Summary
Cartilage-hair hypoplasia is a disease affecting the bone metaphyses causing small stature from birth. Prevalence is unknown. The disease is associated with fine, slow growing hair, and sometimes with immune deficiencies. Other symptoms include short hands and possibly short, deformed limbs (varus). X-ray reveals metaphyseal lesions, especially in the knees, and large, round epiphyses during childhood. Short stature is common and has very early onset but immune deficiency is not always present. The disease course is variable. Cartilage-hair hypoplasia is inherited in an autosomal recessive manner. Mutations in the RMRP (RNA component of mitochondrial RNA-processing endoribonuclease) gene, which maps to the 9p21-p12 locus, are responsible for the disease. The diagnosis is confirmed by direct sequencing of the RMRP gene. The differential diagnosis should include other forms of short-limb dwarfism. A recurrence risk of 25% justifies prenatal diagnosis, which is possible through molecular analysis if the causative mutation has already been identified in a proband. Micromelia may be detected early in pregnancy during ultrasound follow up, but is not specific. Immunodeficiency, when severe, may require bone marrow transplantation but this does not have any effect on the growth deficiency. The prognosis depends on the presence and severity of the immune deficiency and the possible association with Hirschsprung disease (see this term). *Author: Prof. M. Le Merrer (November 2008)*.
