RMRP related disorders - The RMRP gene encodes an RNA component of an enzyme involved in the processing of mitochondrial RNA. Mutations in RMRP have been identified in three different disorders: Cartilage-hair hypoplasia or metaphyseal chondrodysplasia, McKusick type (CHH; MIM 250250), metaphyseal dysplasia without hypotrichosis (CHHV; MIM 250460) and anauxetic dysplasia (MIM 607095). All are autosomal recessive disorders.

Cartilage-hair hypoplasia (CHH) has a variable presentation. It is a skeletal dysplasia characterized by short extremities, bowed legs, short and broad hands and feet, extreme ligamentous laxity and hypoplastic hair. Additional findings may include Hirschsprung disease, hypopigmented skin, various defects of cellular immunity and anemia. Metaphyseal dysplasia without hypotrichosis (CHHV) is an autosomal recessive disorder recognized as a variant of CHH. The phenotype of CHHV also overlaps with that of metaphyseal chondrodysplasia, Schmid type (MCDS; MIM 156500). Anauxetic dysplasia is characterized by prenatal onset of severe disproportionate short stature with an adult height of <85 cm, hypodontia and mild mental retardation. Other findings include platyspondyly, cervical dislocations, hypoplastic ilia, small epiphyses, metaphyseal flaring and brachydactyly.