D51.1 - Vitamin B12 Deficiency Anaemia with Proteinuria
D51.1 is the ICD-10 code for vitamin B12 deficiency anaemia due to selective vitamin B12 malabsorption with proteinuria, also known as Imerslund-Grasbeck syndrome, a rare inherited disorder.
Things worth knowing about "D51.1"
D51.1 is the ICD-10 code for vitamin B12 deficiency anaemia due to selective vitamin B12 malabsorption with proteinuria, also known as Imerslund-Grasbeck syndrome, a rare inherited disorder.
Definition and ICD-10 Code D51.1
D51.1 is the ICD-10 code for vitamin B12 deficiency anaemia due to selective vitamin B12 malabsorption with proteinuria, also known as Imerslund-Grasbeck syndrome (IGS). This is a rare, autosomal recessive inherited condition in which the absorption of vitamin B12 in the intestine is impaired, accompanied by increased excretion of protein in the urine (proteinuria).
Causes
The disorder is caused by mutations in the CUBN (cubilin) or AMN (amnionless) genes. These genes encode proteins that together form the cubilin-amnionless complex (CubAM complex), which is essential for:
- The absorption of vitamin B12 (bound to intrinsic factor) in the terminal ileum of the small intestine
- The reabsorption of proteins in the renal tubules
When the CubAM complex is non-functional, vitamin B12 cannot be properly absorbed from the gut, and proteinuria develops due to impaired tubular reabsorption in the kidneys.
Symptoms
Symptoms typically appear in infancy or early childhood and include:
- Anaemia: Fatigue, pallor, weakness, and shortness of breath
- Megaloblastic anaemia: Enlarged, immature red blood cells visible on blood smear
- Neurological symptoms: Developmental delay, tingling in the hands and feet, muscle weakness
- Proteinuria: Elevated urinary protein excretion, usually without significant impairment of kidney function
- Failure to thrive: Poor weight gain and growth in affected children
Diagnosis
Diagnosis is based on a combination of clinical and laboratory findings:
- Blood count: Megaloblastic anaemia with low serum vitamin B12 levels
- Urine analysis: Detection of proteinuria, particularly low-molecular-weight proteins
- Schilling test: Demonstrates impaired intestinal vitamin B12 absorption (less commonly used in modern clinical practice)
- Genetic testing: Molecular confirmation of mutations in the CUBN or AMN gene
- Intrinsic factor antibodies: Negative, to exclude pernicious anaemia (D51.0)
Treatment
Treatment consists of lifelong vitamin B12 supplementation, as the underlying genetic defect cannot be cured:
- Intramuscular vitamin B12 injections: Bypasses the defective intestinal absorption mechanism; this is the preferred treatment approach
- High-dose oral vitamin B12: In some cases, a small amount of vitamin B12 can be absorbed passively through the intestinal mucosa
With regular vitamin B12 supplementation, anaemia and neurological symptoms improve significantly. Proteinuria typically persists but generally does not lead to progressive kidney damage.
Differentiation from Other Vitamin B12 Deficiency Anaemias
ICD-10 code D51.1 must be distinguished from other subtypes of vitamin B12 deficiency anaemia:
- D51.0: Vitamin B12 deficiency anaemia due to intrinsic factor deficiency (pernicious anaemia)
- D51.2: Vitamin B12 deficiency anaemia due to transcobalamin II deficiency
- D51.3: Nutritional vitamin B12 deficiency anaemia
References
- Grasbeck R. - Imerslund-Grasbeck syndrome (selective vitamin B12 malabsorption with proteinuria). Orphanet Journal of Rare Diseases, 2006; 1:17. doi:10.1186/1750-1172-1-17
- Fyfe JC et al. - The functional cobalamin (vitamin B12)-intrinsic factor receptor is a novel complex of cubilin and amnionless. Blood, 2004; 103(5):1573-1579.
- World Health Organization (WHO) - ICD-10 International Statistical Classification of Diseases and Related Health Problems, 10th Revision, Code D51.1.
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