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Multiple Epiphyseal Dysplasia (MED)
Sunday, 14 August 2005
Sunday, 14 August 2005

What

Multiple epiphyseal dysplasia (MED) encompasses a spectrum of skeletal disorders, most of which are inherited in an autosomal dominant form. However, there is also an autosomal recessive form. The disorder affects the growing ends of bones. Bones usually elongate by a process that involves the deposition of cartilage at the ends of the bones called ossification. This cartilage then mineralizes and hardens to become bone. In MED, this process is defective.

Who

Recent studies estimate the prevalence of the dominant form of MED to be 1 in 10,000 births. However, some have suggested that this is an underestimate since MED is not typically diagnosed at birth. Exact prevalence data is not available for the recessive form of MED.

Signs and Symptoms

Children with dominant MED experience joint pain and fatigue after exercising. Their x-rays show small and irregular ossifications centers, most apparent in the hips and knees. A waddling gait may develop. The spine is normal but may have a few irregularities. By adulthood, people with MED are of short stature or in the low range of normal and have short limbs relative to their trunk. Frequently, movement becomes limited at the major joints, especially at the elbows. However, loose knee and finger joints can occur. Signs of osteoarthritis usually begin in early adulthood. Children with recessive MED also experience joint pain, particularly of the hips and knees, but they also commonly have deformities of the hands, feet, knees, and/or vertebral column (like scoliosis). Approximately 50% of affected children have abnormal findings at birth (i.e. club foot, cleft palate, inward curving fingers due to underdeveloped bones, or rarely, ear swelling). Height is within the normal range prior to puberty. As adults, people with MED are only slightly more diminished in stature but still within the normal range. Functional disabilities of the joints are mild or absent.

Possible Causes

Approximately 50% of the dominant form of MED is caused by a mutation in one of five genes. These genes code for structural molecules of the cartilage that will turn into bone. Mutations in these genes result in abnormal structural molecules and the cartilage is defective and does not ossify (harden) properly. For the other 50% of patients, a genetic mutation or defect has not yet been identified. The recessive form of MED is due to a mutation in the SLC26A2 gene. This gene encodes for a protein called sulfate transporter. This transporter normally transports sulfate into the chondrocytes and fibroblasts (cells that are involved in bone formation). The sulfate is used in making the proteoglycans that form collagen. This collagen is deposited at the ends of bones and hardens. A mutation in the gene results in an abnormal sulfate transporter that does not allow sulfate to enter the cells. Without the sulfate, proteoglycans are not properly deposited at the ossification centers and the bone does not form properly. Different mutations along this gene are associated with varying degrees of severity of the disease symptoms.

Diagnosis

Diagnosis of the dominant form of MED is accomplished by considering clinical symptoms and from bone abnormalities found on x-ray. The x-rays of bones show abnormalities at the ossification centers in children with MED. The recessive form of MED is also diagnosed using the clinical symptoms and abnormalities found on x-ray. On x-ray the tubular bones look flat at their ends and evidence of early arthritis can be seen. The fingers are mildly shorter than normal and the patella (kneecap) has two ossification centers forming two layers. A genetic test to find the mutation in the SLC26A2 gene can be used for diagnosis.

Treatment

Medications and physiotherapy are utilized to alleviate the joint pain, which may be difficult to control. Orthopedic procedures may be helpful at slowing the progression of symptoms. It is recommended that people with MED avoid high impact exercise that strains the joints and maintain a healthy weight, avoiding obesity. Joint replacement may be necessary in early adulthood when osteoarthritis becomes severe in those with the dominant form of MED.

Prognosis

Children with MED live to adulthood. Adults with the dominant form frequently develop incapacitating osteoarthritis, and joint replacement may be required.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

WebMDHealth
The WebMD page contains a very brief and basic explanation of MED. However, it does list additional resources for information and support.

Cedars-Sinai
This link is to the Cedars-Sinai International Skeletal Dysplasia Registry. People can sign up to be in studies or get more information on dysplasia. This site also has a variety of links to other organizations and groups.

Little People of America
This is the site for the Little People of America organization. It is a place where people with bone disorders resulting in small stature can find informational resources and social support.

Google Search for Multiple Epiphyseal Dysplasia (MED)

References and Sources

www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15503005&query_hl=15 www.geneclinics.org/servlet/access?id=8888891&key=BZJV5RBw60dpZ&gry=INSERTGRY&fcn=y&fw=SkPm&filename=/profiles/edm-ad/index.html