Deconstructing and reconstructing joint hypermobility on an evo-devo perspective.

Abstract

Joint hypermobility is a common characteristic in humans. Its non-casual association with various musculoskeletal complaints is known and currently defined as the spectrum . It includes hypermobile Ehlers-Danlos syndrome (hEDS) and hypermobility spectrum disorders (HSD). hEDS is recognized by a set of descriptive criteria, while HSD is the background diagnosis for individuals not fulfilling these criteria. Little is known about the etiopathogenesis of the spectrum . It may be intended as a complex trait according to the integration model. Particularly, the spectrum is common in the general population, affects morphology, presents extreme clinical variability, and is characterized by marked sex bias without a clear Mendelian or hormonal explanation. Joint hypermobility and the other hEDS systemic criteria are intended as qualitative derivatives of continuous traits of normal morphological variability. The need for a minimum set of criteria for hEDS diagnosis implies a tendency to co-vary these underlying continuous traits. In evolutionary biology, such a covariation (i.e. integration) is driven by multiple forces, including genetic, developmental, functional and environmental/acquired interactors. The etiopathogenesis of the spectrum may be resolved by a deeper understanding of phenotypic variability, which, superimposes with normal morphological variability.