, consanguinity increases incidence, and carriers (heterozygous individuals) are asymptomatic.

Question 3

58. A disease affecting all of the daughters but none of the sons of an affected father, and 50% of the sons or daughters of an affected mother, is most likely:

a. X-linked recessive
b. X-linked dominant
c. Autosomal dominant
d. Autosomal recessive

Answer 3

B. X-linked dominant
Rationale: X-linked dominant inheritance leads to all daughters but no sons being affected if the father has the condition, while an affected mother has a 50% chance of passing it to either son or daughter.

Question 4

59. A disease passed on only through the mother and affecting both sons and daughters, with variable manifestations in the affected siblings, is most likely:

a. Mitochondrial inheritance
b. Multifactorial inheritance
c. X-linked recessive inheritance
d. X-linked dominant inheritance

Answer 4

A. Mitochondrial inheritance
Rationale: Mitochondrial disorders are inherited exclusively from the mother and can affect both males and females. The manifestations vary due to heteroplasmy, meaning different cells may have different amounts of mutated mitochondria.

Question 5

60. Uniparental disomy occurs when both copies of one chromosome come from the same parent. Which of the following statements about uniparental disomy is INACCURATE?

a. It can uncover/affect imprinting.
b. It can lead to some autosomal disorders.
c. It is associated with advanced maternal age.
d. It is associated with mosaicism for trisomy.

Answer 5

b. It can lead to some autosomal disorders.

Question 6

61. Polygenic (multifactorial) disorders result from the interplay of genetic and environmental factors. Which of the following is NOT typically considered a purely polygenic inheritance?

a. Cleft lip and palate
b. Spina bifida
c. Hypercholesterolemia
d. Hairy ears

Answer 6

D. Hairy ears
Rationale: Polygenic disorders result from multiple genes and environmental influences, as seen in cleft lip/palate, spina bifida, and hypercholesterolemia. Hairy ears, however, follow Y-linked inheritance and are not multifactorial.

Question 7

62. A child is born with an omphalocele. Omphalocele is a large abdominal wall defect that requires surgical correction. What is the most likely mechanism for this congenital anomaly?

a. Malformation
b. Deformation
c. Disruption
d. Dysplasia

Answer 7

A. Malformation
Rationale: A malformation results from an intrinsic defect in embryonic development, as seen in omphalocele, where the midgut fails to return to the abdominal cavity properly. Deformations result from mechanical forces, disruptions from external insults, and dysplasia from abnormal cellular organization.

Question 8

63. Which of the following studies is most useful in the diagnosis of aneuploidy?

a. Chromosomal karyotype
b. Fluorescent in situ hybridization (FISH)
c. Direct DNA analysis
d. Phenotypic study

Answer 8

A. Chromosomal karyotype
Rationale: Karyotyping is the most useful diagnostic test for detecting aneuploidy (abnormal chromosome number), such as trisomies (Down syndrome, Turner syndrome). FISH detects specific microdeletions, direct DNA analysis targets specific genes, and phenotypic studies are not diagnostic.

Question 9

64. The first-trimester non-invasive screening test with a good detection rate for aneuploidy is:

a. Ultrasound detection of nuchal
translucency
b. Amniocentesis
c. Chorionic villus sampling (CVS)
d. Combined screening (e.g. including nuchal translucency, PAPP-A, free β-hCG)

Answer 9

A. Ultrasound detection of nuchal translucency

Rationale: In the first trimester, nuchal translucency (NT) ultrasound is a key non-invasive screening tool for detecting aneuploidy, particularly trisomy 21 (Down syndrome), trisomy 18, and trisomy 13. It measures the fluid at the back of the fetal neck. When combined with maternal serum markers (PAPP-A and free β-hCG), detection rates improve.

Question 10

65. Which of the following is the most common inherited X-linked condition?

a. Fragile X syndrome
b. Rett syndrome
c. Hemophilia A
d. Color blindness

Answer 10

C. Hemophilia A

Rationale: Hemophilia A is the most common X-linked recessive disorder, caused by mutations in the F8 gene leading to Factor VIII deficiency. It primarily affects males, while females are typically carriers.

Question 11

66. Which of the following tests/studies is required to be done periodically in a child with Down syndrome (DS)?

a. Auditory testing
b. Visual assessment
c. 2D-Echocardiography
d. Thyroid function test

Answer 11

D. Thyroid function test
Rationale: Children with Down syndrome (DS) have an increased risk of congenital and acquired hypothyroidism, so periodic thyroid function tests (TSH, free T4) are recommended. While auditory testing, visual assessment, and 2D-Echo are also important in DS management, thyroid dysfunction is a frequent and treatable complication requiring routine screening.

