Abnormal electrophoretic mobility of the proa1(V) or proa2(V) chains of collagen type V has been detected in several but not all families with the Classical Type. Because a highly sensitive screening method has not yet been developed, the absence of detected abnormalities by biochemical or molecular analysis does not rule out a defect in collagen type V. In informative families genetic linkage studies can be used for prenatal and postnatal diagnosis. Mutation analysis in individuals is being performed on a research basis. Locus heterogeneity has been documented (Steinmann et al., 1993). Genetic linkage to intragenic markers of the COL5A1 or COL5A2 genes has been excluded in some families. Abnormalities in the collagen fibril structure can be found in many families by electron microscopy; a "cauliflower" deformity of collagen fibrils, is characteristic but not specific.