- What This Cheat Sheet Covers (and What It Doesn't)
- The Blueprint at a Glance: 15 Categories, Weighted
- The Heavy Hitters: Amino Acids, Lipids, Organic Acids
- Second-Tier Domains: Carbohydrates, Lysosomes, Mitochondria, Cofactors
- Small Domains That Still Show Up
- The Laboratory Domain: QA/QC, Artifacts, Techniques, Regulations
- One-Page Pattern Recognition Grid
- Exam Logistics You Can Verify
- Turning the Weights into a Study Sequence
- Frequently Asked Questions
- The blueprint has 15 content categories; Amino acids (15%), Lipids (13%), and Organic acids (12%) lead the weighting.
- Lysosomes (12%) and Carbohydrates (10%) round out the biggest domains, so five areas carry most of the exam.
- The published percentages total 102% because of a source discrepancy; treat them as approximate guides, not exact counts.
- Next administration is August 2027, since biochemical genetics specialties are offered in odd years.
What This Cheat Sheet Covers (and What It Doesn't)
This page compresses the Clinical Biochemical Genetics (CBG) content outline into a single scannable review. The content is drawn from the American Board of Medical Genetics and Genomics (ABMGG) Biochemical Genetics Blueprint and Content Codes, effective August 2025. If you are still orienting yourself, start with our explainers on what CBG is and CBG requirements and eligibility, then come back here for the review layer.
One note on sourcing: the ABMGG index page references 2026 outlines, while the blueprint document supplied for this review is effective August 2025. Always confirm the current version on the ABMGG content outlines page before you finalize your plan.
The Blueprint at a Glance: 15 Categories, Weighted
Here is the full domain map with the approximate published weights. The figures sum to 102%, a discrepancy inherited from the source document. They are preserved as published rather than normalized, so read them as relative emphasis.
| # | Domain | Approx. Weight |
|---|---|---|
| 1 | Amino acids | 15% |
| 2 | Organic acids | 12% |
| 3 | Cofactors | 7% |
| 4 | Carbohydrates | 10% |
| 5 | Lipids | 13% |
| 6 | Lysosomes | 12% |
| 7 | Mitochondria | 7% |
| 8 | Peroxisomes | 3% |
| 9 | Purines and pyrimidines | 3% |
| 10 | Transport | 3% |
| 11 | Creatine | 1% |
| 12 | Neurotransmitters | 2% |
| 13 | Metals | 3% |
| 14 | Laboratory | 8% |
| 15 | Other disease category | 3% |
For a deeper walk through every category, see the complete guide to all 15 CBG content areas.
The Heavy Hitters: Amino Acids, Lipids, Organic Acids
Together these three domains account for roughly 40% of the published weighting. If your time is limited, they are where fluency pays off most.
Domain 1: Amino Acids (15%)
The single largest domain. Expect to connect a clinical picture, an analyte pattern, and a management principle for each disorder.
- PKU and hyperphenylalaninemia: know how it separates from biopterin-related causes (a cross-over with the Cofactors domain).
- Tyrosinemias: distinguish the types by enzyme, organ involvement, and characteristic markers.
- Glycine encephalopathy/hyperglycinemia: recognize the neonatal presentation and the biochemical hallmark.
- MSUD and branched-chain amino acid disorders: classic odor, characteristic amino acid elevations, and decompensation triggers.
- Homocystinuria, sulfur amino acids, and re-methylation: differentiate remethylation defects from transsulfuration defects using methionine and homocysteine behavior.
- Urea cycle defects: ammonia, orotic acid, citrulline, and arginine patterns for each enzyme step.
- Other/Serine: do not skip the serine biosynthesis disorders.
Domain 5: Lipids (13%)
The second-heaviest domain, and a mix of fatty acid oxidation, lipoprotein disorders, and sterol biochemistry.
- Fatty acid oxidation disorders: short-chain, medium-chain, long-chain, and multiple acyl-CoA dehydrogenase deficiency (GA2). Learn the acylcarnitine signature for each.
- Hyperlipidemias: including Tangier disease and other disorders of lipid transport.
- Cholesterol metabolism: Smith-Lemli-Opitz syndrome, Niemann-Pick C, and other bile acid disorders.
Domain 2: Organic Acids (12%)
Organic acid disorders reward pattern recognition across urine organic acids and acylcarnitine profiles.
- Methylmalonic acidemia (excluding cobalamin defects) and propionic acidemia: note that cobalamin-related forms are tested under Cofactors.
