Polyarticular osteoarthritis--two major phenotypes hypothesized.

Osteoarthritis is the commonest form of arthritis, at least amongst Caucasians and is frequently polyarticular. Genetic factors are now considered pivotal in the aetiopathogenesis of polyarticular osteoarthritis (POA). This document proposes a nexus between the gene most commonly mutated amongst Caucasian peoples, notably the HFE gene and an appreciable subset of POA patients who have a clinically recognisable OA phenotype. It is hypothesised that there are at least 2 major POA phenotypes each of which is associated with discrete genotypes. Type 1 POA characterized by Heberden's or Bouchard's nodes with prominent DIP, PIP, knee joint (medial compartment) and Great toe MTP joint involvement corresponds to the putative nodal generalized form of OA or NGOA (proposed Type 1 POA phenotype). As yet no genetic marker has been defined for this POA subset. The second is a hitherto less well recognized phenotype characterized by involvement of the index and/or middle finger metacarpophalangeal (MCP2,3) joints and the elbows, ankles and possibly the intertarsal and tarsometatarsal joints. The hip and knee joints may sometimes also be involved. This different joint distribution corresponds closely to the pattern observed in the arthropathy that often accompanies hereditary haemochromatosis. It is predicted that mutations in the HFE gene will associate strongly with the proposed Type 2 POA phenotype and serve as a genetic marker for this clinically recognisable subset.