Question 12

67. Williams syndrome results from a deletion of chromosome 7 that includes the elastin gene. All of the following are characteristic features of Williams syndrome EXCEPT:

a. Very friendly personality
b. Elfin facies
c. Normal IQ
d. Neonatal hypercalcemia

Answer 12

C. Normal IQ
Rationale: Williams syndrome is characterized by intellectual disability (IQ below average), an overly friendly personality, elfin facies (small upturned nose, wide mouth, full lips), and neonatal hypercalcemia due to elastin gene deletion on chromosome 7.

Question 13

68. Genetic diseases are caused by changes or mutations in the DNA sequence. A frameshift mutation refers to a:

a. Change in a single DNA base
b. Change in an amino acid of a particular protein
c. Increase in chromosomal number
d. Loss or addition of one or more DNA bases

Answer 13

D. Loss or addition of one or more DNA bases
Rationale: A frameshift mutation occurs when one or more nucleotide bases are inserted or deleted, shifting the reading frame and altering the downstream amino acid sequence. This often leads to nonfunctional proteins.

Question 14

69. A mentally retarded 15-year-old boy is found to have macrocephaly, large testes, and large, protruding ears. The most likely genetic diagnosis is:

a. Cerebral gigantism
b. Acromegaly
c. Fragile X syndrome
d. Trisomy 21 (Down syndrome)

Answer 14

C. Fragile X syndrome
Rationale: Fragile X syndrome is the most common inherited cause of intellectual disability. It presents with macrocephaly, large ears, a long face, and macroorchidism (enlarged testes in postpubertal males). It results from CGG trinucleotide repeat expansion in the FMR1 gene.

Question 15

70. Kearns-Sayre syndrome and Leber hereditary optic neuropathy are noted in both males and females but are inherited only through the mother. These conditions are examples of:

a. Uniparental disomy
b. Mitochondrial inheritance
c. X-linked dominant inheritance
d. X-linked recessive inheritance

Answer 15

B. Mitochondrial inheritance
Rationale: Kearns-Sayre syndrome (progressive external ophthalmoplegia, cardiac conduction defects) and Leber hereditary optic neuropathy (bilateral vision loss) are inherited only from the mother, characteristic of mitochondrial inheritance.

Question 16

71. FISH (Fluorescent In Situ Hybridization) in genetic testing is best described as:

a. A way to prepare RNA
b. An enzyme assay to detect mutations
c. Scraping of buccal cells (for DNA)
d. A test to identify the chromosomal location of a specific gene or sequence

Answer 16

D. A test to identify the chromosomal location of a specific gene or sequence
Rationale: Fluorescent In Situ Hybridization (FISH) uses fluorescent-labeled DNA probes to detect specific chromosomal abnormalities, such as deletions (e.g., 22q11 deletion in DiGeorge syndrome), duplications, and translocations.

Question 17

72. Trinucleotide repeats are implicated in the etiology of all of the following genetic disorders EXCEPT:

a. Fragile X syndrome
b. Neurofibromatosis
c. Friedreich ataxia
d. Myotonic dystrophy

Answer 17

B. Neurofibromatosis
Rationale: Trinucleotide repeat expansion disorders include:

Fragile X syndrome (CGG)
Friedreich ataxia (GAA)
Myotonic dystrophy (CTG)
Neurofibromatosis is caused by mutations in the NF1 or NF2 gene and does not involve trinucleotide repeats.

Question 18

73. A 1-year-old presents with a disease that is classically an autosomal recessive trait (such as cystic fibrosis). The father is tested and, with 99% confidence, is demonstrated to be negative for the carrier state. The most likely explanation is:

a. Mutation to an autosomal dominant trait
b. Uniparental isodisomy transmission from the mother
c. Uniparental isodisomy transmission from the father
d. Imprinting of the missing recessive gene (less likely, as it typically doesn’t change the genotype)

Answer 18

B. Uniparental isodisomy transmission from the mother
Rationale: Uniparental isodisomy occurs when both copies of a chromosome come from the same parent, which can lead to an autosomal recessive disorder if one parent is not a carrier. Since the father tested negative for the carrier state, maternal uniparental disomy is the most likely explanation.

