100+ Free ABMGG Clinical Biochemical Genetics Practice Questions

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A newborn screening result shows elevated phenylalanine on the dried blood spot. Which enzyme deficiency is the MOST common cause of this finding?

Dihydropteridine reductase deficiency

Phenylalanine hydroxylase deficiency

Tyrosine aminotransferase deficiency

GTP cyclohydrolase I deficiency

to track

2026 Statistics

Key Facts: ABMGG Clinical Biochemical Genetics Exam

150

Exam Questions

Plus 100-question General Exam

3.5 hrs

Exam Duration

3 blocks of 60 minutes

Content Domains

Per ABMGG Blueprint

$2,850+

Total Cost

Application + exams

Every 2 yrs

Exam Frequency

Odd years only

6 years

Eligibility Window

Max 3 attempts

The Clinical Biochemical Genetics specialty exam consists of 150 multiple-choice questions (single best answer) administered in 3 blocks of 50 questions with 60 minutes per block and 10-minute breaks between blocks. Candidates must also pass the 100-question ABMGG General Examination. The exam is offered every other year (odd years) at Pearson VUE centers. Total cost is approximately $2,850-$3,300 including application, general exam, and specialty exam fees.

Sample ABMGG Clinical Biochemical Genetics Practice Questions

Try these sample questions to test your ABMGG Clinical Biochemical Genetics exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1A newborn screening result shows elevated phenylalanine on the dried blood spot. Which enzyme deficiency is the MOST common cause of this finding?

A.Dihydropteridine reductase deficiency

B.Phenylalanine hydroxylase deficiency

C.Tyrosine aminotransferase deficiency

D.GTP cyclohydrolase I deficiency

Explanation: Phenylalanine hydroxylase (PAH) deficiency accounts for approximately 98% of cases of hyperphenylalaninemia detected on newborn screening. PAH converts phenylalanine to tyrosine, and its deficiency leads to classic phenylketonuria (PKU). Dihydropteridine reductase and GTP cyclohydrolase I deficiencies cause BH4-deficient hyperphenylalaninemia but are much rarer (1-2% of cases). Tyrosine aminotransferase deficiency causes tyrosinemia type II, not elevated phenylalanine.

2A 5-day-old infant presents with poor feeding, lethargy, and a distinctive sweet/burnt sugar odor. Plasma amino acid analysis shows markedly elevated leucine, isoleucine, and valine. What is the most likely diagnosis?

A.Phenylketonuria

B.Maple syrup urine disease

C.Isovaleric acidemia

D.Propionic acidemia

Explanation: Maple syrup urine disease (MSUD) is caused by deficiency of the branched-chain alpha-ketoacid dehydrogenase complex, leading to accumulation of the branched-chain amino acids leucine, isoleucine, and valine, along with their corresponding alpha-ketoacids. The characteristic sweet odor resembling maple syrup or burnt sugar is pathognomonic. PKU elevates phenylalanine only. Isovaleric acidemia and propionic acidemia are organic acidemias that present with metabolic acidosis and elevated specific organic acid markers.

3In a patient with suspected urea cycle disorder, which plasma amino acid finding is most consistent with ornithine transcarbamylase (OTC) deficiency?

A.Elevated citrulline

B.Elevated argininosuccinic acid

C.Low citrulline with elevated glutamine and alanine

D.Elevated arginine

Explanation: OTC deficiency is the most common urea cycle disorder. Because OTC catalyzes the condensation of carbamyl phosphate and ornithine to form citrulline, its deficiency results in low or absent citrulline. Glutamine and alanine accumulate as alternate nitrogen disposal pathways. Elevated citrulline suggests argininosuccinate synthetase deficiency (citrullinemia type I). Elevated argininosuccinic acid indicates argininosuccinate lyase deficiency. Elevated arginine suggests arginase deficiency.

4A 2-year-old child presents with developmental regression, seizures, and eczema. Urine organic acids show elevated phenylpyruvic acid and phenylacetic acid. Which dietary intervention is the mainstay of treatment?

A.Restriction of leucine intake

B.Restriction of phenylalanine intake with medical formula

C.High-protein diet supplementation

D.Supplementation with medium-chain triglycerides

Explanation: The findings are consistent with untreated or poorly controlled phenylketonuria (PKU). Phenylpyruvic acid and phenylacetic acid are phenylalanine metabolites that accumulate when phenylalanine hydroxylase is deficient. The mainstay of treatment is lifelong dietary restriction of phenylalanine using special medical formulas that provide all essential amino acids except phenylalanine. Leucine restriction is used in MSUD. High-protein diets would worsen PKU. MCT supplementation is used in long-chain fatty acid oxidation disorders.

5Which laboratory finding BEST distinguishes tyrosinemia type I from type II?

A.Elevated plasma tyrosine

B.Elevated urinary succinylacetone

C.Elevated urine 4-hydroxyphenylpyruvic acid

D.Elevated plasma methionine

Explanation: Succinylacetone is the pathognomonic biomarker for tyrosinemia type I (hepatorenal tyrosinemia, caused by fumarylacetoacetate hydrolase deficiency). It is not elevated in tyrosinemia type II (tyrosine aminotransferase deficiency) or type III. Both types I and II have elevated plasma tyrosine and urinary 4-hydroxyphenylpyruvic acid. Elevated methionine may occur in type I due to liver dysfunction but is nonspecific.

