TNXB and connective tissue disorder: TNXB mutations affecting both alleles cause a severe autosomal recessive form of Ehlers–Danlos syndrome (EDS), a connective tissue disorder characterized by hypermobile joints and tissue fragility [7] and a subset of those with the hypermobility type have been found to have TNXB haploinsufficiency with reduced serum levels of TNX [8].