- 3-MCC deficiency and other C5OH-related disorders and IVA and other C5-related disorders: the C5 and C5OH acylcarnitine species are a classic differential exercise.
- Glutaric acidemia type I: recognize the neurologic risk and the key markers.
- Ketone body disorders: HMG-CoA lyase deficiency and SCOT deficiency.
- Other: glutathione synthetase deficiency, ECHS1, and 3-methylglutaconic aciduria (non-type 1).
Key Takeaway
The blueprint deliberately splits related disorders across domains. Methylmalonic acidemia sits in Organic acids, but its cobalamin variants sit in Cofactors. Build cross-reference notes so you never study a disorder in only one place.
Second-Tier Domains: Carbohydrates, Lysosomes, Mitochondria, Cofactors
Domain 6: Lysosomes (12%)
Large and detail-dense, with many named entities that are easy to confuse.
- Mucopolysaccharidoses: Types I, II, III, IV, VI, and VII. Memorize the enzyme, the accumulating glycosaminoglycan, and the inheritance pattern (MPS II is the X-linked one).
- Sphingolipidoses: Gaucher disease, Fabry disease, GM2 gangliosidoses (Tay-Sachs disease and variants, Sandhoff disease), Krabbe disease, Niemann-Pick types A and B, GM1 gangliosidosis.
- Multiple enzyme deficiencies: mucolipidoses ML-II and ML-III, multiple sulfatase deficiency.
- Other: Pompe disease, cystinosis, and the NCLs. Note that GSD II is cross-referenced here rather than under Carbohydrates.
Domain 4: Carbohydrates (10%)
- Glycogenoses (except GSD II, which lives under Lysosomes).
- Glycolysis and gluconeogenesis disorders, including fructose-1,6-bisphosphatase deficiency.
- Galactose and fructose metabolism disorders: know the enzyme steps and the dietary implications.
- Congenital disorders of glycosylation: transferrin isoform interpretation is a recurring concept.
- Other: including the pentose phosphate pathway.
Domain 7: Mitochondria (7%)
- Mitochondrial myopathies, split by laboratory findings, Leigh syndrome, and adult presentations.
- Electron transport chain function and assembly disorders.
- mtDNA mutation disorders, mtDNA maintenance disorders, and mtDNA depletion syndromes.
- Other, including MELAS.
Domain 3: Cofactors (7%)
- Cobalamin, biotin, molybdenum, folate, pyridoxine, and biopterin.
- Other cofactors including riboflavin, niacin, and thiamine.
- Focus on which disorders are treatable by cofactor supplementation, since that is a natural exam angle.
Small Domains That Still Show Up
Low weight does not mean zero risk. Several small categories contain high-yield, easily memorized facts that are good value per hour of study.
- Peroxisomes (3%): biogenesis disorders such as Zellweger syndrome; single-enzyme disorders such as X-linked adrenoleukodystrophy; and others including Refsum (infantile).
- Purines and pyrimidines (3%): Lesch-Nyhan disease, adenosine deaminase deficiency, and UMP synthase deficiency, plus related disorders.
- Transport (3%): dibasic aminoaciduria (cystinuria, lysinuric protein intolerance), other amino acid transport disorders, glucose, carnitine, and other transporters.
- Metals (3%): copper (Wilson disease, Menkes disease, and others), iron, zinc, and other metals.
- Neurotransmitters (2%): SSADH deficiency, dopamine synthesis disorders, and other GABA metabolism disorders.
- Creatine (1%): a single-line category on the blueprint, worth a short, focused review.
- Other disease category (3%): a catch-all, so keep a running list of disorders that do not fit neatly elsewhere.
The Laboratory Domain: QA/QC, Artifacts, Techniques, Regulations
At 8%, the Laboratory domain is larger than Peroxisomes, Purines and pyrimidines, Transport, Metals, Neurotransmitters, and Creatine combined. It tests whether you can run and interpret the testing, not only name the disease. The four published subtopics are:
- QA/QC: quality assurance and quality control practices in a biochemical genetics laboratory.
- Artifact: recognizing results that look pathological but arise from specimen handling, medication, diet, or analytical interference.
- Techniques: the analytical methods used for amino acids, organic acids, acylcarnitines, and enzyme or other biochemical assays.
- Regulations: the regulatory framework governing clinical laboratory testing.
Candidates with a clinical rather than laboratory background often under-prepare this section. If that describes you, schedule it early rather than saving it for the end.
