Craniometaphyseal dysplasia

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Craniometaphyseal dysplasia is a rare condition characterized by thickening (overgrowth) of bones in the skull (cranium) and abnormalities in a region at the end of long bones known as the metaphysis. The abnormal bone growth continues throughout life. Except in the most severe cases, the lifespan of people with craniometaphyseal dysplasia is normal.

Bone overgrowth in the head causes many of the signs and symptoms of craniometaphyseal dysplasia. Affected individuals typically have distinctive facial features such as a wide nasal bridge, a prominent forehead, wide-set eyes (hypertelorism), and a prominent jaw. Excess bone formation in the jaw can delay teething (dentition) or result in absent (non-erupting) teeth. Infants with craniometaphyseal dysplasia may have breathing or feeding problems caused by narrow nasal passages. In severe cases, abnormal bone growth can pinch (compress) the nerves that extend from the brain to various areas of the head and neck (cranial nerves). Compression of the cranial nerves can lead to paralyzed facial muscles (facial nerve palsy), blindness, or deafness.

The x-rays of individuals with craniometaphyseal dysplasia show unusually shaped long bones, particularly long bones in the legs. The ends of these bones are wider and appear less dense than usual in people with this condition.

There are two types of craniometaphyseal dysplasia, which are distinguished by their pattern of inheritance and genetic cause. They are known as the autosomal dominant and autosomal recessive types.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the ANKH gene cause autosomal dominant craniometaphyseal dysplasia. The ANKH gene provides instructions for making a protein that plays a role in the development and function of cells that build bones (osteoblasts) and cells that break down bone (osteoclasts). Osteoclasts are involved in bone remodeling, a normal process in which old bone is removed and new bone is created to replace it. In addition, the ANKH protein transports a molecule called pyrophosphate out of cells. The pyrophosphate found outside of cells (extracellular pyrophosphate) helps control bone formation by preventing mineralization, the process by which minerals such as calcium and phosphorus are deposited in developing bones. The ANKH protein may have other, unknown functions.

Mutations in the ANKH gene that cause autosomal dominant craniometaphyseal dysplasia impair the maturation (differentiation) of osteoclasts, which likely disrupts bone remodeling. Reduced breakdown of bone tissue can contribute to the bone thickening characteristic of craniometaphyseal dysplasia. ANKH gene mutations may also reduce the protein's ability to transport pyrophosphate out of cells. A shortage of extracellular pyrophosphate can increase bone mineralization, which may also contribute to the bone abnormalities.

A mutation in the GJA1 gene causes some cases of autosomal recessive craniometaphyseal dysplasia. This gene provides instructions for making a protein called connexin 43, which is involved in the development of many tissues in the body, including bone. The protein may be involved in bone remodeling. It is unclear how a mutation in the GJA1 gene leads to the particular bone abnormalities of craniometaphyseal dysplasia.

The genetic cause of many cases of autosomal recessive craniometaphyseal dysplasia is unknown. It is likely that other, unidentified genes are involved in this form of the disorder.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

When caused by mutations in the ANKH gene, craniometaphyseal dysplasia follows an autosomal dominant pattern, which means one altered copy of the ANKH gene in each cell is sufficient to cause the disorder. Individuals with autosomal dominant craniometaphyseal dysplasia typically have one parent who also has the condition. Less often, cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

When caused by mutations in the GJA1 gene, craniometaphyseal dysplasia has an autosomal recessive inheritance pattern, which means both copies of the GJA1 gene in each cell are altered. 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 disorder.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Craniometaphyseal dysplasia is a very rare disorder; its incidence 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.

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.

Craniofacial hyperostosis · Very frequent (99-80%)

Excessive growth of the craniofacial bones.

Depressed nasal bridge · Very frequent (99-80%)

Posterior positioning of the nasal root in relation to the overall facial profile for age.

Hypertelorism · Very frequent (99-80%)

Interpupillary distance more than 2 SD above the mean (alternatively, the appearance of an increased interpupillary distance or widely spaced eyes).

Osteopetrosis · Very frequent (99-80%)

Abnormally increased formation of dense trabecular bone tissue. Despite the increased density of bone tissue, osteopetrotic bones tend to be more fracture-prone than normal.

Wide nasal bridge · Very frequent (99-80%)

Increased breadth of the nasal bridge (and with it, the nasal root).

Skeletal dysplasia · Frequent (79-30%)

A general term describing features characterized by abnormal development of bones and connective tissues.

Telecanthus · Frequent (79-30%)

Distance between the inner canthi more than two standard deviations above the mean (objective); or, apparently increased distance between the inner canthi.

Other findings in the same source

From: Orphanet

Additional reported features include Abnormal cranial nerve morphology (Occasional (29-5%)); Conductive hearing impairment (Occasional (29-5%)); Facial palsy (Occasional (29-5%)); Sensorineural hearing impairment (Occasional (29-5%)); Visual impairment (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 Craniometaphyseal dysplasia 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 Craniometaphyseal dysplasia. 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.