Disclosed are methods and compositions for early diagnosis, monitoring and treatment of cartilage degenerative conditions, including forms of arthritis. In particular, the invention relates to a protein, termed "adlican," that is differentially transcribed and expressed in human subjects suffering from arthritis, such as osteoarthritis (OA) and rheumatoid arthritis (RA) compared with non-arthritis sufferers, antibodies which recognize this protein, and methods for diagnosing arthritis.