Question 19

74. A newborn infant is noted to have dysmorphic features. The pregnancy was complicated by breech presentation, decreased fetal movements, and polyhydramnios. The infant demonstrates hypotonia, a flat face, flattened occiput, epicanthal folds, and abdominal distention. The most likely cause of this infant’s dysmorphology is:

a. Trisomy 13 (Patau syndrome)
b. Trisomy 18 (Edwards syndrome)
c. Trisomy 21 (Down syndrome)
d. Trisomy 8

Answer 19

C. Trisomy 21 (Down syndrome)
Rationale: Features of Down syndrome (Trisomy 21) include hypotonia, flat facies, epicanthal folds, a flattened occiput, and abdominal distension (often due to Hirschsprung disease or duodenal atresia). Pregnancy complications include polyhydramnios, breech presentation, and decreased fetal movements.

Question 20

75. A genetic condition which is lethal in infancy is most likely to be:

a. An X-linked structural protein
b. An autosomal recessive enzyme deficiency
c. An autosomal dominant enzyme deficiency
d. An autosomal dominant structural protein abnormality

Answer 20

B. An autosomal recessive enzyme deficiency
Rationale: Lethal genetic conditions in infancy are often autosomal recessive enzyme deficiencies, such as Tay-Sachs disease, Pompe disease, and certain urea cycle disorders. These conditions result in metabolic dysfunction, leading to severe symptoms and early death.

Question 21

76. You are evaluating a neonate with multiple dysmorphic features. You find him small for gestational age, microcephalic, with a single nostril, postaxial polydactyly, and rocker-bottom feet. The most likely diagnosis is:

a. Down syndrome
b. Williams syndrome
c. Edwards syndrome (Trisomy 18)
d. Patau syndrome (Trisomy 13)

Answer 21

D. Patau syndrome (Trisomy 13)
Rationale: Patau syndrome (Trisomy 13) is associated with microcephaly, holoprosencephaly (single nostril, cyclopia), postaxial polydactyly, rocker-bottom feet, and severe midline defects. It is a severe condition with high neonatal mortality.

Question 22

77. If there is a family history of genetic disorders, knowing the gender of an unborn child can be important because:

a. Male children are more likely to have autosomal defects show up in their phenotypes.
b. Female children are more likely to have autosomal defects show up in their phenotypes.
c. Male children are more likely to have X-linked traits show up in their phenotype.
d. (A) and (C) are correct.

Answer 22

D. (A) and (C) are correct.
Rationale:

Males are more likely to have autosomal defects show up in their phenotype due to the absence of a second X chromosome, which provides a backup copy of genes.
X-linked traits (both dominant and recessive) are more likely to be expressed in males, as they only have one X chromosome and lack a second copy to compensate for a mutation.

Question 23

78. All of the following are characteristic features of Turner syndrome EXCEPT:

a. Mildly affected IQ
b. Low-set ears
c. Puffiness of the hands and feet (lymphedema)
d. Webbing of the neck

Answer 23

A. Mildly affected IQ (typically normal IQ)
Rationale: Turner syndrome (45,X) typically presents with low-set ears, webbed neck, and puffy hands/feet (lymphedema at birth). Cognitive function is usually normal, though some may have learning difficulties in spatial reasoning and mathematics.

Question 24

79. What chromosomal disorder can present as bilateral cleft palate, cleft lip, and a ventricular septal defect?

a. Edwards syndrome
b. Turner syndrome
c. Down syndrome
d. Klinefelter syndrome

Answer 24

A. Edwards syndrome (Trisomy 18)
Rationale: Trisomy 18 (Edwards syndrome) is associated with cleft lip/palate, congenital heart defects (e.g., VSD), micrognathia, clenched hands, and rocker-bottom feet. It has a high neonatal mortality rate due to severe cardiac and respiratory complications.

Question 25

**80. A 10-month-old infant diagnosed with Trisomy 18 presents with a prominent occiput, clenched fists, and "rocker-bottom feet." What are two complications that can cause death in these children?** a. Sepsis and meningitis b. Heart failure and pneumonia c. DIC and CNS infection d. Disseminated TB and malnutrition

Answer 25

B. Heart failure and pneumonia Rationale: The leading causes of death in Trisomy 18 are congenital heart defects (leading to heart failure) and respiratory complications such as pneumonia due to poor immune function and hypotonia.

