Pseudoachondroplasia is characterized by severe growth deficiency and deformations such as bow legs and hyperlordosis.
Prevalence is estimated at around 1/60,000.
The disorder is usually discovered during the second year of life with the onset of slow growth and walking difficulties. The short stature becomes more prominent with age and the hands and feet appear short and wide. Joint laxity is a general feature, but predominantly affects the hands. Defective epiphyseal growth causes early arthrosis. The limb deformation is caused by metaphyseal lesions.
The disorder is caused by small mutations or deletions in the COMP gene (19p13.1) coding for the cartilage oligomeric matrix protein.
Diagnosis is made on the basis of epiphyseal and metaphyseal anomalies detected on radiographs during the second year of life.
The principle differential diagnosis is achondroplasia (see this term), but the craniofacial anomalies present in this disorder are absent in patients with pseudoachondroplasia and radiographic findings differ significantly. Forms of multiple epiphyseal dysplasia (see these terms) may also be included in the differential diagnosis.
Prenatal diagnosis is feasible if the mutation has been detected in an affected parent.
Transmission is autosomal dominant, but most isolated cases are due to de novo mutations. Genetic counseling may be proposed and the recurrence risk is 50%.
Treatment is based on physiotherapy, management of the spinal deformation and corrective orthopedic surgery. Intensive physical activity should be avoided. The limb deformation should be corrected surgically at the end of the growth period.
The final height prognosis is variable but the short stature may be moderately severe.
Last update: November 2008