Cartilage-hair hypoplasia
Overview
Cartilage Hair Hypoplasia is a rare syndrome affecting the immune system and causing skeletal dysplasia. It is also known as Metaphyseal Chondrodysplasia-McKusick Type . CHH is a recessive gene which means that both parents would have to be carriers of the gene.
Causes
Cartilage-hair hypoplasia is an autosomal recessive inherited disorder. In 2001, Ridanpaa et al identified mutations in the RNA component of the gene for RNase MRP on chromosome band 9p13 as the genetic defect in Finnish patients with cartilage-hair hypoplasia.4 RNase MRP has 2 functions, cleavage of RNA in mitochondrial DNA synthesis and nucleolar cleaving of pre-rRNA.
Prognosis
Adult height ranges between 111 and 151 cm in males and between 104 and 137 cm in females. No more than 20% of CHH patients exhibit recurrent and severe infections. These patients show evidence of immune deficiency in vivo and in vitro.
Treatment
- Disproportionate short stature: Treatment with growth hormone is likely not beneficial in children with CHH. Surgical bone lengthening is occasionally considered. - Orthopedic problems: The lumbar lordosis and ligamentous laxity can cause joint pains of the lower spine, the knees and ankles. - Immunodeficiency: The cellular immunity may be defective whereas the humoral immunity is usually intact. However, there are a few cases that have combined immune deficiency. - Vaccination: immunization with live vaccines is contraindicated in patients with impaired cellular immunity. - Anemia: Patients with severe anemia (5% of CHH patients) require repeated transfusions. A few cases might need lifelong transfusions and/or bone marrow transplantation. - Gastrointestinal dysfunction: This can present with signs of malabsorption, diarrhea, celiac disease, and failure to thrive. This requires symptomatic treatment. It also may present as Hirschsprung?s disease that can be surgically corrected. - Malignancies: Patients should be monit