from Wikipedia:
Ectodermal dysplasia is not a single disorder, but a group of syndromes all deriving from abnormalities of the ectodermal structures.[1]:570 More than 150 different syndromes have been identified.[2]
Despite some of the syndromes having different genetic causes the symptoms are sometimes very similar. Diagnosis is usually by clinical observation often with the assistance of family medical histories so that it can be determined whether transmission is autosomal dominant or recessive.
One of the problem seems to be that there are different causes so you'd have to make an individualized therapy... $$$
crispr - there was some talk about it here. Introducing a foreign protein into an adult animal probably is not a good idea - immune reaction that could lead to necrosis or even cytokine storm - probably much worse than ED...
There once was a paper about distributing correcting mRNAs over the blood stream... I don't remember how it was called and how effective it was. But the theory is, you transform e.g. only the liver with the correct mRNA, it is distributed by the blood to the skin.