Rhizomelic chondrodysplasia punctata

Rhizomial chondrodysplasia is a form of chondrodysplasia punctata, a group of congenital diseases that lead to punctiform calcifications of cartilage tissue in the joints, larynx and trachea.

The disease is characterized by rhizomelic dwarfism (shortened humeri and femura), vertebral lesions, bilateral symmetric cataracts, ichthyosiform lesions, severe mental retardation, and lack of psychomotor development. The rhizomelic type of chondrodysplasia punctata is due to an autosomal recessive inherited disordered peroxisomal transformation.

After the localization of the triggering mutation, a subdivision into 3 types occurs:

Type I is the most common form and has mutations in the PEX7 gene (Peroxisomal biogenesis factor-7), which affects the PTS2 receptor. This plays an important role in the protein import of peroxisomes.

Type II is based on mutations in the GNPAT gene (glycerone phosphates O-acyltransferase gene), which encodes the dihydroxyacetone phosphate acyltransferase.

Type III has mutations in the AGPS gene which alters the peroxisomal alkyl dihydroxyacetone phosphate synthase. Biochemically, there is an increase in phytanic acid in the plasma, a reduced synthesis of plasmalogen and defective oxidation of phytanic acid in fibroblasts.