6A neonate with hyperammonemia has an elevated plasma glycine and low plasma citrulline. Urine orotic acid is markedly elevated. What is the most likely enzyme deficiency?

A.Carbamoyl phosphate synthetase I (CPS I)

B.Ornithine transcarbamylase (OTC)

C.N-acetylglutamate synthase (NAGS)

D.Argininosuccinate synthetase (ASS)

Explanation: Elevated urinary orotic acid with low citrulline and hyperammonemia is the classic biochemical pattern for OTC deficiency. In OTC deficiency, carbamyl phosphate accumulates and is shunted into the pyrimidine synthesis pathway, producing excess orotic acid. CPS I and NAGS deficiencies also cause hyperammonemia with low citrulline but do NOT cause elevated orotic acid because carbamyl phosphate is not produced in excess. ASS deficiency causes elevated citrulline.

7Which amino acid serves as the immediate precursor to nitric oxide synthesis?

A.Glutamine

B.Citrulline

C.Arginine

D.Ornithine

Explanation: Arginine is the direct substrate for nitric oxide synthase (NOS), which converts arginine to citrulline and nitric oxide (NO). Citrulline is a product of this reaction (and can be recycled back to arginine via argininosuccinate synthetase and lyase). Glutamine serves as a nitrogen carrier. Ornithine participates in the urea cycle but is not the direct precursor for NO synthesis.

8Nonketotic hyperglycinemia (glycine encephalopathy) is caused by a defect in which enzyme system?

A.Glycine cleavage system

B.Serine hydroxymethyltransferase

C.D-glyceric acid dehydrogenase

D.Glycine transaminase

Explanation: Nonketotic hyperglycinemia (NKH) is caused by deficiency of the glycine cleavage system (GCS), a mitochondrial multienzyme complex composed of P-protein (glycine decarboxylase), H-protein, T-protein, and L-protein. The defect leads to massive accumulation of glycine in plasma, CSF, and brain. An elevated CSF-to-plasma glycine ratio (>0.08) is the hallmark diagnostic finding. Serine hydroxymethyltransferase interconverts glycine and serine but is not the primary defect in NKH.

9A patient is diagnosed with classic homocystinuria. Which enzyme is deficient?

A.Methionine synthase

B.Cystathionine beta-synthase

C.Methylenetetrahydrofolate reductase

D.Betaine-homocysteine methyltransferase

Explanation: Classic homocystinuria is caused by cystathionine beta-synthase (CBS) deficiency, which catalyzes the condensation of homocysteine and serine to form cystathionine. This leads to elevated plasma homocysteine and methionine. Features include lens dislocation (ectopia lentis), intellectual disability, marfanoid habitus, and thromboembolism. Methionine synthase and MTHFR deficiencies cause homocysteine elevation with LOW methionine. Approximately 50% of CBS-deficient patients respond to pyridoxine (vitamin B6) supplementation.

10Which biochemical finding on plasma amino acid analysis helps distinguish CPS I deficiency from OTC deficiency?

A.Plasma ammonia level

B.Plasma citrulline level

C.Urinary orotic acid level

D.Plasma glutamine level

Explanation: Both CPS I and OTC deficiency present with hyperammonemia, low citrulline, and elevated glutamine. The distinguishing feature is urinary orotic acid: it is elevated in OTC deficiency (because excess carbamyl phosphate enters the pyrimidine pathway) but normal or low in CPS I deficiency (because carbamyl phosphate is not produced). Plasma ammonia and glutamine are elevated in both conditions. Citrulline is low in both.

About the ABMGG Clinical Biochemical Genetics Exam

The ABMGG Clinical Biochemical Genetics certification validates doctoral-level expertise in directing and interpreting biochemical laboratory analyses for diagnosing and managing inherited metabolic disorders. Diplomates demonstrate proficiency in inborn errors of metabolism, newborn screening, analytical techniques, and laboratory quality assurance.

Questions

150 scored questions

Time Limit

3.5 hours

Passing Score

Criterion-referenced

Exam Fee

$1,100 (specialty) + $1,000 (general) (American Board of Medical Genetics and Genomics (ABMGG))

ABMGG Clinical Biochemical Genetics Exam Content Outline

15%

Amino Acids

PKU, tyrosinemias, MSUD, urea cycle defects, homocystinuria, glycine encephalopathy, and sulfur amino acid disorders

13%

Lipids

Fatty acid oxidation disorders, hyperlipidemias, and cholesterol metabolism disorders including Smith-Lemli-Opitz and Niemann-Pick C

12%

Organic Acids

Methylmalonic acidemia, propionic acidemia, isovaleric acidemia, glutaric acidemia type I, and cobalamin defects

12%

Lysosomes

Mucopolysaccharidoses, sphingolipidoses (Gaucher, Fabry, Tay-Sachs), mucolipidoses, and Pompe disease

