Heritable osteoarthritis. Diagnosis and possible modes of cell and gene therapy

Abstract

Our goals for osteoarthritis (OH) are straightforward: we need to define the causes of the disease and/or ‘the cascade of events’ that produce the degeneration of joint cartilage. From there we need to move on to methods of preventing or curing the disease. As is well recognized, there are multiple causes for the degeneration of joint cartilage seen in OA. One of the hypotheses that we have pursued is that genetic mutations produce OA in a subset of patients with early onset forms of the disease. Another hypothesis we have pursued is that genetically caused OA may be the easiest target for both diagnosis and therapies for the disease. Accordingly, we began several years ago to use the candidate gene strategy to search for mutations in the gene for type II procollagen (COL2A1) in patients with early onset OA. In a proband referred to us by Dr Roland Moskowitz and his colleagues at Case Western Reserve, we located a single-base substitution that converted a codon for arginine to a codon for cysteine at the α1-519 position in the triple helix of the protein. The detection of the cysteine substitution suggested that the mutation was a disease-causing change because cysteine is not found in the interior of the triple helix of any fibrillar collagen. However, in common diseases such as OA it is frequently very difficult to be certain that a change seen in a gene does in fact cause the disease. Fortunately, Dr Moskowitz and his colleagues were able to provide us with data on the patient’s family, and it was possible to show that the mutation was co-inherited with the disease in a statistically convincing manner (lod score of greater than 3.0). Eyre et al. demonstrated that type II collagen extracted from the patient’s cartilage formed abnormal disulfide bonds. Subsequently, we were able to demonstrate that the mutation generates abnormal fibrils in a purified system for assembly of type II collagen fibrils. Examination of the fibrils by atomic force microscopy demonstrated that the mutated protein has the unusual effect of increasing the depth of the gap region in collagen fibrils (E. Adachi, O. Katsuma, S. Yamashina, D. J. Prockop, and A. Fertala, submitted for publication). More recently, we developed a line of transgenic mice expressing the mutated gene. Our preliminary observations on the transgenic mice suggest that they develop cartilage changes that resemble OA (S.-W. Li, M. Arita, L. Ala-Kokko, D. J. Prockop, in preparation). Therefore, we now have thoroughly convincing data that the mutation in this family caused the clinical syndrome of early onset OA associated with evidence of a