3MC syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

3MC syndrome is a disorder characterized by unusual facial features and problems affecting other tissues and organs.

The distinctive facial features of people with 3MC syndrome include widely spaced eyes (hypertelorism), a narrowing of the eye opening (blepharophimosis), droopy eyelids (ptosis), highly arched eyebrows, and an opening in the upper lip (cleft lip) with an opening in the roof of the mouth (cleft palate).

Other common features of 3MC syndrome include developmental delay, intellectual disability, hearing loss, and slow growth after birth resulting in short stature. Less often, individuals with 3MC syndrome can have abnormal fusion of certain bones in the skull (craniosynostosis) or forearm (radioulnar synostosis); an outgrowth of the tailbone (caudal appendage); a soft out-pouching around the belly-button (an umbilical hernia); and abnormalities of the kidneys, bladder, or genitals.

3MC syndrome encompasses four disorders that were formerly considered to be separate: Mingarelli, Malpeuch, Michels, and Carnevale syndromes. Researchers now generally consider these disorders to be part of the same condition, which is called 3MC based on the initials of the older condition names.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

3MC syndrome is caused by mutations in the COLEC10, COLEC11, or MASP1 gene. These genes provide instructions for making proteins that are involved in a series of steps called the lectin complement pathway. This pathway is thought to help direct the movement (migration) of cells during development before birth to form the organs and systems of the body. The lectin complement pathway appears to be particularly important in directing the migration of neural crest cells. These cells give rise to various tissues including many tissues in the face and skull, the glands that produce hormones (endocrine glands), and portions of the nervous system. After birth, the lectin complement pathway is involved in the immune system.

The COLEC10, COLEC11, and MASP1 gene mutations that cause 3MC syndrome impair or eliminate the function of the corresponding proteins, resulting in faulty control of cell migration in early development. Impaired cell migration disrupts the normal growth and development of several tissues and organs, which leads to the various abnormalities that occur in this disorder. Researchers suggest that similar pathways in the immune system can compensate for problems in the lectin complement pathway, which explains why immune system abnormalities are not part of 3MC syndrome.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

3MC syndrome is a rare disorder; its prevalence is unknown.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Epicanthus inversus · Very frequent (99-80%)

A fold of skin starting at or just below the medial aspect of the lower lid and arching upward to cover, extend in front of and lateral to the medial canthus.

Hearing impairment · Very frequent (99-80%)

A decreased magnitude of the sensory perception of sound.

Highly arched eyebrow · Very frequent (99-80%)

Increased height of the central portion of the eyebrow, forming a crescent, semicircular, or inverted U shape.

Limited pronation/supination of forearm · Very frequent (99-80%)

A limitation of the ability to place the forearm in a position such that the palm faces anteriorly (supination) and to place the forearm in a position such that the palm faces posteriorly (pronation).

Ptosis · Very frequent (99-80%)

The upper eyelid margin is positioned 3 mm or more lower than usual and covers the superior portion of the iris (objective); or, the upper lid margin obscures at least part of the pupil (subjective).

Radioulnar synostosis · Very frequent (99-80%)

An abnormal osseous union (fusion) between the radius and the ulna.

Abnormal anterior chamber morphology · Frequent (79-30%)

Abnormality of the anterior chamber, which is the space in the eye that is behind the cornea and in front of the iris.

Bilateral cryptorchidism · Frequent (79-30%)

Absence of both testes from the scrotum owing to failure of the testis or testes to descend through the inguinal canal to the scrotum.

Blepharophimosis · Frequent (79-30%)

A fixed reduction in the vertical distance between the upper and lower eyelids with short palpebral fissures.

Craniosynostosis · Frequent (79-30%)

Craniosynostosis refers to the premature closure of the cranial sutures. Primary craniosynostosis refers to the closure of one or more sutures due to abnormalities in skull development, and secondary craniosynostosis results from failure of brain growth.

Diastasis recti · Frequent (79-30%)

A separation of the rectus abdominis muscle into right and left halves (which are normally joined at the midline at the linea alba).

Downslanted palpebral fissures · Frequent (79-30%)

The palpebral fissure inclination is more than two standard deviations below the mean.

Downturned corners of mouth · Frequent (79-30%)

A morphological abnormality of the mouth in which the angle of the mouth is downturned. The oral commissures are positioned inferior to the midline labial fissure.

Hyperlordosis · Frequent (79-30%)

Abnormally increased curvature (anterior concavity) of the lumbar or cervical spine.

Other findings in the same source

From: Orphanet

Additional reported features include Hypertelorism (Frequent (79-30%)); Intellectual disability (Frequent (79-30%)); Orofacial cleft (Frequent (79-30%)); Postnatal growth retardation (Frequent (79-30%)); Scoliosis (Frequent (79-30%)); Spina bifida occulta (Frequent (79-30%)); Supernumerary nipple (Frequent (79-30%)); Telecanthus (Frequent (79-30%)); Large fleshy ears (Frequent (79-30%)); Abnormal pinna morphology (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing 3MC syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for 3MC syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.