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MTRR gene

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

MTRR gene

The MTRR gene provides instructions for the methionine synthase reductase enzyme, which is necessary to keep the methionine synthase enzyme active.

Normal Function

The MTRR gene provides instructions for making an enzyme called methionine synthase reductase. This enzyme is required for the proper function of methionine synthase, which converts the amino acid homocysteine into methionine. Because methionine synthase naturally becomes inactive after a period of activity, methionine synthase reductase is required to reactivate it so the conversion process can continue.

Health Conditions Related to Genetic Changes

Homocystinuria

At least 20 mutations in the MTRR gene have been identified in people with homocystinuria. These mutations can change single amino acids or lead to the production of an abnormally small, nonfunctional enzyme. Without functional methionine synthase reductase, methionine synthase cannot convert homocysteine to methionine. This leads to a buildup of homocysteine in the bloodstream and a reduction in methionine levels, with some excess homocysteine being excreted in the urine.

Other disorders

A specific version (variant) of the MTRR gene, written as A66G, replaces the nucleotide adenine with guanine at a specific location. This variant has been associated with:

  • Neural tube defects: An increased risk of birth defects affecting the development of the brain and spinal cord.
  • Down syndrome: A potential increase in the risk of having a child with Down syndrome, a condition characterized by intellectual disability and associated health problems.

Other Names for This Gene

  • cblE
  • methionine synthase reductase
  • MSR
  • MTRR_HUMAN

Frequently Asked Questions

Common early signs include developmental delays, vision problems, and a tendency for blood clots. Parents may also notice a child having a higher than normal red blood cell count or unexplained fatigue. If these symptoms appear, a doctor may order a homocysteine level test and a genetic screen for MTRR mutations.
Diagnosis starts with a blood test measuring homocysteine and methionine levels. Elevated homocysteine with low methionine suggests a defect in the methionine synthase pathway. A follow‑up DNA test that looks for known MTRR mutations confirms the diagnosis.
Patients are usually advised to limit methionine intake (found in high‑protein foods) and increase folate and vitamin B12, which help the body convert homocysteine to methionine. A dietitian can design a low‑methionine diet and recommend supplements to keep homocysteine levels in check.
MTRR mutations are inherited in an autosomal recessive pattern, meaning both parents must carry a mutation for a child to be affected. Couples can undergo carrier testing before conception. If both are carriers, options include prenatal testing, pre‑implantation genetic diagnosis, or using donor gametes to avoid passing the mutation.===
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.