Why is it that often times kids with juvenile arthritis also have hypermobility?

Possible genetic: There appears to be an inherited pattern for the inflammatory arthritis syndromes, including JA, and hypermotile joints also tend to run in families. Although many people with Hypermotility often have many musculoskeletal pains that are not JA, a recent study did find an increase incidence of JA and HS: https://www.ncbi.nlm.nih.gov/pubmed/28052441