sulfate transporter-related osteochondrodysplasia
What is Sulfate Transporter-Related Osteochondrodysplasia?
Sulfate transporter-related osteochondrodysplasias are a group of inherited diseases caused by mutations in a gene important in cartilage and bone formation, called SLC26A2. These diseases include: achondrogenesis type 1B, diastrophic dysplasia, and recessive multiple epiphyseal dysplasia.
Achondrogenesis type 1B
Achondrogenesis type 1B (ACG1B) is a severe skeletal disease that is fatal either before or shortly after birth.
Infants born with the disease have extremely short arms, legs, fingers, and toes. The fingers and toes may be rotated inward. Infants with the disease also tend to have flat faces, protruding abdomens, narrow chests, and short necks that show thickening of the soft tissue. Many are born with hernias.
Fetuses with ACG1B are often in the breech position, “upside-down” with their feet toward the birth canal. Mothers of fetuses with ACG1B are prone to certain other pregnancy complications.
Diastrophic dysplasia, also called diastrophic dwarfism, causes a person to be extremely small in stature. It also causes joint pain, difficulty with movement, and bone and joint abnormalities.
People with diastrophic dysplasia have very short arms and legs, although their skulls are often normally sized. They are often born with bone deformities such as club foot, cleft palate, a curved spine, and "hitchhiker thumbs" which are bent back. The outside of the ears are often swollen at birth and this can result in abnormal-looking ears later in life. People with the disease also tend to have small chests and protruding abdomens. The disease can cause breathing problems in infants, particularly due to the small size of the ribcage.
Those with the disease develop joint pain from an early age and have difficulty moving their joints. These symptoms worsen with age. Walking may become difficult for people with the disease. Adult height of people with diastrophic dysplasia often ranges from 3.2 feet to 4.6 feet.
Diastrophic dysplasia does not typically affect intelligence or mental function.
Recessive multiple epiphyseal dysplasia
Recessive multiple epiphyseal dysplasia (rMED) causes bone deformities and joint pain. Unlike people with related diseases, those with rMED typically reach normal height and live normal lifespans.
Half of people with rMED are born with an obvious bone abnormality such as cleft palate, club foot, or an inwardly-curved pinky finger. Some also have a mild curvature of the spine (scoliosis).
All people with the disease develop joint pain, often late in childhood. Pain is most common in the hips and knees but can also occur in the wrists, fingers, and elsewhere.
How common is Sulfate Transporter-Related Osteochondrodysplasia?
ACG1B is very rare, and its frequency is unknown. One particular mutation that causes the disease is most common in Finland, but other mutations are found globally.
Diastrophic dysplasia has been estimated to affect 1 in 100,000 people worldwide. It has been found in people of all ethnicities, but is most common in Finland.
Recessive multiple epiphyseal dysplasia is also rare, but researchers believe it may be more common than realized due to people with mild symptoms who go undiagnosed.
How is Sulfate Transporter-Related Osteochondrodysplasia treated?
There is no treatment for ACG1B. Infants with the disease can only be made as comfortable as possible.
For people with diastrophic dysplasia, the goal of treatment is to improve and maintain mobility while relieving pain. This can be done with a combination of muscle exercises, surgery, and the use of plaster casts to hold childrens' joints in place. In particular, surgery can be used to correct club foot, to reduce compression of the spinal cord, or to correct knee joints. Surgery may need to be repeated as bone deformities tend to re-form after surgery. It is important that people with diastrophic dysplasia do not become obese, as this puts harmful weight on their knee and ankle joints.
Recessive multiple epiphyseal dysplasia is usually treated through a combination of targeted muscle strengthening exercises and non-steroidal anti-inflammatory drugs (NSAIDs). People with the disease should avoid sports and activities that stress their joints. Obesity too can put strain on the joints. In some circumstances, surgery may be useful.
What is the prognosis for a person with Sulfate Transporter-Related Osteochondrodysplasia?
The prognosis for an infant with ACG1B is poor. They will die before or shortly after birth.
Infants with diastrophic dysplasia rarely face life-threatening breathing problems. Most people with diastrophic dysplasia live into adulthood. All will face physical challenges with walking and other movement, and may rely on various mechanical aids for mobility. They usually have normal intelligence and mental function.
People with recessive multiple epiphyseal dysplasia can live normal lifepans and can perform most daily activities, provided these don't stress the joints. Despite joint pain and some bone and joint abnormalities, people with rMED can live normal, healthy lives.