Free MBG Practice Questions

Question 1

A 3-day-old boy becomes obtunded after a day of poor feeding. Two properly handled plasma samples show ammonia concentrations of 640 and 780 µmol/L, 60 minutes apart. Initial testing shows respiratory alkalosis, very low citrulline, and markedly increased urinary orotate. He has been intubated; natural protein has been temporarily withheld, and intravenous dextrose, arginine, and sodium benzoate-sodium phenylacetate have been started. What is the most urgent addition to his treatment?

Accepted Answer

Begin urgent extracorporeal ammonia clearance.

Answer

Give a second full loading dose of the intravenous nitrogen scavengers.

Answer

Increase arginine delivery and assess the ammonia response over two hours.

Answer

Trial carglumic acid before deciding whether extracorporeal clearance is necessary.

Question 2

For the third time in two years, a 27-year-old man develops painful muscle weakness and dark urine after several hours of hiking with little food. Brief, intense exercise is usually tolerated, and his strength and creatine kinase are normal between attacks. During this episode, creatine kinase is 31,000 U/L and plasma acylcarnitines show predominant C16 and C18:1 elevations without an increased C14:1. Deficiency of which enzyme best fits the trigger pattern and biochemical findings?

Accepted Answer

Carnitine palmitoyltransferase II

Answer

Muscle glycogen phosphorylase

Answer

Very-long-chain acyl-CoA dehydrogenase

Answer

Carnitine palmitoyltransferase I

Question 3

Metabolic testing in a 9-week-old infant with poor growth and hypotonia shows markedly increased methylmalonic acid and total homocysteine, with methionine below the age-specific reference interval. Serum vitamin B12 is within the laboratory reference interval; maternal methylmalonic acid and total homocysteine are normal. Samples for molecular confirmation have been sent. Which initial regimen addresses both abnormal metabolic pathways?

Accepted Answer

Parenteral hydroxocobalamin with betaine

Answer

Oral cyanocobalamin with a methionine-restricted formula

Answer

Pyridoxine with methionine restriction and cysteine supplementation

Answer

Biotin and precursor-protein restriction

Question 4

Enzyme replacement is being planned for a 6-week-old infant with hypotonia, hypertrophic cardiomyopathy, and confirmed acid alpha-glucosidase deficiency. Before the first infusion, an antibody-based protein assay detects no endogenous GAA protein, establishing CRIM-negative status. How should this result change the initial treatment strategy?

Accepted Answer

Coordinate prompt enzyme replacement with preemptive immune-tolerance induction.

Answer

Start enzyme replacement; add immune modulation only if antibodies persist.

Answer

Delay enzyme replacement for several weeks while completing immune-tolerance induction.

Answer

Use antihistamine premedication alone to prevent antibody-mediated loss of treatment efficacy.

Question 5

A milk-fed newborn was admitted with jaundice, coagulopathy, and Escherichia coli sepsis. Antibiotics and a galactose-restricted formula were started, and packed red cells were transfused for significant anemia. The only erythrocyte GALT activity sample was collected after transfusion and is reported as normal. No pretransfusion specimen is available. The infant is now clinically improved, and the parents ask about restarting breast milk. Which feeding plan is justified while the diagnosis is resolved?

Accepted Answer

Continue galactose-restricted formula while obtaining molecular confirmation of the suspected diagnosis.

Answer

Restart breast milk because the normal GALT activity excludes classic galactosemia.

Answer

Restart breast milk after a second normal erythrocyte GALT assay next week.

Answer

Introduce small breast-milk feeds and use erythrocyte galactose-1-phosphate to test tolerance.

Question 6

An amino-acid assay is monitored with the original Westgard multirule procedure. Today's low-concentration control is 2.3 standard deviations above its established mean; the high-concentration control is 0.4 standard deviations above its mean. During the preceding ten runs, all controls were within one standard deviation; both control levels were below their means in the immediately preceding run. Calibration is unchanged and no other quality concerns are identified. Which disposition follows this quality-control system?

