Hypermobile Ehler-Danos Syndrome and Hypermobility Spectrum Disorder

Practice and progress in rheumatology

The relationship between hypermobile Ehler’s-Danlos Syndrome (hEDS) and Hypermobility Spectrum Disorder (HSD) has been hotly debated in recent years, with research being published on a near-constant basis attempting to establish a valid symptomatological or causalogical  difference between the two disorders. Now, a paper by Ritelli et al. (2022) threatens to end the savage cycle for all. Using RNA sequencing techniques and immunofluorescence, Ritelli et al. found identical gene expression and cellular characteristics in dermal biopsies from those with both conditions. Through immunofluorescence of biopsies from 20 women with hEDS, 16 women and 4 men with HSD and 40 controls, it was found that the shape and components of the extracellular matrix were greatly different in those with HSD/hEDS in comparison to those in the healthy control group. 

Abnormalities were discovered in the expression of cadherin-11, snail1, and αvβ3, α5β1 and α2β1 integrins. Integrins mediate the connections between the cell cytoskeleton and extracellular matrix to ensure they stay together, cell-to-cell adhesion is initiated by cadherin-11, and snail1 is localised close to the cyclin-dependent kinase inhibitor 2B (CDKN2B) gene. Snail1 can activate CDKN2B gene products when Snail1 is overexpressed to the point of reaching the general localisation of the CDKN2B domain. This demonstrates that there may be a similar causative link between the widespread inflammation and chronic pain in HSD/hEDS and rheumatoid arthritis. Li et al. (2021) proved that the polarisation of macrophages (white blood cells which destroy foreign products) was carefully controlled by the CDKN2B-AS1/ MIR497/TXNIP axis- the increased activation of which in rheumatoid arthritis catalyses the excessive polarisation of macrophages, which causes the macrophages to attack healthy cells.

In rat studies published by Tan et al. (2022), it was found that rats with diabetes and induced sepsis experienced greater intestinal injury that control rats without any medical pathology who experienced induced sepsis. This was demonstrated to be due to interruptions in the miR-3061/Snail1 communication pathway. 

Research on this phenomenon in humans may elucidate the relevance of snail1 overproduction in hEDS/HSD sufferers to their complex gastrointestinal symptoms. If this pathway works similarly in human models of sepsis or localised GI infection, it may intimate that snail1 overproduction is responsible for the hyperpolarisation of macrophages in response to foreign product detection, which may cause immunological damage in the intestines. However, the relevance of this study to hEDS/HSD should be considered questionable until further human research into this avenue has been completed.

The result of this research is that academia can potentially derive a genetic cause of the complex phenotypes demonstrated by sufferers of hEDS/HSD. This can be achieved by visualising the human genome, and testing genes like those above, or those implicated in modulating the activity of the genes above. Once garnered, this genetic evidence will elucidate whether or not hEDS and HSD are one disorder, or both variants of the same disorder with differing genetic causes. This, in turn, could lead to the development of medications or treatments based on genetic phenotype. 

Written by Aimee Wilson