We sought to determine whether sequence variations in cartilage collagen genes are associated with primary, early-onset osteoarthritis (OA).
The cartilage collagen genes, COL2A1, COL9A1, COL9A2, COL9A3, COL11A1 and COL11A2, were screened for sequence variations in 72 Finnish probands and one US family with primary early-onset hip and/or knee OA. In addition, allelic association studies were performed using six to 12 common polymorphisms from each gene by genotyping 72 OA patients and 103 controls.
Altogether 239 sequence variations were found, of which 16 were not present in the controls. Seven of the unique variations, four in COL11A1, two in COL11A2 and one in COL2A1, were studied further, because they resulted in the substitution of conserved amino acids or were predicted to affect mRNA splicing. Co-segregation of a sequence variation and the phenotype was found in all four families available for study. Association analysis failed to identify any common predisposing alleles.
Early-onset OA demonstrates locus and allelic heterogeneity since the identified variations were in three different collagen genes and each of the six probands had a different mutation. It is also possible that some OA cases represent the mild end of the chondrodysplasia phenotypic spectrum. The major susceptibility alleles in this form of OA, however, remain to be identified.