10%

Carbohydrates

Glycogen storage diseases, galactosemia, fructose metabolism disorders, and congenital disorders of glycosylation

Laboratory Methods

QA/QC, GC-MS, LC-MS/MS, enzyme assays, analyte quantification, regulatory compliance, and artifact recognition

Cofactors

Cobalamin metabolism disorders, biotinidase deficiency, molybdenum cofactor deficiency, and related vitamin cofactor disorders

Mitochondria

Mitochondrial myopathies, Leigh syndrome, electron transport chain disorders, mtDNA mutations, and depletion syndromes

16%

Other Domains

Peroxisomal disorders, purines/pyrimidines, transport defects, metals (Wilson/Menkes), neurotransmitters, creatine disorders, and other disease categories

How to Pass the ABMGG Clinical Biochemical Genetics Exam

What You Need to Know

Passing score: Criterion-referenced
Exam length: 150 questions
Time limit: 3.5 hours
Exam fee: $1,100 (specialty) + $1,000 (general)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ABMGG Clinical Biochemical Genetics Study Tips from Top Performers

1Focus heavily on amino acid disorders (15% of exam) — know PKU, MSUD, urea cycle defects, and their biochemical profiles inside and out

2Master the biochemical markers and lab findings for each disorder — the exam tests your ability to interpret real laboratory data

3Study the ABMGG Blueprint content outline thoroughly — it defines every testable disease and subtopic

4Know newborn screening panels and tandem mass spectrometry interpretation — this is tested across multiple domains

5Understand enzyme deficiencies and their downstream metabolic consequences — many questions require pathway knowledge

6Review emergency metabolic protocols for acute decompensation — treatment and management questions appear throughout

Frequently Asked Questions

What is the ABMGG Clinical Biochemical Genetics certification?

The ABMGG Clinical Biochemical Genetics certification is a specialty board certification from the American Board of Medical Genetics and Genomics. It validates expertise in directing and interpreting biochemical analyses for diagnosing inherited metabolic disorders. Diplomates are qualified to supervise clinical biochemical genetics diagnostic laboratories and serve as consultants on biochemical genetic disorders.

How many questions are on the ABMGG Biochemical Genetics exam?

The Clinical Biochemical Genetics specialty exam has 150 multiple-choice questions (single best answer) split into 3 blocks of 50 questions. You get 60 minutes per block with 10-minute breaks between blocks, totaling approximately 3.5 hours. Candidates must also pass the separate 100-question ABMGG General Examination.

What are the prerequisites for the ABMGG Biochemical Genetics exam?

You need an M.D., D.O., or Ph.D. in genetics, genomics, human genetics, or a related biological science field, plus satisfactory completion of full-time training in an ACGME-accredited laboratory genetics postdoctoral training program in Clinical Biochemical Genetics. International graduates must complete a credentials review and meet TOEFL-iBT requirements.

How often is the ABMGG Biochemical Genetics exam offered?

The Clinical Biochemical Genetics exam is offered every other year in odd years (2025, 2027, etc.) due to the smaller number of examinees needed for psychometric validity. Other ABMGG specialty exams are offered annually. The exam is administered at Pearson VUE testing centers in August.

What is the passing score for the ABMGG Biochemical Genetics exam?

The ABMGG uses a criterion-referenced standard-setting process where content experts define minimum competency. There is no fixed percentage or number of correct answers published as the passing score. A candidate who passes has demonstrated mastery of the knowledge, skills, and abilities associated with safe and effective patient care in biochemical genetics.

How much does the ABMGG Biochemical Genetics exam cost?

The total cost is approximately $2,850-$3,300. This includes the application fee ($750 for one specialty), General Examination fee ($1,000), and Specialty Examination fee ($1,100). A late application fee of $400 may apply. Payment is by ACH or credit/debit card (3% processing fee for cards).

What content domains are tested on the ABMGG Biochemical Genetics exam?

The exam covers 15 content domains: Amino Acids (15%), Lipids (13%), Organic Acids (12%), Lysosomes (12%), Carbohydrates (10%), Laboratory Methods (8%), Cofactors (7%), Mitochondria (7%), Peroxisomes (3%), Purines/Pyrimidines (3%), Transport (3%), Metals (3%), Neurotransmitters (2%), Creatine (1%), and Other Disease Categories (3%).

How long should I study for the ABMGG Biochemical Genetics exam?

Most candidates study for 6-12 months. Focus first on the highest-weighted domains: Amino Acids (15%), Lipids (13%), Organic Acids (12%), and Lysosomes (12%) make up over half the exam. Use the ABMGG content outline and blueprint, GeneReviews, and practice questions to guide your preparation.

What happens if I fail the ABMGG Biochemical Genetics exam?

If you fail, you must reapply for a future exam cycle. You have a maximum of 3 attempts within your 6-year board eligibility period. Since the Biochemical Genetics exam is only offered every other year, failed attempts can significantly impact your timeline. If you passed the General Exam but failed the specialty, you only need to retake the specialty exam.