3-M syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

3-M syndrome is a disorder that causes skeletal abnormalities including short stature (dwarfism) and unusual facial features. The name of this condition comes from the initials of three researchers who first identified it: Miller, McKusick, and Malvaux.

Individuals with 3-M syndrome grow extremely slowly before birth, and this slow growth continues throughout childhood and adolescence. They have low birth weight and length and remain much smaller than others in their family, growing to an adult height of approximately 4 feet to 4 feet 6 inches (120 centimeters to 130 centimeters). In some affected individuals, the head is normal-sized but looks disproportionately large in comparison with the body. In other people with this disorder, the head has an unusually long and narrow shape (dolichocephaly). Intelligence is unaffected by 3-M syndrome, and life expectancy is generally normal.

In addition to short stature, people with 3-M syndrome have a triangle-shaped face with a broad, prominent forehead (frontal bossing) and a pointed chin; the middle of the face is less prominent (hypoplastic midface). Other common features include large ears, full eyebrows, an upturned nose with a fleshy tip, a long area between the nose and mouth (philtrum), a prominent mouth, and full lips.

Other skeletal abnormalities that often occur in this disorder include a short, broad neck and chest; prominent shoulder blades; and shoulders that slope less than usual (square shoulders). Affected individuals may have abnormal spinal curvature such as a rounded upper back that also curves to the side (kyphoscoliosis) or exaggerated curvature of the lower back (hyperlordosis). People with 3-M syndrome can also have unusual curving of the fingers (clinodactyly), short fifth (pinky) fingers, prominent heels, and loose joints. Additional skeletal abnormalities, such as unusually slender long bones in the arms and legs; tall, narrow spinal bones (vertebrae); or slightly delayed bone age may be apparent in x-ray images.

A variant of 3-M syndrome called Yakut short stature syndrome has been identified in the isolated Yakut population in the Russian province of Siberia. In addition to having most of the physical features characteristic of 3-M syndrome, people with this form of the disorder are often born with breathing problems that can be life-threatening in infancy.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the CUL7 gene cause 3-M syndrome in more than three-quarters of affected individuals, including those in the Yakut population. Mutations in the OBSL1 gene cause about 16 percent of cases of this disorder. Mutations in other genes, some of which have not been identified, account for the remaining cases.

The CUL7 gene provides instructions for making a protein called cullin-7. The cullin-7 protein plays a role in the cell machinery that breaks down (degrades) unwanted proteins, called the ubiquitin-proteasome system. Specifically, cullin-7 helps assemble a complex called an E3 ubiquitin ligase, which tags the unneeded proteins for degradation. The protein produced from the OBSL1 gene is thought to help maintain normal levels of cullin-7.

The ubiquitin-proteasome system helps regulate the level of proteins involved in several critical cell activities such as the timing of cell division and growth. In particular, the proteins produced from the genes associated with 3-M syndrome are thought to help regulate proteins involved in the body's response to growth hormones, although their specific role in this process is unknown.

Mutations in the CUL7 or OBSL1 gene prevent the cullin-7 protein from bringing together the components of the E3 ubiquitin ligase complex, interfering with the process of tagging unneeded proteins for degradation. The body's response to growth hormones may be impaired as a result. However, the specific relationship between CUL7 and OBSL1 gene mutations and the signs and symptoms of 3-M syndrome are unknown.

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

The prevalence of 3-M syndrome is unknown. About 100 individuals worldwide with this disorder have been described in the medical literature.

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.

Abnormal metaphysis morphology · Very frequent (99-80%)

An abnormality of one or more metaphysis, i.e., of the somewhat wider portion of a long bone that is adjacent to the epiphyseal growth plate and grows during childhood.

Anteverted nares · Very frequent (99-80%)

Anteriorly-facing nostrils viewed with the head in the Frankfurt horizontal and the eyes of the observer level with the eyes of the subject. This gives the appearance of an upturned nose (upturned nasal tip).

Broad forehead · Very frequent (99-80%)

Width of the forehead or distance between the frontotemporales is more than two standard deviations above the mean (objective); or apparently increased distance between the two sides of the forehead.

Bulbous nose · Very frequent (99-80%)

Increased volume and globular shape of the anteroinferior aspect of the nose.

Delayed skeletal maturation · Very frequent (99-80%)

A decreased rate of skeletal maturation. Delayed skeletal maturation can be diagnosed on the basis of an estimation of the bone age from radiographs of specific bones in the human body.

Everted lower lip vermilion · Very frequent (99-80%)

An abnormal configuration of the lower lip such that it is turned outward i.e., everted, with the Inner aspect of the lower lip vermilion (normally opposing the teeth) being visible in a frontal view.

Frontal bossing · Very frequent (99-80%)

Bilateral bulging of the lateral frontal bone prominences with relative sparing of the midline.

Hypoplastic ischia · Very frequent (99-80%)

Underdevelopment of the ischium, which forms the lower and back part of the hip bone.

Other findings in the same source

From: Orphanet

Additional reported features include Hypoplastic pelvis (Very frequent (99-80%)); Hypoplastic pubic bone (Very frequent (99-80%)); Increased vertebral height (Very frequent (99-80%)); Intrauterine growth retardation (Very frequent (99-80%)); Midface retrusion (Very frequent (99-80%)); Rocker bottom foot (Very frequent (99-80%)); Scapular winging (Very frequent (99-80%)); Short neck (Very frequent (99-80%)); Short stature (Very frequent (99-80%)); Slender long bone (Very frequent (99-80%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing 3-M syndrome is Orthopaedics, with a orthopaedic specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

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.

• What explains the change in pain, movement or function?
• Which activities need adjustment while the diagnosis is being clarified?
• What are the roles of rehabilitation, observation and surgery in this situation?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for 3-M 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.