Question 26

**81. You are evaluating a 6-year-old boy with coarsened, gargoyle-like facial features, stiff joints, and a cloudy cornea. Of the following, the most likely genetic condition is:** a. Fragile X syndrome b. Hurler syndrome c. Huntington disease d. Friedreich ataxia

Answer 26

B. Hurler syndrome Rationale: Hurler syndrome (Mucopolysaccharidosis Type I, MPS I) presents with coarse facial features (gargoyle-like), corneal clouding, stiff joints, hepatosplenomegaly, and developmental delay due to α-L-iduronidase enzyme deficiency.

Question 27

**82. A 6-month-old infant presents to the ER with the following features: exaggerated startle reflex, hypotonia, loss of developmental milestones, and a cherry-red spot on the macula. You suspect Tay-Sachs disease. This neurodegenerative disease is best described as:** a. Having an adult-onset variety b. Having a single genetic defect c. Producing disease in only males d. Having a genetic defect in the hexosaminidase A enzyme

Answer 27

D. Having a genetic defect in the hexosaminidase A enzyme Rationale: Tay-Sachs disease is caused by a deficiency of hexosaminidase A, leading to GM2 ganglioside accumulation in neurons. It presents with progressive neurodegeneration, hypotonia, loss of milestones, exaggerated startle reflex, and a cherry-red spot on the macula.

Question 28

**83. Chromosome analysis should be ordered for children with:** a. Metabolic disorders b. Intellectual disability/Developmental delay c. Conotruncal heart defects d. Multiple congenital anomalies/Dysmorphia

Answer 28

D. Multiple congenital anomalies/Dysmorphia Rationale: Chromosomal analysis (e.g., karyotyping, FISH) is most useful in evaluating multiple congenital anomalies and dysmorphic syndromes, which suggest underlying chromosomal abnormalities such as Trisomy 13, Trisomy 18, or DiGeorge syndrome (22q11 deletion).

Question 29

**84. The MOST common genetic defect of Prader-Willi syndrome (PWS) is:** a. Deletion of maternal chromosome 15 (15q11-13) b. Deletion of paternal chromosome 15 (15q11-13) c. Paternal uniparental disomy of chromosome 15 d. Maternal uniparental disomy of chromosome 15

Answer 29

B. Deletion of paternal chromosome 15 (15q11-13) Rationale: Prader-Willi syndrome (PWS) is caused by a paternal deletion of 15q11-13 (70% of cases) or maternal uniparental disomy (25% of cases), leading to hypotonia, obesity, intellectual disability, and hyperphagia.

Question 30

**85. You are evaluating a 2-month-old baby boy with recurrent chest infections, cleft palate, right-sided aortic arch, and absent thymic shadow on CXR. He could be nominated as having one of the following syndromes EXCEPT:** a. Velocardiofacial syndrome b. Conotruncal anomaly face syndrome c. DiGeorge syndrome d. Pierre Robin syndrome

Answer 30

D. Pierre Robin syndrome Rationale: DiGeorge syndrome (22q11 deletion) includes recurrent infections (due to thymic hypoplasia), congenital heart defects (conotruncal anomalies), cleft palate, and hypocalcemia. Pierre Robin sequence involves micrognathia, cleft palate, and glossoptosis, but it is not associated with thymic or immune abnormalities.

Question 31

86. Of the following, the one which carries the highest rate of congenital heart disease is: a. Turner syndrome b. Williams syndrome c. Down syndrome d. Klinefelter syndrome

Answer 31

B. Williams syndrome Rationale: 🫀 Williams syndrome has the highest rate of congenital heart disease, most commonly supravalvular aortic stenosis. 🧬 Down syndrome is associated with AV septal defects but has a lower prevalence compared to Williams syndrome. 🎗️ Turner syndrome is linked to bicuspid aortic valve and coarctation of the aorta but at a lower rate. ⚧️ Klinefelter syndrome does not have a significant association with CHD.

Question 32

87. A two-week-old baby girl, delivered by NSD, term, AGA, was admitted due to poor suck and vomiting. Upon admission, the patient was lethargic with a classic mousy or musty odor of the urine. The Newborn Screening will likely test positive for: a. Homocystinuria b. Maple Syrup Urine Disease (MSUD) c. Phenylketonuria (PKU) d. Tyrosinemia type I

Answer 32

C. Phenylketonuria (PKU) Rationale: 👃 Mousy or musty odor is classic for PKU, due to the accumulation of phenylalanine. 🍼 Symptoms include poor feeding, vomiting, and lethargy due to toxic metabolite buildup. 🩺 PKU is detected in newborn screening to prevent intellectual disability through dietary management.

