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LMBRD1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

LMBRD1 gene

The LMBRD1 gene provides instructions for making a protein essential for transporting vitamin B12 within cells and regulating insulin signaling.

Normal Function

The LMBRD1 gene provides instructions for making a protein called LMBD1. This protein is involved in the conversion of vitamin B12 (cobalamin) into two specific molecules: adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl).

AdoCbl acts as a cofactor for the enzyme methylmalonyl CoA mutase, which helps break down certain amino acids, fats (lipids), and cholesterol. MeCbl acts as a cofactor for the enzyme methionine synthase, which converts the amino acid homocysteine to methionine, a building block for proteins.

The LMBD1 protein is located in the membrane of lysosomes, which are cellular compartments that digest and recycle materials. Within this membrane, LMBD1 interacts with the ABCD4 protein to transport vitamin B12 out of the lysosome, making it available for processing into AdoCbl and MeCbl.

Additionally, LMBD1 is found in the plasma membrane, where it helps remove the insulin receptor to regulate insulin signaling and blood glucose levels. A version of the protein called NESI may also aid in the assembly of the hepatitis D virus.

Health Conditions Related to Genetic Changes

Methylmalonic acidemia with homocystinuria

Variants in the LMBRD1 gene can cause methylmalonic acidemia with homocystinuria, cblF type. This condition is associated with developmental delay, eye defects, neurological problems, and blood abnormalities.

  • Mechanism: Genetic variants lead to the production of an abnormally short, non-functional LMBD1 protein.
  • Impact: Without functional LMBD1, vitamin B12 remains trapped in lysosomes and cannot be converted into AdoCbl or MeCbl.
  • Consequences: The enzymes methylmalonyl CoA mutase and methionine synthase fail to function, leading to a buildup of toxic compounds and homocysteine, alongside a decrease in methionine production.

Other Names for This Gene

  • bA810I22.1
  • C6orf209
  • cblF
  • FLJ11240
  • HDAg-L-interacting protein NESI
  • hepatitis delta antigen-L interacting protein
  • liver regeneration p-53 related protein
  • LMBD1
  • MAHCF
  • NESI
  • nuclear export signal-interacting protein
  • probable lysosomal cobalamin transporter

Frequently Asked Questions

In addition to hydroxocobalamin injections, a low‑protein diet that limits propiogenic amino acids (isoleucine, valine, methionine, threonine) can help reduce methylmalonic acid accumulation. Some clinicians also limit odd‑chain fatty acids and supplement with carnitine if levels are low. Dietary management should be individualized by a metabolic dietitian.
Many state newborn screening programs include a measurement of elevated propionyl‑carnitine (C3) or methylmalonic acid, which can flag cblF type methylmalonic acidemia with homocystinuria caused by LMBRD1 mutations. Follow‑up confirmatory testing includes plasma amino acids, urine organic acids, and molecular genetic analysis of the LMBRD1 gene.
Carriers (heterozygotes) are typically asymptomatic because one functional copy of LMBRD1 provides enough protein for normal B12 transport. No routine monitoring is needed unless there is a family history of metabolic disease; genetic counseling is recommended for family planning.
High‑dose hydroxocobalamin is given by intramuscular injection (often 1 mg daily initially, then tapered to weekly or monthly maintenance) to bypass the lysosomal transport defect. Early treatment can reduce metabolic crises, improve growth, and lessen neurologic damage, but lifelong therapy is usually required.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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