Metatropic dysplasia

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Metatropic dysplasia is a skeletal disorder characterized by short stature (dwarfism) with other skeletal abnormalities. The term "metatropic" is derived from the Greek word "metatropos," which means "changing patterns." This name reflects the fact that the skeletal abnormalities associated with the condition change over time.

Affected infants are born with a narrow chest and unusually short arms and legs with dumbbell-shaped long bones. Beginning in early childhood, people with this condition develop abnormal side-to-side and front-to-back curvature of the spine (scoliosis and kyphosis, often called kyphoscoliosis when they occur together). The curvature worsens with time and tends to be resistant to treatment. Because of the severe kyphoscoliosis, affected individuals may ultimately have a very short torso in relation to the length of their arms and legs.

Some people with metatropic dysplasia are born with an elongated tailbone known as a coccygeal tail; it is made of a tough but flexible tissue called cartilage. The coccygeal tail usually shrinks over time. Other skeletal problems associated with metatropic dysplasia include flattened bones of the spine (platyspondyly); excessive movement of spinal bones in the neck that can damage the spinal cord; either a sunken chest (pectus excavatum) or a protruding chest (pectus carinatum); and joint deformities called contractures that restrict the movement of joints in the shoulders, elbows, hips, and knees. Beginning early in life, affected individuals can also develop a degenerative form of arthritis that causes joint pain and further restricts movement.

The signs and symptoms of metatropic dysplasia can vary from relatively mild to life-threatening. In the most severe cases, the narrow chest and spinal abnormalities prevent the lungs from expanding fully, which restricts breathing. Researchers formerly recognized several distinct forms of metatropic dysplasia based on the severity of the condition's features. The forms included a mild type, a classic type, and a lethal type. However, all of these forms are now considered to be part of a single condition with a spectrum of overlapping signs and symptoms.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Metatropic dysplasia is caused by mutations in the TRPV4 gene, which provides instructions for making a protein that acts as a calcium channel. The TRPV4 channel transports positively charged calcium atoms (calcium ions) across cell membranes and into cells. The channel is found in many types of cells, but little is known about its function. Studies suggest that it plays a role in the normal development of cartilage and bone. This role would help explain why TRPV4 gene mutations cause the skeletal abnormalities characteristic of metatropic dysplasia. Mutations in the TRPV4 gene appear to overactivate the channel, increasing the flow of calcium ions into cells. However, it remains unclear how changes in the activity of the calcium channel lead to the specific features of the condition.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Metatropic dysplasia is considered an autosomal dominant disorder because one mutated copy of the TRPV4 gene in each cell is sufficient to cause the condition. Most cases of metatropic dysplasia are caused by new mutations in the gene and occur in people with no history of the disorder in their family. In a few reported cases, an affected person has inherited the condition from an affected parent.

In the past, it was thought that the lethal type of metatropic dysplasia had an autosomal recessive pattern of inheritance, in which both copies of the gene in each cell have mutations. However, more recent research has confirmed that all metatropic dysplasia has an autosomal dominant pattern of inheritance.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Metatropic dysplasia is a rare disease; its exact prevalence is unknown. More than 80 affected individuals have been reported in the scientific 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 cortical bone morphology · Very frequent (99-80%)

An abnormality of compact bone (also known as cortical bone), which forms the dense surface of bones.

Abnormal enchondral ossification · Very frequent (99-80%)

An abnormality of the process of endochondral ossification, which is a type of replacement ossification in which bone tissue replaces cartilage.

Abnormal form of the vertebral bodies · Very frequent (99-80%)

Abnormal form of vertebral body, which is the central cylindrical portion of the vertebra that together with other structures such as the vertebral arch, pedicles, laminae, spinous process, transverse processes, and articular facets makes up a vertebra.

Abnormal intervertebral disk morphology · Very frequent (99-80%)

Any structural abnormality of the intervertebral disk.

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.

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

An anomaly of the rib.

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

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

Halberd-shaped pelvis · Very frequent (99-80%)

An anomalous radiographic appearance of the developing pelvis, in which the greater ischiadic noth (incisura ischiadica major) is shallow and the pelvis takes on the appearance said to resemble a halberd (a weapon especially of the 15th and 16th centuries consisting typically of a battle-ax and pike mounted on a handle).

Other findings in the same source

From: Orphanet

Additional reported features include High forehead (Very frequent (99-80%)); Joint stiffness (Very frequent (99-80%)); Kyphosis (Very frequent (99-80%)); Long thorax (Very frequent (99-80%)); Micromelia (Very frequent (99-80%)); Narrow chest (Very frequent (99-80%)); Rough bone trabeculation (Very frequent (99-80%)); Scoliosis (Very frequent (99-80%)); Severe short stature (Very frequent (99-80%)); Skeletal dysplasia (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 Metatropic 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

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

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.

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.