Traits

Traits linked to MTRR

5-methyltetrahydrofolate-homocysteine methyltransferase reductase

The Human Phenotype Ontology links 63 traits to MTRR, by body system: features seen in people with one of the gene's rare conditions.

Abnormality of the nervous system

Trait	How often it is seen
Global developmental delay	Always
Abnormal cerebral white matter morphology	Often (30–79%)
Abnormal speech pattern	Often (30–79%)
Abnormality of movement	Often (30–79%)
Brain degeneration	Often (30–79%)
Decrease in size of the outer layer of the brain due to loss of brain cells	Often (30–79%)
Drowsiness	Often (30–79%)
Epilepsy	Often (30–79%)
Hyperactive movements	Often (30–79%)
Intellectual disability	Often (30–79%)
Loss of consciousness	Often (30–79%)
Severe global developmental delay	Often (30–79%)
Behavioral abnormality	Sometimes (5–29%)
Delayed myelination	Sometimes (5–29%)
Excessive daytime sleepiness	Sometimes (5–29%)
Lethargy	Sometimes (5–29%)
Peripheral neuropathy	Sometimes (5–29%)
Small brainstem	Sometimes (5–29%)
Too much cerebrospinal fluid in the brain	Sometimes (5–29%)
Ventriculomegaly	Sometimes (5–29%)
Widened subarachnoid space	Sometimes (5–29%)
Abnormal gait	Not recorded
Degeneration of cerebrum	Not recorded
Spinal dysraphism	Not recorded

Abnormality of blood and blood-forming tissues

Trait	How often it is seen
Megaloblastic anemia	Always
Normocytic anemia	Always
Megaloblastic bone marrow	Very often (80–99%)
Increased mean corpuscular volume	Often (30–79%)
Macrocytic anemia	Often (30–79%)
Blood clot in a deep vein	Sometimes (5–29%)
Low blood cell count	Sometimes (5–29%)
Low blood neutrophil count	Sometimes (5–29%)
Thromboembolism	Sometimes (5–29%)

Laboratory abnormality

Trait	How often it is seen
Elevated blood homocystine	Always
Decreased plasma methionine	Often (30–79%)
Decreased circulating methylcobalamin concentration	Not recorded
Decreased methionine synthase activity	Not recorded
High urine homocystine levels	Not recorded
Laboratory abnormality	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Low muscle tone	Often (30–79%)
Spasticity and rigidity of muscles	Often (30–79%)
Abnormality of the skeletal system	Sometimes (5–29%)
Osteoporosis	Sometimes (5–29%)
Scoliosis	Sometimes (5–29%)

Abnormality of the eye

Trait	How often it is seen
Abnormality of the eye	Often (30–79%)
Involuntary, rapid, rhythmic eye movements	Often (30–79%)
Blindness	Sometimes (5–29%)
Visual impairment	Sometimes (5–29%)

Abnormality of limbs

Trait	How often it is seen
Curvature of digit	Sometimes (5–29%)
Lower limb hypertonia	Sometimes (5–29%)
Webbed fingers or toes	Sometimes (5–29%)

Abnormality of the digestive system

Trait	How often it is seen
Feeding difficulties	Often (30–79%)
Vomiting	Often (30–79%)
Abnormality of the liver	Sometimes (5–29%)

Growth abnormality

Trait	How often it is seen
Faltering weight	Always
Growth delay as children	Often (30–79%)
Prenatal growth deficiency	Often (30–79%)

Abnormality of the cardiovascular system

Trait	How often it is seen
Abnormality of the cardiovascular system	Sometimes (5–29%)
High blood pressure	Sometimes (5–29%)

Abnormality of the genitourinary system

Trait	How often it is seen
Glomerulopathy	Sometimes (5–29%)
Hemolytic-uremic syndrome	Sometimes (5–29%)

Abnormality of head or neck

Trait	How often it is seen
Abnormally small head	Often (30–79%)

Abnormality of the ear

Trait	How often it is seen
Hearing impairment	Sometimes (5–29%)

How often is among people with one of the gene's conditions, the most often across them, as the Human Phenotype Ontology records it. These pages describe traits and the research behind them; they are not a diagnosis, and a doctor or genetic counsellor is the person to ask about symptoms.

Where this comes from

The Human Phenotype Ontology, release 2026-09-01: the traits linked to MTRR and how often each is seen. Find out more at hpo.jax.org.

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