Traits

Traits linked to MMADHC

metabolism of cobalamin associated D

The Human Phenotype Ontology links 59 traits to MMADHC, 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
Abnormal gait	Always
Absent speech development	Always
Aggressive behavior	Always
Brisk reflexes	Always
Cerebellar vermis hypoplasia	Always
Coma	Always
Degeneration of cerebellum	Always
Degeneration of cerebrum	Always
Delayed CNS myelination	Always
Dystonia	Always
Encephalopathy	Always
Epilepsy	Always
Global developmental delay	Always
Intellectual disability, mild	Always
Intellectual disability, severe	Always
Interictal EEG abnormality	Always
IQ between 34 and 49	Always
Lack of coordination of movement	Always
More active than typical	Always
Poor eye contact	Always
Psychosis	Always
Spastic ataxia	Always
Abnormality of movement	Very often (80–99%)
Behavioral abnormality	Very often (80–99%)
Intellectual disability	Very often (80–99%)
Lethargy	Very often (80–99%)
Decrease in size of the outer layer of the brain due to loss of brain cells	Not recorded

Laboratory abnormality

Trait	How often it is seen
Decreased plasma methionine	Always
Dehydration	Always
Elevated blood homocystine	Always
High blood ammonia levels	Always
High urine homocystine levels	Always
Increased circulating folate concentration	Always
Ketoacidosis	Always
Methylmalonic aciduria	Always
Decreased circulating adenosylcobalamin concentration	Not recorded
Decreased circulating methylcobalamin concentration	Not recorded
Decreased methionine synthase activity	Not recorded
Decreased methylmalonyl-CoA mutase activity	Not recorded
Methylmalonic acidemia	Not recorded

Abnormality of blood and blood-forming tissues

Trait	How often it is seen
Bleeding within the skull	Always
Decreased blood leukocyte number	Always
Increased mean corpuscular volume	Always
Low platelet count	Always
Megaloblastic anemia	Always
Megaloblastic bone marrow	Very often (80–99%)

Abnormality of the digestive system

Trait	How often it is seen
Feeding difficulties	Always
Necrotizing enterocolitis	Always
Anorexia	Very often (80–99%)

Abnormality of the eye

Trait	How often it is seen
Horizontal nystagmus	Always
Involuntary, rapid, rhythmic eye movements	Always

Abnormality of the musculoskeletal system

Trait	How often it is seen
Low muscle tone	Always
Generalized decreased muscle tone	Not recorded

Abnormality of limbs

Trait	How often it is seen
Absent ankle reflexes	Always

Abnormality of prenatal development or birth

Trait	How often it is seen
Premature birth	Always

Abnormality of the integument

Trait	How often it is seen
Paleness	Very often (80–99%)

Abnormality of the respiratory system

Trait	How often it is seen
Neonatal respiratory distress	Always

Constitutional symptom

Trait	How often it is seen
Fatigue	Very often (80–99%)

Growth abnormality

Trait	How often it is seen
Faltering weight	Very often (80–99%)

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 MMADHC and how often each is seen. Find out more at hpo.jax.org.

One test. A lifetime of answers.

From $449Free shipping · Results in 6–8 weeks

Get my Genome Test