Dyssegmental dysplasia, Silverman-Handmaker type (DDSH), is a lethal autosomal recessive form of dwarfism with characteristic anisospondylic micromelia. The remarkable similarities in the radiographic, clinical, and chondroosseous morphology of DDSH patients to those of perlecan-null mice led to the identification of mutations in the perlecan gene (HSPG2) of DDSH. Perlecan, a large heparan sulfate proteoglycan, is expressed in various tissues and is a component of all basement membrane extracellular matrices. A chondrodysplasia phenotype caused by the loss of perlecan was unexpected, because cartilage does not have basement membranes. Insertion and splicing mutations in HSPG2 of DDSH were found that were predicted to create a premature termination codon. Immunostaining and biochemical analysis revealed that the mutant perlecan molecules were unstable and not secreted into the extracellular matrix. These results indicate that DDSH is caused by functional null mutations of HSPG2 and that perlecan is essential for cartilage development. Published 2002 Wiley-Liss, Inc.