Inborn Errors of Metabolism

Topics in this chapter

• Amino Acid Disorders
• Urea Cycle and Hyperammonemia
• Glycogen Storage Diseases
• Fructose and Carbohydrate Disorders
• Lysosomal Storage Diseases
• Peroxisomal and Lipid Disorders

Practice questions

1. Question 1Q-44730B

   A 6-month-old infant is brought to the pediatric clinic with a history of recurrent vomiting, lethargy, and seizures after the introduction of fruit juices into the diet. Laboratory evaluation reveals hypoglycemia and hyperuricemia without hepatomegaly. Which of the following enzyme deficiencies is responsible for this condition?

   1. A.Glucose-6-phosphatase
   2. B.Aldolase B
   3. C.Galactose-1-phosphate uridyltransferase
   4. D.Myophosphorylase
   See the answer and solution
2. Question 2Q-2086FD

   A 5-day-old neonate presents with poor feeding, lethargy, vomiting, and a sweet, maple syrup-like odor to the urine. Laboratory tests show severe metabolic acidosis with an increased anion gap and ketosis. This disorder is caused by a defect in the metabolism of which of the following groups of amino acids?

   1. A.Aromatic amino acids (Phenylalanine, Tyrosine)
   2. B.Branched-chain amino acids (Leucine, Isoleucine, Valine)
   3. C.Sulfur-containing amino acids (Methionine, Cysteine)
   4. D.Acidic amino acids (Aspartate, Glutamate)
   See the answer and solution
3. Question 3Q-BD2A31

   A 3-year-old child presents with coarse facial features, skeletal abnormalities (dysostosis multiplex), cloudy corneas, and restricted joint mobility. Laboratory evaluation of cultured fibroblasts shows deficient activity of alpha-L-iduronidase. Which of the following accumulated substances is primarily responsible for the clinical findings?

   1. A.Glycogen
   2. B.Sphingomyelin
   3. C.Dermatan sulfate and Heparan sulfate
   4. D.Keratan sulfate and GM2 ganglioside
   See the answer and solution
4. Question 4Q-36351F

   An 8-year-old boy is evaluated for joint pain, particularly in the lower back and large joints. Physical examination reveals a bluish-black discoloration of the sclerae and ear cartilage (ochronosis). His urine turns dark upon standing and exposure to air. A defect in which of the following enzymes is responsible for this condition?

   1. A.Phenylalanine hydroxylase
   2. B.Homogentisate 1,2-dioxygenase
   3. C.Tyrosinase
   4. D.Fumarylacetoacetate hydrolase
   See the answer and solution
5. Question 5Q-1F5413

   A 9-month-old infant is brought to the clinic for delayed developmental milestones and hypotonia. Examination reveals a 'cherry-red spot' on the macula and an exaggerated startle response to acoustic stimuli (hyperacusis). Hepatosplenomegaly is notably absent. Which of the following enzyme deficiencies is the most likely cause?

   1. A.Sphingomyelinase
   2. B.Glucocerebrosidase
   3. C.Hexosaminidase A
   4. D.Alpha-galactosidase A
   See the answer and solution