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Inherited errors of cobalamin metabolism and their management
1Vitamin B12 Unit, Chelsea and Westminster Hospital, London, UK.
Bailliere'S Clinical Haematology
|September 1, 1995
Summary
Inherited cobalamin metabolism disorders affect nutrient absorption and utilization, leading to serious health issues like megaloblastic anemia and developmental delay. Early diagnosis and treatment with specific cobalamin coenzymes are crucial for managing these genetic conditions.
Area of Science:
- Biochemistry
- Genetics
- Metabolic Disorders
Background:
- Cobalamins (vitamin B12) are essential coenzymes synthesized by microorganisms but utilized by mammalian cells for critical metabolic pathways.
- Defects in cobalamin absorption, transport, or intracellular metabolism result in inherited disorders, often presenting with severe clinical manifestations.
- Two key coenzyme forms, adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl), are vital for mitochondrial and cytosolic functions, respectively.
Purpose of the Study:
- To review the molecular basis, clinical presentation, diagnosis, and management of inherited cobalamin metabolism disorders.
- To highlight the importance of recognizing these rare but serious genetic conditions for timely intervention.
Main Methods:
- Analysis of inherited cobalamin metabolism defects, including genetic mutations affecting intrinsic factor (IF), transcobalamin II (TCII), and cobalamin-dependent enzymes.
- Diagnostic approaches involving urine and plasma assays for methylmalonic acid and homocysteine, and cobalamin coenzyme analysis.
- Utilizing fibroblast studies to differentiate between closely related metabolic defects.
Main Results:
- At least 12 distinct mutations (cblA-G) are known, impacting various stages of cobalamin processing.
- Biochemical markers like elevated methylmalonic acid and homocysteine indicate metabolic dysfunction.
- Clinical manifestations range from megaloblastic anemia to neurological deficits, with potential for normal serum B12 levels in some cases (e.g., TCII deficiency).
Conclusions:
- Early diagnosis of inborn errors of cobalamin metabolism is critical, especially in newborns presenting with anemia or developmental issues.
- Prompt treatment, potentially including specific coenzyme therapy (e.g., methylcobalamin), can significantly improve outcomes and prevent irreversible damage.
- Understanding the distinct roles of AdoCbl and MeCbl guides therapeutic strategies for different metabolic defects.