Joint hypermobility and genetic collagen disorders: are they related?
- Hypermobility Clinic, UCL Hospitals, London W1P 9PG, UK
- Professor R Grahame, Department of Rheumatology, Arthur Stanley House, 40–50 Tottenham Street, London W1P 9PG, UK.
Joint hypermobility and genetic collagen disorders: are they related? If this same question had been posed a quarter of a century ago, the answer would have been very different from what is appropriate today. Conventional wisdom1 has always favoured the view that “common” hypermobility merely represents the upper end of a Gaussian distribution of the “normal” joint range of movement. That view is now challenged by the notion that this variety of hypermobility, at least as far as it is seen from the clinic, may represent a departure from “normality”. The inference is that it is a forme fruste of a genetic connective tissue disease (or heritable disorder of connective tissue (HDCT)). This does not, of course, exclude the possibility that “common” hypermobility, such as is seen in musicians and dancers, may be non-pathogenic polymorphisms, as a result of minor variations in extracellular matrix genes such as collagens, elastin, fibrillins, etc. Other variations might be in different, more interactive regions of the protein and are then pathological.
Joint hypermobility
A hypermobile joint is one whose range of movement exceeds the norm for that individual, taking into consideration age, sex, and ethnic background. The maximal range of movement that a joint is capable of is determined by the tightness or otherwise of the restraining ligaments. Thus, the primary cause of hypermobility is ligamentous laxity. This is inherent in a person’s make up and is determined by their fibrous protein genes. Of particular importance in this respect are the genes that encode collagen, elastin, and fibrillin.
In general, joint laxity is maximal at birth, declining rapidly during childhood, less rapidly during the teens, and more slowly during adult life.2 Women are generally more lax jointed than men at all ages and there is wide ethnic variation. Epidemiological studies have shown that hypermobility …