Question 33

88. In Maple Syrup Urine Disease, patients are unable to break down leucine, valine, and isoleucine because of a deficiency in this enzyme: a. Isovaleryl-CoA dehydrogenase (isovaleric acidemia) b. Branched-chain ketoacid decarboxylase c. Carbamoyl phosphate synthetase (hyperammonemia) d. Cystathionine synthase (homocystinuria)

Answer 33

B. Branched-chain ketoacid decarboxylase Rationale: 🌳 Maple Syrup Urine Disease (MSUD) results from a deficiency in branched-chain ketoacid decarboxylase, leading to leucine, valine, and isoleucine accumulation. 🍁 Sweet-smelling urine (like maple syrup) is a hallmark of MSUD. ⚠️ If untreated, leads to neurotoxicity, seizures, and early death.

Question 34

89. Organic acidemias are considered disorders of protein metabolism. Which of the following is NOT an organic acidemia? a. Maple Syrup Urine Disease b. Methylmalonic acidemia c. Lactic acidemia d. Propionic acidemia

Answer 34

C. Lactic acidemia Rationale: 🧪 Organic acidemias involve defective protein metabolism, leading to toxic acid buildup. ❌ Lactic acidemia is related to mitochondrial/energy metabolism, not organic acidemias. 🦠 Examples of organic acidemias: Maple Syrup Urine Disease Methylmalonic acidemia Propionic acidemia

Question 35

90. There are four pathologic pathways for inborn errors of metabolism. Which pathway affects mucopolysaccharidoses? a. Disorders causing accumulation of substrate or precursor b. Disorders resulting from a deficient product c. Disorders resulting from a disturbance of the breakdown of complex molecules d. Disorders involving energy generation

Answer 35

C. Disorders resulting from a disturbance of the breakdown of complex molecules Rationale: 💀 Mucopolysaccharidoses (e.g., Hurler and Hunter syndrome) result from defective lysosomal enzyme breakdown of glycosaminoglycans (GAGs). 🔬 Leads to progressive organ dysfunction, skeletal abnormalities, and neurodegeneration. 🛑 Accumulated GAGs cause multisystem damage.

Question 36

91. Characteristic odors are clues to the diagnosis of inborn errors of metabolism. What condition has a "sweaty feet" odor? a. Hawkinsinuria b. Trimethylaminuria c. Glutaric aciduria d. Isovaleric acidemia

Answer 36

D. Isovaleric acidemia Rationale: 👃 Sweaty feet odor is characteristic of Isovaleric acidemia, due to isovaleric acid accumulation. 🦠 Caused by a deficiency in isovaleryl-CoA dehydrogenase. ⚠️ Leads to metabolic acidosis, vomiting, and lethargy in infancy.

Question 37

92. A 6-year-old boy is brought to the OPD for consult regarding developmental delay. He was born full term via normal spontaneous delivery and normal at birth but has not been meeting his developmental milestones. He has a Marfanoid habitus and myopia. Which of the following is the most likely diagnosis? a. Homocystinuria b. Tyrosinemia c. Phenylketonuria d. Maple Syrup Urine Disease

Answer 37

A. Homocystinuria Rationale: 📏 Marfanoid habitus (tall stature, long limbs) and myopia suggest homocystinuria. 💉 Due to cystathionine-β-synthase deficiency, causing homocysteine accumulation. 🧠 Leads to developmental delay, intellectual disability, and thrombotic events.

Question 38

93. A 4-day-old neonate started to vomit after feeding. Upon physical examination, the following classic manifestations were noted: jaundice, cataract, hepatomegaly. What is the most likely enzyme deficiency involved? a. Galactokinase b. UDP Galactose 4-epimerase c. Galactose 1-phosphate uridyltransferase d. Lactate Dehydrogenase

Answer 38

C. Galactose 1-phosphate uridyltransferase Rationale: 👶 Classic galactosemia presents in neonates with jaundice, hepatomegaly, cataracts, and vomiting after milk feeding. 🍼 Caused by Galactose 1-phosphate uridyltransferase deficiency, leading to toxic galactose-1-phosphate buildup. 🚨 Early dietary restriction of lactose/galactose is crucial to prevent liver failure and neurotoxicity.

