Genetic Disorders

Topics in this chapter

• Genetic Inheritance Patterns
• Newborn Screening and Diagnosis
• Amino Acid Metabolism Disorders
• Carbohydrate and Organic Acid Disorders
• Lysosomal Storage Disorders
• Trace Metal Metabolism Disorders
• Heritable Connective Tissue Disorders
• X-Linked Neuromuscular Disorders

Practice questions

1. Question 1Q-F98145

   A 5-year-old boy is brought to the outpatient clinic with a history of recurrent respiratory tract infections, chronic diarrhea, and failure to thrive. On examination, he has sparse, twisted, silvery-gray hair (pili torti), hypotonia, and progressive neurological deterioration. Serum copper and ceruloplasmin levels are markedly decreased. Which of the following is the most likely diagnosis?

   1. A.Menkes disease
   2. B.Wilson disease
   3. C.Cystic fibrosis
   4. D.Phenylketonuria
   See the answer and solution
2. Question 2Q-588DD3

   A 2-day-old term newborn is evaluated for lethargy, poor feeding, and tachypnea. Laboratory investigations reveal a severe high anion gap metabolic acidosis, hyperammonemia with normal plasma citrulline levels, and ketosis. Urine analysis shows massive excretion of methylcitric acid and propionylcarnitine. Which of the following is the most likely enzyme deficiency?

   1. A.Phenylalanine hydroxylase
   2. B.Propionyl-CoA carboxylase
   3. C.Ornithine transcarbamylase
   4. D.Glucose-6-phosphatase
   See the answer and solution
3. Question 3Q-5341C6

   A 3-year-old child presents with global developmental delay, coarse facial features, restricted joint mobility, and corneal clouding. X-ray of the spine reveals lumbar kyphosis with anterior beaking of the L1 or L2 vertebrae. Leukocyte enzyme assay confirms a deficiency of alpha-L-iduronidase. Which of the following mucopolysaccharidoses does this child have?

   1. A.Hurler syndrome (MPS I)
   2. B.Hunter syndrome (MPS II)
   3. C.Sanfilippo syndrome (MPS III)
   4. D.Morquio syndrome (MPS IV)
   See the answer and solution
4. Question 4Q-1D7469

   A 6-month-old infant is brought to the pediatrician for developmental regression, hypotonia, and an exaggerated startle response to sudden noises. Fundoscopic examination reveals a cherry-red spot in the macula. Hepatosplenomegaly is notably absent. Which of the following is the most likely underlying biochemical defect?

   1. A.Glucocerebrosidase deficiency
   2. B.Hexosaminidase A deficiency
   3. C.Sphingomyelinase deficiency
   4. D.Alpha-galactosidase A deficiency
   See the answer and solution
5. Question 5Q-94A3F3

   A 4-year-old boy is evaluated for progressive muscle weakness, frequent falls, and difficulty rising from the floor, for which he uses his hands to walk up his thighs (Gowers sign). Examination shows calf pseudohypertrophy. Serum creatine kinase (CK) levels are extremely elevated. Genetic testing reveals a deletion in the dystrophin gene. What is the classic mode of inheritance for this condition?

   1. A.Autosomal dominant
   2. B.Autosomal recessive
   3. C.X-linked recessive
   4. D.Mitochondrial inheritance
   See the answer and solution