Metatropic Dysplasia was initially described in 1966. It begins as a short-limbed dysplasia, and over time develops into a short trunk dysplasia. Due to this change in body proportions, the name “metatropic” is derived from the Greek word “metatropos,” meaning "changing form."
Metatropic dysplasia belongs to a family of dysplasias which include: Parastremmatic dysplasia; Spondylmetaphyseal dysplasia, Koslowski Type; Spondyloepiphyseal dysplasia, Maroteaux Type; and Brachyolmia.
Metatropic dysplasia is a rare disorder, and the exact incidence is not known.
Learn more about treatment options.
Metatropic dysplasia is caused by a mutation in the Transient Receptor Potential Cation Channel Subfamily V Member 4 (TRPV4) gene. The TRPV4 gene encodes a transmembrane calcium channel which plays an important role in cartilage, bone and neuromuscular function. In metatropic dysplasia, the TRPV4 channel is overactive.
Metatropic dysplasia has autosomal dominant inheritance.
Initially, individuals have shortened limbs with a relatively average-sized trunk (short-limbed dwarfism). As the child gets older and the condition progresses, kyphoscoliosis of the spine develops that decreases trunk height (short-trunk dwarfism). Apparent shortening of the limbs also occurs over time, due to progressive joint contractures.
The radiographic features of metatropic dysplasia include small, flat, diamond-shaped vertebral bodies in early infancy. Later, platyspondyly and anterior wedging of vertebral bodies are characteristic.
The pedicles are overfaced. The lateral border of the vertebral body appears outside the lateral edge of the pedicle.
The thorax is narrow and ribs are short, in both infancy and early childhood.
Metatropic dysplasia is diagnosed by its clinical and radiographic characteristic features. Genetic testing of the TRPV4 gene can be performed to confirm the diagnosis.
Atlantoaxial instability and cervical stenosis are very common in metatropic dysplasia. Flexion and extension X-rays of the neck should be performed at diagnosis and at periodic intervals thereafter. Further information can be obtained by means of an MRI scan, typically done with flexion and extension views as well. If cervical instability is progressive or symptomatic, surgical fusion with decompression may be necessary.
Kyphoscoliosis is commonly seen in early childhood. It is often severe and rapidly progressive. The spine should be imaged early and followed-up at regular intervals. Bracing may be of some benefit in younger children with smaller curves.
The timing of spinal decompression and fusion for scoliosis in metatropic dysplasia is dependent upon the severity of the curve, curve progression, age and risk of injury to the spinal cord. The status of the respiratory system may also dictate the timing of surgery, especially in the younger, more severely affected children
The limbs are short with significant joint contractures. Treatment is dictated by walking ability, amount of functional compromise and symptoms. Common problems include hip and knee flexion contractures and genu valgum. Some individuals can have ligamentous laxity.
In one study from our center, we found that 40% of our patients with metatropic dysplasia had a fracture, with 25% having two or more.
Respiratory difficulties result from a stiff, small and narrow rib cage as well as tracheal and bronchomalacia in some children. Prolonged breathing difficulties may warrant a tracheostomy and long-term ventilatory support. Other serious causes of respiratory issues are spinal cord compression and neuromuscular disease. Lung function tests and sleep studies are frequently used to diagnose breathing problems in skeletal dysplasias. Regular review by a pulmonologist is recommended.
Sensorineural hearing loss can occur in metatropic dysplasia, and routine hearing assessments are necessary.
For individuals with metatropic, any change in walking ability, endurance or breathing should have further assessment by a medical provider to rule out spinal cord compression. Specific neurological symptoms such as tingling or numbness in the arms or legs, weakness, shooting leg or arm pain, or problems controlling bladder/bowel function should be investigated further.
One should also watch out for progressive curvature of the spine.
When undergoing any surgical procedure, management of the airway by an anesthesiologist is very important, as difficult airway is common, especially if their cervical spine has been fused.
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