Board Exam Biochemical Practice Questions

Front 1

New parents bring their 1-week-old baby boy to the pediatrician's office and report that he is not feeding as well over the last 24 hours and that his diapers have an odor like sweaty feet. Which of the following disorders is the most likely cause of this child's problems?
A. Isovaleric acidemia B. Maple syrup urine disease C. Methylmalonic acidemia D. Phenylketonuria E. Propionic acidemia

Back 1

A

Front 2

B2. Which of the following laboratory tests is most likely to provide a definitive diagnosis?
Metabolic Panel B. Plasma amino acids C. Plasma ammonium level D. Urine amino acids E. Urine organic acids

Back 2

E.

Front 3

B3. A six-month-old boy presents with hepatomegaly, renomegaly, hypoglycemia and lactic acidosis. Which GSD enzyme deficiency is correct?
A. Type la is glucose-6-phosphatase deficiency or von Gierke. B. Type II is (alpha-glucosidase (acid maltase) deficiency or Pompe. C. Type III is debrancher deficiency or Forbes. D. Type V is muscle phosphorylase deficiency or McArdle

Back 3

A

Front 4

B.4 A six-month-old boy presents with severe hypotonia, massive cardiomegaly, progressive weakness and markedly elevated CPK. Which GSD enzyme deficiency is correct?
A. Type la is glucose-6-phosphatase deficiency or von Gierke. B. Type II is (alpha-glucosidase (acid maltase) deficiency or Pompe. C. Type III is debrancher deficiency or Forbes. D. Type V is muscle

Back 4

B

Front 5

B.5 A four-day-old infant boy is brought to the emergency room lethargic and no longer taking his formula. A metabolic profile reveals metabolic acidosis and his ammonium level is normal. Which of the following diagnoses is most likely to be found with subsequent metabolic screening studies? A. Citrullinemia B. Maple syrup urine disease C. Methylmalonic acidemia D. Ornithine transcarbamylase deficiency E. Proprionic acidemia

Back 5

B. High ammonia would be a feature of all of these disorders except maple syrup urine disease.

Front 6

B6.A 6 year old girl is referred to genetics following an episode of pancreatitis. During her hospitalization, she received hyperalimentation and became obtunded. An ammonia level during this episode was 200 meq/L. Following discontinuation of the hyperalimentation and treatment of the pancreatitis, the girl was discharged home on a low fat diet. She has not had any further episodes of pancreatitis or lethargy. You suspect she has a specific metabolic disorder. Which of the following laboratory evaluations is the BEST way to obtain a specific diagnosis? A. Gene sequencing B. Plasma amino acids C. Plasma ammonia level D. Protein challenge E. Urine orotic acid

Back 6

A. The clinical vignette is suspicious for heterozygous OTC deficiency. Female carriers can become symptomatic when ill or if they receive a high protein load (such as hyperalimentation). In the past, a protein challenge or allopurinol loading test followed by measurement of urine orotic acid was often used to make a diagnosis. Today gene sequencing is the best method. Urine orotic acid alone or ammonia level will not be abnormal unless the patient is in the midst of an acute crisis.

Front 7

B7. You are seeing a couple whose first child is a Duarte/classical Galactosemia genetic compound heterozygote. His parents (who have not been tested) ask about the risk for their next child to have classical galactosemia (Gal/Gal). Knowing that the frequencies of the Duarte (1/27) and Gal (1/278) alleles, which of the following do you think is their risk to have a Gal/Gal child? A. 1/278 B. 1/278 x 2/3 C. 1/278 x1⁄2 D. 1/278 x 2/3 x 1⁄2 E. 1/278 x1⁄2x1⁄2

Back 7

E. One parent must be a Gal carrier and the other a Duarte carrier. There is a possibility that the parent who is a Duarte carrier is also a Gal carrier. Such individuals have about 25% of normal gal activity, which would not produce clinical signs of galactosemia. The risk that the other allele in this parent is Gal is 1/278. In this case the risk to a child would be 1⁄4. Therefore the overall risk is 1/278 x 1⁄4.

Front 8

B8. You are notified by the state newborn screening laboratory that a seven-day-old neonate, born at 33-weeks gestation and is receiving antibiotics for possible sepsis and total parenteral nutrition (TPN). He was found to have a phenylalanine level (Phe) of 4.8 mg/dL (291 (M). Which of the following interventions is the most appropriate next step in evaluating or managing this child's care? A. Stop (TPN) briefly and remeasure Phe on glucose and IV fluids. B. Modify antibiotic coverage patient is probably receiving C. Monitor the phenylalanine level weekly over next month. D. Restrict the infant's phenylalanine intake E. Obtain urine for assessment of biopterin metabolite levels

Back 8

A. There are two reasons why this infant may have an elevated phe on newborn screening – immaturity of the HPPD enzyme and TPN. The best way to exclude an inherited disorder in phe metabolism would be to stop the TPN briefly (~4-6 hr) and provide calories with glucose and recheck the phe off the TPN.

Front 9

B9. A 3 year old boy is referred to genetics clinic for evaluation of hypotonia, seizures, and developmental delay. His older brother, age 8, was also hypotonic and has been diagnosed with autism. You suspect a disorder of creatine metabolism. Which of the following studies is the best option to confirm a diagnosis for this child? A. Measure plasma guanidinoacetoacetate B. Measure plasma creatine to creatinine ratio C. Perform a brain MRI D. Perform plasma amino acids to measure an ornithine level E. Sequence the SLC6A8 creatine transporter gene

Back 9

E. The history is fairly classic for X-linked creatine transporter deficiency which can account for up to ~1% of X-linked MR. Other features include hypotonia, seizures, and autism. Screening can be performed by urine guanidinoacetoacetate (GAA) which is elevated or by finding a low creatine peak on brain MRI with spectroscopy. It is not specific on plain MRI. While the disorder is technically a defect in ornithine metabolism, ornithine levels are normal. Plasma creatine/creatinine ratio is used to detect the 2 other disorders of creatine metabolism (AGAT and GAMT deficiency).

Front 10

B10. A nine- month-old infant contracts a viral illness and is unable to take her usual amount of formula over the previous 24 hours. She is found dead in her bed the following morning. Which of the following disorders accounts for approximately 5% of cases of sudden infant death syndrome (SIDS) and is the most likely cause of this unfortunate infant’s death? A. Glutaric aciduria Type I B. Glycogen storage disease Type III C. MCAD deficiency D. OTC deficiency E. Propionic academia

Back 10

C. MCAD presents with hypoketotic hypoglycemia and can resemble Reye syndrome or SIDs.