One-Page Pattern Recognition Grid
The most efficient review format for this exam is a matrix of disorder family versus the lab signal that points to it. Use the grid below as a template and fill in the specifics from your own references.
| Disorder Family | Primary Sample Type to Review | Concept to Master |
|---|---|---|
| Amino acid disorders | Plasma amino acids | Which amino acid is elevated or depleted, and the pathway step it implies |
| Urea cycle defects | Plasma amino acids, urine orotic acid, ammonia | Differentiating enzyme blocks by citrulline, arginine, and orotic acid |
| Organic acidemias | Urine organic acids, acylcarnitine profile | C3, C5, and C5OH species and their disease associations |
| Fatty acid oxidation disorders | Acylcarnitine profile | Chain-length-specific acylcarnitine signatures, including GA2 patterns |
| Lysosomal storage disorders | Enzyme assays, urine glycosaminoglycans | Enzyme, substrate, and inheritance for each MPS and sphingolipidosis |
| Congenital disorders of glycosylation | Transferrin isoform analysis | Interpreting abnormal glycoform patterns |
| Peroxisomal disorders | Very long chain fatty acids and related markers | Biogenesis versus single-enzyme patterns |
| Cofactor disorders | Variable by cofactor | Which defects respond to supplementation |
Key Takeaway
For every disorder, be able to state four things without hesitation: the enzyme or transporter, the key analyte pattern, the inheritance pattern, and the headline treatment principle. Apply that four-part template across all fifteen domains.
Exam Logistics You Can Verify
Several logistics worth knowing are confirmed in the ABMGG materials, while others are not established in the sources behind this article.
- Issuer: the American Board of Medical Genetics and Genomics (ABMGG).
- Timing: biochemical genetics specialties are offered in odd years, so the next CBG exam is in August 2027. ABMGG has also published an exam-dates announcement for 2027 and news about moving toward an annual certifying examination schedule, so check the ABMGG site for the latest.
- Not established here: the exact question count, timer, fee, and passing score were not available in the supplied official source content, so this article does not state them. Verify each on the ABMGG site before planning around them.
For related planning topics, see our pages on CBG exam dates and scheduling, CBG certification cost, and the CBG passing score. If you want a read on difficulty, our guide to how hard the CBG exam is covers what makes it demanding, and the CBG pass rate page explains what is and is not publicly known.
Turning the Weights into a Study Sequence
This is the only methodology section in this article, and it is tied directly to the blueprint. The logic: start with the foundational biochemistry that other domains reuse, then move to the heaviest domains, then sweep the small ones.
Foundations and Laboratory
- Review the Laboratory domain (QA/QC, artifacts, techniques, regulations) early, since analytical logic supports everything else.
- Study Cofactors next, because cobalamin, biotin, and biopterin explain variants in Amino acids and Organic acids.
The Heavy Hitters
- Amino acids, including urea cycle defects.
- Organic acids, then Lipids and fatty acid oxidation, using acylcarnitine patterns as the connecting thread.
Storage and Energy Domains
- Lysosomes with a flashcard table of enzyme, substrate, and inheritance.
- Carbohydrates and Mitochondria.
Small Domains and Integration
- Peroxisomes, Purines and pyrimidines, Transport, Metals, Neurotransmitters, Creatine, and Other.
- Cross-domain review of split disorders such as methylmalonic acidemia and GSD II.
For a fuller approach to preparation, including how to structure review around the content outline, read our CBG study guide. When you are ready to test your recall under realistic conditions, use the CBG practice tests to find weak domains, and the full practice test library to drill them.
Frequently Asked Questions
Amino acids is the largest at approximately 15%, followed by Lipids at 13%, and Organic acids and Lysosomes at 12% each. Carbohydrates follows at 10%.
The published approximate percentages (15, 12, 7, 10, 13, 12, 7, 3, 3, 3, 1, 2, 3, 8, and 3) total 102% because of a discrepancy in the source document. They are presented as published rather than adjusted, so treat them as relative emphasis rather than exact question counts.
The next CBG exam is identified as August 2027, because biochemical genetics specialties are offered in odd years. ABMGG has also announced a transition toward annual certifying examinations, so confirm current scheduling on the ABMGG website. See our exam dates guide for more.
No. Those details were not established from the supplied official source content, so they are intentionally omitted rather than guessed. Confirm them directly with ABMGG, and see our pages on certification cost and passing score for context.
No. The blueprint categories are exam objectives, not a substitute for broader preparation resources or performance-only training. Use a one-page review to confirm recall and spot gaps, and build depth through textbooks, cases, and practice questions.