Metabolic disorders overview — MCQs

A 6-month-old boy is brought to the emergency department by his mother because of recurrent vomiting and yellowing of his eyes. The mother says that he has been eating poorly since she started weaning him off of breast milk 5 days ago. At this time, mashed vegetables and fruits were added to his diet. Examination shows scleral jaundice and dry mucous membranes. The tip of the liver is palpable 4 cm below the right costal margin. His serum glucose concentration is 47 mg/dL, serum alanine aminotransferase is 55 U/L, and serum aspartate aminotransferase is 66 U/L. Which of the following enzymes is most likely deficient?

A 2-year-old boy is brought to the emergency department by his mother 30 minutes after having a generalized tonic-clonic seizure. He was born at home and has not attended any well-child visits. He is not yet able to walk and does not use recognizable words. His paternal uncle has a severe intellectual disability and has been living in an assisted-living facility all of his life. The boy's urine phenylacetate level is markedly elevated. Which of the following amino acids is most likely nutritionally essential for this patient because of his underlying condition?

A mother brings her 3-year-old daughter to the pediatrician because she is concerned about her development. She states that her daughter seemed to regress in her motor development. Furthermore, she states she has been having brief episodes of uncontrollable shaking, which has been very distressing to the family. During the subsequent work-up, a muscle biopsy is obtained which demonstrates red ragged fibers and a presumptive diagnosis of a genetic disease is made. The mother states that she has another 6-year-old son who does not seem to be affected or have any similar symptoms. What genetic term explains this phenomenon?

A 3-week-old newborn is brought to the pediatrician by his mother. His mother is concerned about her son’s irritability and vomiting, particularly after breastfeeding him. The infant was born at 39 weeks via spontaneous vaginal delivery. His initial physical was benign. Today the newborn appears mildly jaundiced with palpable hepatomegaly, and his eyes appear cloudy, consistent with the development of cataracts. The newborn is also in the lower weight-age percentile. The physician considers a hereditary enzyme deficiency and orders blood work and a urinalysis to confirm his diagnosis. He recommends that milk and foods high in galactose and/or lactose be eliminated from the diet. Which of the following is the most likely deficient enzyme in this metabolic disorder?

An 18-month-old boy of Ashkenazi-Jewish descent presents with loss of developmental milestones. On ocular exam, a cherry-red macular spot is observed. No hepatomegaly is observed on physical exam. Microscopic exam shows lysosomes with onion-skin appearance. What is the most likely underlying biochemical abnormality?

An 8-month-old female infant from a first-degree consanguineous couple was brought to the physician because the mother noticed abnormalities in the growth of her child as well as the different lengths of her child's legs. The infant had gingival hyperplasia, restricted movement in both shoulders, a prominent, pointed forehead, and enophthalmos with a slight opacity in both corneas. A blood test revealed 10 fold higher than normal levels of the following enzymes: N-acetyl-ß-glucosaminidase, ß-glucuronidase, ß-hexosaminidase A, and alkaline phosphatase. Which of the following is most likely deficient in this patient?

You are counseling a mother whose newborn has just screened positive for a deficit of phenylalanine hydroxylase enzyme. You inform her that her child will require dietary supplementation of which of the following?

A 2-day-old newborn boy is brought to the emergency department because of apnea, cyanosis, and seizures. He is severely hypoglycemic and does not improve with glucagon administration. His blood pressure is 100/62 mm Hg and heart rate is 75/min. Blood tests show high lactate levels. Physical examination is notable for hepatomegaly. Which of the following enzymes is most likely to be deficient in this baby?

A 7-month-old boy is brought to the pediatrician for a change in his behavior. The patient has been exclusively breastfeeding up until this point and has been meeting his developmental milestones. He is in the 90th percentile for weight and 89th percentile for height. Two weeks ago, his parents began introducing weaning foods including fruit purees and baby formula. This past week, the patient has been increasingly lethargic, vomiting, and has been refusing to eat. The patient's parents state that he had an episode this morning where he was not responsive and was moving his extremities abnormally followed by a period of somnolence. The patient's past medical history is notable for shoulder dystocia and poorly managed maternal diabetes during the pregnancy. His temperature is 99.5°F (37.5°C), blood pressure is 60/30 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. On physical exam, you note a lethargic infant with a distinctive sweet, fruity smell to his breath. Which of the following is most likely deficient in this patient?

A 4-year-old boy is brought to the physician for a well-child examination. He started walking at 20 months of age. He can use a cup to drink but cannot use silverware. He speaks in 2-word sentences and can build a tower of 4 blocks. He can scribble but cannot draw a circle. He is above the 99th percentile for height and at the 15th percentile for weight. Vital signs are within normal limits. Examination shows bilateral inferior lens dislocation. His fingers are long and slender. He has a high-arched palate. The thumb and 5th finger overlap when he grips a wrist with the opposite hand. The skin over the neck can be extended and stretched easily. Which of the following is the most likely cause of these findings?