A single point mutation within the ED1 gene disrupts correct splicing at two different splice sites and leads to anhidrotic ectodermal dysplasia in cattle

The ectodysplasin I gene (ED1) encodes a signaling molecule of the tumor necrosis factor family that is involved in fetal development of ectodermal appendages. Mutations in the ED1 gene are responsible for X-linked anhidrotic ectodermal dysplasia characterized by impaired development of hair, teeth, and eccrine sweat glands in human, mouse, and cattle. Two isoforms of ectodysplasin 1, termed ED1-A1 and ED1-A2, arise by alternative splicing and bind to different receptors. We identified a novel ED1 splice site mutation in a cattle family with X-linked anhidrotic ectodermal dysplasia. The point mutation is located within a 5' splice site (splice donor) at the beginning of intron 8 that is used exclusively in the alternatively spliced ED1-A1 transcript. Remarkably, cDNA sequencing demonstrated that both physiological transcripts, i.e., the ED1-A1 and the ED1-A2 splice variant, were affected by this point mutation. In an affected animal, the use of cryptic internal splice donor and acceptor sites within exon 8 lead to the production of a single transcript lacking 5 1 or 45 bp with respect to the normal ED1-A1 or ED1-A2 transcripts, respectively. The translated protein of the mutated transcript contained a large deletion in the functionally important C-terminal tumor necrosis factor-like domain thus causing the observed phenotype of anhidrotic ectodermal dysplasia. Our findings suggest the presence of a splice enhancer in the ED1 gene in the region of the mutation.