Cartilage-Hair Hypoplasia Syndrome
|Disease group||Ectodermal Dysplasia|
|DISEASE NAME||CARTILAGE-HAIR HYPOPLASIA|
|Synonymous||Metaphyseal Chondrodysplasia, McKusick Type|
|Gene (s)||RMRP (157660)|
Cartilage-hair hypoplasia (CHH) is a rare autosomal recessive ectodermal dysplasia disorder. Also known as metaphyseal chondrodysplasia, CHH was first identified in 1965 by McKusick et al. presents with short-limbed dwarfism, sparse hypochromic hair and T and/or B-cell immunodeficiency. Mutations in the gene for RMRP (RNase RMP) have been identified as the molecular basis for this inherited disorder.
Children born with CHH may be subject to opportunistic infections due to immunodeficiency with a reportedincreased susceptibility to varicella-zoster infection. Several reports of increased susceptibility to malignancies suchas leukaemia and non-Hodgkin's lymphoma have also been documented. Gastrointestinal defects can occur and mayinclude Hirschprung's disease and malabsorption. Varying degrees of anaemia and/or neutropenia may present in childhood which requires careful inpatient management.
In 2001, Ridanpaa et al. reported mutations in the RMRP gene on locus 9p21-p12 as the molecular basis of CHH. RMRP is a ribonucleoprotein required for cell growth and, in 2005, Thiel et al. showed that different RMRP gene mutations led to decreased cell growth by impairing ribosomal assembly and by altering cyclin-dependent cell-cycle regulation.
Diagnosis is usually made at birth, though the clinical features of short-limbed dwarfism may also be detected in utero. Skeletal radiology is the most useful diagnostic tool and shows shortened long tubular bones, a curved femur with rounded distal epiphyses, anterior angulation of the sternum and short ribs. Flaring of the ribs at the costochondral junction is also characteristic. Sequencing of genomic DNA for RMRP mutation analysis will help confirm the diagnosis and will aid in genetic counseling.
The mainstay of treatment is the careful monitoring and treatment of opportunistic infection (especially varicella Zoster) and malignancy. Patients should be monitored for lymphopaenia, neutropaenia and anemia - all of which may occur early in infancy.