Accepted Answer

Accept the run and continue the established quality-control schedule.

Answer

Reject the run because the isolated 1₂s event is a rejection rule.

Answer

Recalibrate the assay because the controls establish a positive systematic shift.

Answer

Repeat the outlying control until it returns within two standard deviations.

Question 7

At 18 weeks of pregnancy, a woman with diet-treated phenylalanine hydroxylase deficiency reports that she reduced her natural-protein allowance below the prescribed amount because she feared fetal injury. Her last three phenylalanine concentrations were 58, 66, and 61 µmol/L. Review confirms adequate calories and full intake of her phenylalanine-free medical food. What adjustment should the metabolic dietitian recommend?

Accepted Answer

Increase prescribed natural protein toward a phenylalanine concentration of 120-360 µmol/L.

Answer

Maintain phenylalanine below 120 µmol/L through delivery to minimize fetal exposure.

Answer

Stop the phenylalanine-free medical food while keeping her current natural-protein intake unchanged.

Answer

Keep the current diet until phenylalanine exceeds 360 µmol/L on two successive samples.

Question 8

A term infant is evaluated for vomiting and lethargy on day 8. Pretreatment studies show high-anion-gap metabolic acidosis, ketonuria, and hyperammonemia. Propionylcarnitine (C3) is markedly elevated. Urine contains abundant 2-methylcitrate, 3-hydroxypropionate, and propionylglycine, but methylmalonic acid is not elevated; total plasma homocysteine is also normal. The biochemical block most consistent with these results prevents which conversion?

Accepted Answer

Propionyl-CoA to methylmalonyl-CoA

Answer

Methylmalonyl-CoA to succinyl-CoA

Answer

3-Methylcrotonyl-CoA to 3-methylglutaconyl-CoA

Answer

Isovaleryl-CoA to 3-methylcrotonyl-CoA

Question 9

A 38-year-old woman has sensorineural hearing loss, diabetes, and recurrent episodes of visual disturbance with cortical MRI lesions that cross arterial territories. Her mother and maternal uncle also have diabetes and hearing loss. Blood testing for common mitochondrial DNA variants, including MT-TL1 m.3243A>G, is negative. She would prefer another noninvasive test before considering muscle biopsy. Which investigation best addresses the limitation of the blood result?

Accepted Answer

Test mitochondrial DNA from urinary epithelial cells for heteroplasmic variants.

Answer

Quantify mitochondrial DNA copy number in peripheral leukocytes.

Answer

Sequence POLG and TWNK without further mitochondrial DNA analysis.

Answer

Repeat the same blood assay when her serum lactate is elevated.

Question 10

A 17-year-old with persistently elevated aminotransferases is assessed for Wilson disease. Ceruloplasmin is 0.07 g/L, and an adequately collected 24-hour urine contains 160 µg copper (laboratory upper limit, 40 µg/24 h). There is no acute hepatitis, cholestasis, hemolysis, neurologic abnormality, or Kayser-Fleischer ring. ATP7B testing identifies one pathogenic variant and a variant of uncertain significance on the other allele. No liver biopsy has been performed. How should the Leipzig score be assigned and interpreted?

Accepted Answer

5 points: the diagnosis is established by the scoring criteria.

Answer

3 points: further diagnostic evidence is needed.

Answer

8 points: the two ATP7B findings establish biallelic pathogenicity.

Answer

5 points: hepatic copper measurement is required before the diagnosis can be established.

Free MBG Practice Questions

Domain 1: Amino acids 15% of exam

Question 1

Question 2

Domain 2: Organic acids 12% of exam

Question 3

Domain 3: Cofactors 7% of exam

Question 4

Domain 4: Carbohydrates 10% of exam

Question 5

Domain 5: Lipids 13% of exam

Question 6

Domain 6: Lysosomes 12% of exam

Question 7

Domain 7: Mitochondria 7% of exam

Question 8

Domain 13: Metals 3% of exam

Question 9

Domain 14: Laboratory 8% of exam

Question 10

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