Diastrophic dysplasia: evidence against a defect of type II collagen

A description of an abnormal segment-long-spacing crystallite (SLS) pattern has been reported for type II collagen from patients with diastrophic dysplasia (Stanescu et al., 1982 a), a disorder that is characterized by large collagen fibrils in the cartilage matrix. The abnormal SLS consisted of an altered electron density between bands 42 and 45, which was interpreted as an abnormality in the type II collagen molecule. It was suggested that the type II collagen is abnormal in diastrophic dysplasia. We have examined SLS of type II collagen from two patients with diastrophic dysplasia and found the SLS patterns to be identical with that of control type II SLS in almost all micrographs. In a few micrographs of diastrophic SLS, crystallites exhibiting the pattern reported by Stanescu et al. were seen. However, the abnormally patterned crystallites always consisted of dimers that were overlapped at the COOH ends in such a way that an electron dense band of one crystallite was positioned between bands 42 and 45 of the second crystallite, apparently creating the abnormal pattern. The abnormal SLS pattern seen in these cases of diastrophic dysplasia appears to be the result of overlapping crystallites and may not be the result of an intrinsic abnormality of type II collagen. We have constructed histograms of the collagen fibril diameters in diastrophic cartilage. While they are larger than normal collagen fibrils, this by itself does not indicate an abnormality of type II collagen. We have shown that large fibrils such as these can be obtained from normal type II collagen when the structure of the cartilage is disrupted by extraction with guanidine.(ABSTRACT TRUNCATED AT 250 WORDS)