This is because CYP21A2 gene deletions frequently extend into the overlapping TNX gene encoding Tenascin-X, an extracellular matrix protein whose homozygous deficiency causes a severe form of EDS (6) and whose haploinsufficiency causes the mild, “joint hypermobility” form of EDS (7). The gene discussed is TNXB; the disease is Ehlers-Danlos syndrome.