Mutations leading to X-linked hypohidrotic ectodermal dysplasia affect three major functional domains in the tumor necrosis factor family member ectodysplasin-A

Mutations in the epithelial morphogen ectodysplasin-A (EDA), a member of th e tumor necrosis factor (TNF) family, are responsible for the human disorde r X-linked hypohidrotic ectodermal dysplasia (XLHED) characterized by impai red development of hair, eccrine sweat glands, and teeth. EDA-A1 and EDA-A2 are two splice variants of EDA, which bind distinct EDA-A1 and X-linked ED A-A2 receptors. We identified a series of novel EDA mutations in families w ith XLHED, allowing the identification of the following three functionally important regions in EDA: a C-terminal TNF homology domain, a collagen doma in, and a furin protease recognition sequence. Mutations in the TNF homolog y domain impair binding of both splice variants to their receptors, Mutatio ns in the collagen domain can inhibit multimerization of the TNF homology r egion, whereas those in the consensus furin recognition sequence prevent pr oteolytic cleavage of EDA. Finally, a mutation affecting an intron splice d onor site is predicted to eliminate specifically the EDA-A1 but not the EDA -A2 splice variant. Thus a proteolytically processed, oligomeric form of ED A-A1 is required in vivo for proper morphogenesis.