The occurrence of a new mutation affecting cartilage and bone in mice is reported . The gene is lethal, shows autosomal recessive inheritance, and has high penetrance. It is not allelic to shorthead and probably not to phocomelia or achondroplasia . It results in a foreshortened face, cleft palate, defective trachea, and shortened long bones with flared metaphyses . Chondrocytes of epiphyseal cartilage from the mutant are not aligned in columns, and there is a decrease in the usual staining of the cartilage matrix . Electron microscope observations show large, wide collagen fibrils with "native" banding in the matrix of mutant cartilage, which are not present in normal cartilage . Possible explanations for the expression of this genetic disorder of cartilage development are put forward .

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