Pseudoachondroplasia, which is often called simply PSACH for short, is classified as a rare disorder primarily characterized by short stature. Because it is less rare than many similar diseases, sufficient research has been done to confirm that it is heritable and outline a systematic set of diagnostic criteria.
Definition & Facts
Pseudoachondroplasia has been known since 1959, when Drs. Lamy and Maroteaux first identified it. Today, approximately 1 out of every 30,000 infants may be at risk of developing pseudoachondroplasia. Males and females are affected in equal numbers. While there are a number of disorders that present with symptoms similar to pseudoachondroplasia, this disorder stands on its own and is not connected to any other.
Symptoms & Complaints
While the disorder is heritable and present at birth, it typically does not begin to show itself until the child reaches the age of two or three. This is because developmental delays in stature will not be noticeable before the age of two. At birth, affected infants tend to look totally normal in every way. By age two or three, these and other symptoms may begin to appear:
- Delays in reaching an appropriate developmental height.
- A waddling motion when walking.
- Angular face
- Shorter than typical arms and legs.
- Extensive mobility in joints of the knees, hands, ankles.
- Limited mobility in hips and elbows.
- Hip dysplasia (abnormal hip development).
- Short and stubby fingers and toes.
- Outward (bowed) or inward (knock-kneed) turning legs. (genu varum)
- Abnormalities in the spine and scoliosis (curved spine).
- Joint pain that develops into osteoarthritis.
- Final adult height of less than 4 feet.
Because some symptoms may develop more rapidly than others and the height delay is typically the first and most noticeable symptom, it can take time to determine how severe a case of Pseudoachondroplasia may be.
Pseudoachondroplasia can be either a spontaneous or a heritable disorder. When heritable, it is caused by a mutation in a gene called COMP (cartilage oligomeric matrix protein). This mutation is passed to offspring through an autosomal dominant pattern, which means only one parent must contribute the genetic mutation in order for the offspring to be at risk. Approximately 30 percent of reported cases occur due to the heritable gene mutation.
When spontaneous, the COMP mutation arises on its own without any existing family history of pseudoachondroplasia. Approximately 70 percent of reported cases occur spontaneously. This gene mutation specifically affects height by interfering with the production of cells called chondrocytes, whose job it is to regulate height. The COMP gene is now known to be located within chromosome 19.
In a small number of cases, pseudoachondroplasia can be caused by a condition called germline mosaicism that is present in one or both parents. In this case, only some of the parent's cells bear the COMP mutation while others do not. In families where more than one child develops pseudoachondroplasia, germline mosaicism is always suspected.
Diagnosis & Tests
Diagnosing Pseudoachondroplasia typically cannot happen at birth because the chief symptom, growth delays, has not manifested yet. But as soon as growth delays become apparent, these tests can confirm the cause as pseudoachondroplasia:
- Taking a thorough family history to look for additional cases of pseudoachondroplasia.
- Molecular genetic testing of both parents and the affected individual to look for the COMP gene mutation.
- X-rays to look for growth abnormalities in the skeleton and limb bones.
- Magnetic resonance imaging (MRI) tests to look for skeletal abnormalities.
- Computed tomography (CT) scans to look for skeletal abnormalities.
In cases where there is a family history of pseudoachondroplasia, certain tests can be performed in utero to test for the disorder:
- Chorionic villus sampling. A small tissue sample is taken from the placenta and analyzed.
- Amniocentesis. A small sample of amniotic fluid is taken from the amniotic sac and analyzed.
Treatment & Therapy
Once a diagnosis of pseudoachondroplasia is confirmed, treatment can begin. The treatment plan for each individual can be quite different since the symptoms tend to vary tremendously from case to case.
Typically, a multi-disciplinary treatment team is needed to address different sets of symptoms as they appear. Professionals that are often included on the treatment team can include rheumatologists, orthopedists, neurologists, pediatricians, physical therapists and others as needed.
Some treatments will need to be delayed until later in life, such as hip replacement surgery or knee replacement surgery due to dysplasia and spinal deformities. Often pain medication is given to control joint pain from osteoarthritis. Treatment with braces and/or surgery can be helpful to treat scoliosis and other spinal curvatures. Osteotomy, a surgical procedure that cuts limb bones to support better alignment and growth, can also be helpful.
Prevention & Prophylaxis
In the case of the new class of drugs currently in development, researchers now state that treatment should begin as early as age two for optimal results throughout the individual's lifetime. These drugs show promise in reducing the damage that pseudoachondroplasia can cause to growth plates in the body. In the 30 percent of cases that are linked to a heritable gene mutation, genetic testing can also be seen as a possible effective preventative agent.