Type I, or Gravis variety, is the classic, severe disorder characterized by marked skin hyperextensibility and joint hypermobility. The skin is typically soft and velvety in texture with increased compliance. Easy bruisability is common and trauma results in gaping, fish-mouth type wounds which bleed less than expected. Prematurity is common, presumably because of fragility of the fetal membranes. Type I is inherited in an autosomal dominant manner with complete penetrance.
New mutations are common.
No distinctive biochemical tests are available, but the diagnosis generally is not ambiguous. The clinical features of type II, the Mitis form, are similar to those of EDS Type I, but milder. It, too, is inherited in an autosomal dominant fashion. The ultrastructural features are similar to type I, and the biochemical etiology remains unknown. Type III EDS, benign familial hypermobility, is an autosomal dominant disorder in which the major clinical features are large and small joint hypermobility.