Question 39

94. A deficiency in the enzyme cystathionine-β-synthase will have classic Marfan-like manifestations with mental retardation, ectopia lentis, and thrombophlebitis. What is this condition? a. Trimethylaminuria b. Alkaptonuria c. Hawkinsinuria d. Homocystinuria

Answer 39

D. Homocystinuria Rationale: 🩺 Homocystinuria mimics Marfan syndrome with tall stature, ectopia lentis, and connective tissue involvement. 🧬 Caused by cystathionine-β-synthase deficiency, leading to homocysteine accumulation. ⚠️ Increases risk of thromboembolism, intellectual disability, and vascular complications.

Question 40

95. A lysosomal storage disorder with the accumulation of sphingolipid and β-glucocerebroside in the liver and spleen caused by a deficiency in the enzyme β-glucosidase is known as: a. Gaucher disease b. Fabry disease c. Krabbe disease d. Niemann-Pick disease

Answer 40

A. Gaucher disease Rationale: 🔬 Gaucher disease is a lysosomal storage disorder caused by β-glucosidase (glucocerebrosidase) deficiency, leading to sphingolipid accumulation. 🩸 Hepatosplenomegaly, pancytopenia, bone pain, and "Gaucher cells" in bone marrow are key features. 🛑 Treated with enzyme replacement therapy (ERT).

Question 41

96. A senile-like appearance syndrome associated with infertility, incomplete sexual maturation, and accelerated aging is known as: a. Porphyria b. Tay-Sachs disease c. Progeria d. Adrenoleukodystrophy

Answer 41

C. Progeria (Hutchinson-Gilford progeria syndrome) Rationale: 👴 Progeria is a rare genetic disorder characterized by accelerated aging, growth retardation, and senile-like appearance. 🧬 Caused by a mutation in the LMNA gene, leading to defective lamin A protein. 🚫 Patients exhibit incomplete sexual maturation and infertility but have normal intelligence.

Question 42

97. Mucopolysaccharidoses is an abnormal accumulation of glycosaminoglycans in connective tissue. A type of mucopolysaccharidosis with a deficiency of the enzyme iduronate-2-sulfatase is known as: a. Hurler syndrome b. Morquio disease c. Hunter syndrome d. Sanfilippo disease

Answer 42

C. Hunter syndrome Rationale: 🧬 Hunter syndrome (MPS II) is a mucopolysaccharidosis caused by a deficiency in iduronate-2-sulfatase, leading to glycosaminoglycan accumulation. ❌ Unlike Hurler syndrome, Hunter syndrome does not cause corneal clouding. 🛑 X-linked recessive inheritance, affecting mostly males.

Question 43

98. A 16-year-old male presented with delayed puberty, tall stature, gynecomastia, eunuchoid proportions, small testes, and intellectual disability. This condition is known as: a. Kallmann syndrome b. Prader-Willi syndrome c. Fragile X syndrome d. Klinefelter syndrome

Answer 43

D. Klinefelter syndrome Rationale: ⚧️ Klinefelter syndrome (47,XXY) presents with tall stature, gynecomastia, small testes, and infertility due to testosterone deficiency. 🧠 Mild intellectual disability and social difficulties may occur. 🩺 High FSH and LH with low testosterone.

Question 44

99. A 1-week-old male newborn is brought to the ER because of vomiting and poor feeding for 3 days. On exam, he is jaundiced and has hepatomegaly. Urine reducing substance is positive. The most likely diagnosis is: a. Galactosemia b. Gaucher disease c. Niemann-Pick disease d. Hunter syndrome

Answer 44

A. Galactosemia Rationale: 🍼 Galactosemia presents with vomiting, jaundice, hepatomegaly, and poor feeding in neonates after consuming breast milk or formula containing lactose. 🔬 Urine reducing substance test is positive due to galactose buildup. 🚨 Caused by Galactose-1-phosphate uridyltransferase (GALT) deficiency and requires immediate lactose-free diet.

Question 45

100. You are evaluating a 6-year-old boy with coarsened, gargoyle-like facial features, stiff joints, and a cloudy cornea in the ER. What is the most likely genetic condition of this patient? a. Hunter syndrome b. Hurler syndrome c. Gaucher disease d. Tay-Sachs disease

Answer 45

B. Hurler syndrome Rationale: 🧬 Hurler syndrome (MPS I) is caused by α-L-iduronidase deficiency, leading to glycosaminoglycan accumulation. 👹 Features include coarse (gargoyle-like) facial features, corneal clouding, joint stiffness, and hepatosplenomegaly. 🚨 Progressive neurodegeneration, often leading to early death if untreated.