Dermatosparaxis is a heritable disorder of the connective tissue observed in the calf and is related to the presence in the dermis of a form of procollagen, rather than collagen, forming the fibrous support of the skin. This alteration results from the lack of activity of procollagen peptidase, an enzyme required for the final processing of procollagen in collagen. Skin in dermatosparaxis displays abnormal mechanical properties. Procollagen forms poorly structured fibers loosely packed in sheets and dispersed within an excess of glycosaminoglycans. This disturbed architectural organization is responsible for the hyperextensibility and poor elasticity of the dermatosparactic dermis. Skin fragility is related to the impaired mechanical properties of the procollagen polymers. Rupture occurs in the mid-dermis in a location where the connective tissue is devoid of adnexae and elastic fibers.