Traits

Traits linked to MMACHC

metabolism of cobalamin associated C

The Human Phenotype Ontology links 105 traits to MMACHC, by body system: features seen in people with one of the gene's rare conditions.

MMACHC

Abnormality of the nervous system

Trait	How often it is seen
Intellectual disability	Very often (80–99%)
Abnormal speech pattern	Sometimes (5–29%)
Abnormality of the nervous system	Sometimes (5–29%)
Ataxia	Sometimes (5–29%)
Behavioral abnormality	Sometimes (5–29%)
Degeneration of cerebrum	Sometimes (5–29%)
Degeneration of the spinal cord	Sometimes (5–29%)
Encephalopathy	Sometimes (5–29%)
Epilepsy	Sometimes (5–29%)
Hallucinations of sound	Sometimes (5–29%)
Impaired executive functioning	Sometimes (5–29%)
Infantile spasms	Sometimes (5–29%)
Lethargy	Sometimes (5–29%)
Leukoencephalopathy	Sometimes (5–29%)
Memory impairment	Sometimes (5–29%)
Mental deterioration	Sometimes (5–29%)
Neurodevelopmental delay	Sometimes (5–29%)
Peripheral demyelination	Sometimes (5–29%)
Periventricular white matter hyperintensities	Sometimes (5–29%)
Personality changes	Sometimes (5–29%)
Poor fine motor coordination	Sometimes (5–29%)
Abnormal shape of brain	Rarely (1–4%)
Delirium	Rarely (1–4%)
Dementia	Rarely (1–4%)
Loss of developmental milestones	Rarely (1–4%)
Psychosis	Rarely (1–4%)
Severe demyelination of the white matter	Rarely (1–4%)
Too much cerebrospinal fluid in the brain	Rarely (1–4%)
Abnormality of extrapyramidal motor function	Not recorded
Confusion	Not recorded
Decrease in size of the outer layer of the brain due to loss of brain cells	Not recorded
Global developmental delay	Not recorded
Tremor	Not recorded

Laboratory abnormality

Trait	How often it is seen
Decreased methionine synthase activity	Always
Decreased methylmalonyl-CoA mutase activity	Always
Elevated blood homocystine	Very often (80–99%)
Elevated circulating palmitoleylcarnitine concentration	Very often (80–99%)
Methylmalonic acidemia	Very often (80–99%)
Methylmalonic aciduria	Very often (80–99%)
Decreased plasma methionine	Often (30–79%)
Dehydration	Sometimes (5–29%)
High blood ammonia levels	Sometimes (5–29%)
Hydrops fetalis	Sometimes (5–29%)
Hypothermia	Sometimes (5–29%)
Ketonuria	Sometimes (5–29%)
Low blood sugar	Sometimes (5–29%)
Metabolic acidosis	Rarely (1–4%)
Blood in urine	Not recorded
Decreased circulating adenosylcobalamin concentration	Not recorded
Decreased circulating methylcobalamin concentration	Not recorded
High blood cystathionine levels	Not recorded
High urine cystathionine levels	Not recorded
High urine homocystine levels	Not recorded
High urine protein levels	Not recorded

Abnormality of the cardiovascular system

Trait	How often it is seen
Elevated heart rate	Often (30–79%)
Heart stops beating	Often (30–79%)
Increased blood pressure in blood vessels of lungs	Often (30–79%)
Low blood pressure	Often (30–79%)
Slow heartbeats	Often (30–79%)
Abnormality of the heart	Sometimes (5–29%)
Stretched and thinned heart muscle	Sometimes (5–29%)
Blood clot in artery of lung	Rarely (1–4%)
Stroke	Rarely (1–4%)

Abnormality of the eye

Trait	How often it is seen
Abnormal macular pigmentation	Often (30–79%)
Involuntary, rapid, rhythmic eye movements	Often (30–79%)
Macular pseudocoloboma	Often (30–79%)
Optic atrophy	Often (30–79%)
Pigmentary retinopathy	Often (30–79%)
Retina degeneration	Often (30–79%)
Visual impairment	Often (30–79%)
Decreased clarity of vision	Not recorded

Abnormality of head or neck

Trait	How often it is seen
Abnormally small head	Often (30–79%)
Inflammation of the mouth	Often (30–79%)
Inflammation of the tongue	Often (30–79%)
Abnormal facial shape	Rarely (1–4%)
High forehead	Rarely (1–4%)
Long face	Rarely (1–4%)
Smooth philtrum	Rarely (1–4%)

Abnormality of blood and blood-forming tissues

Trait	How often it is seen
Megaloblastic anemia	Very often (80–99%)
Low platelet count	Often (30–79%)
Blood clot in a deep vein	Sometimes (5–29%)
Low blood neutrophil count	Sometimes (5–29%)
Subdural hemorrhage	Sometimes (5–29%)
Thromboembolism	Sometimes (5–29%)

Abnormality of the digestive system

Trait	How often it is seen
Enlarged liver	Often (30–79%)
Feeding difficulties	Often (30–79%)
Vomiting	Often (30–79%)
Jaundice	Sometimes (5–29%)
Feeding difficulties in infancy	Not recorded

Abnormality of the genitourinary system

Trait	How often it is seen
Acute kidney injury	Often (30–79%)
Glomerulopathy	Often (30–79%)
Renal failure	Sometimes (5–29%)
Hemolytic-uremic syndrome	Rarely (1–4%)
Kidney damage	Not recorded

Growth abnormality

Trait	How often it is seen
Faltering weight	Often (30–79%)
Growth delay	Often (30–79%)
Small for gestational age	Often (30–79%)
Prenatal growth deficiency	Sometimes (5–29%)

Abnormality of the musculoskeletal system

Trait	How often it is seen
Low muscle tone in trunk	Often (30–79%)
Low muscle tone	Sometimes (5–29%)
Generalized decreased muscle tone	Not recorded

Abnormality of the ear

Trait	How often it is seen
Low-set ears	Rarely (1–4%)
Large ears	Not recorded

Abnormality of the integument

Trait	How often it is seen
Paleness	Often (30–79%)

Abnormality of the respiratory system

Trait	How often it is seen
Breathing difficulties	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 MMACHC and how often each is seen. Find out more at hpo.jax.org.

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