Traits

Traits linked to MASP1

MBL associated serine protease 1

The Human Phenotype Ontology links 58 traits to MASP1, by body system: features seen in people with one of the gene's rare conditions.

Abnormality of head or neck

Trait	How often it is seen
Downward slanting of the opening between the eyelids	Always
Highly arched eyebrow	Always
Epicanthus inversus	Very often (80–99%)
Cleft lip	Often (30–79%)
Cleft of the mouth	Often (30–79%)
Cleft palate	Often (30–79%)
Corners of eye widely separated	Often (30–79%)
Deformity of the skull	Often (30–79%)
Downturned corners of mouth	Often (30–79%)
Monobrow	Often (30–79%)
Narrow opening between the eyelids	Often (30–79%)
Abnormal of nasal shape	Sometimes (5–29%)
Skull asymmetry	Sometimes (5–29%)
Abnormally small head	Not recorded
Coronal craniosynostosis	Not recorded
Dental crowding	Not recorded
Flattened bony protrusion above eyes	Not recorded
Lambdoidal craniosynostosis	Not recorded
Small dilated blood vessels near membrane covering front of eye and eyelids	Not recorded
Wider-than-typical soft spot of skull	Not recorded

Abnormality of limbs

Trait	How often it is seen
Fused forearm bones	Very often (80–99%)
Limited pronation/supination of forearm	Very often (80–99%)
Hip dislocation	Sometimes (5–29%)
Broad foot	Not recorded
Curvature of little finger	Not recorded
Short 5th finger	Not recorded
Short foot	Not recorded
Single interphalangeal crease of fifth finger	Not recorded

Abnormality of the ear

Trait	How often it is seen
Hearing impairment	Very often (80–99%)
Conductive deafness	Often (30–79%)
Large fleshy ears	Often (30–79%)
Abnormally shaped ears	Sometimes (5–29%)
Low-set ears	Sometimes (5–29%)

Abnormality of the eye

Trait	How often it is seen
Drooping upper eyelid	Always
Abnormal anterior chamber morphology	Often (30–79%)
Wide-set eyes	Often (30–79%)
Abnormality of eye movement	Not recorded
Glaucoma	Not recorded

Abnormality of the digestive system

Trait	How often it is seen
Periumbilical depression	Always
Gap between large left and right abdominal muscles	Often (30–79%)
Umbilical hernia	Sometimes (5–29%)
Abnormality of the abdominal wall	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Human tail	Often (30–79%)
Prominent swayback	Often (30–79%)
Scoliosis	Often (30–79%)
Prominent tailbone	Sometimes (5–29%)

Abnormality of the cardiovascular system

Trait	How often it is seen
An opening in the wall separating the top two chambers of the heart	Not recorded
Hole in heart wall separating two lower heart chambers	Not recorded
Patent ductus arteriosus	Not recorded

Abnormality of the nervous system

Trait	How often it is seen
Intellectual disability, mild	Always
Intellectual disability	Often (30–79%)
Spina bifida occulta	Often (30–79%)

Abnormality of the genitourinary system

Trait	How often it is seen
Bilateral cryptorchidism	Often (30–79%)
Hydronephrosis	Not recorded

Growth abnormality

Trait	How often it is seen
Growth delay as children	Often (30–79%)
Growth delay	Not recorded

Abnormality of the breast

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

Abnormality of the integument

Trait	How often it is seen
Spinal dimple	Not recorded

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 MASP1 and how often each is seen. Find out more at hpo.jax.org.

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