Just read this article posted on the IV IONS Board by "arthurs1".
It is worth reading in its entirety in my opinion.
Just a snippet from article
"Testing requirements for ultra-rare disease therapies like the ASOs pursued by n-Lorem will have implications beyond just a handful of patients. In an editorial accompanying Yu’s paper, Janet Woodcock, and Peter Marks from the FDA’s Center for Drug Evaluation and Research, wrote that “programs for a single patient are likely to set the floor for the minimum preclinical evaluation.” They added that although in the near term ultra-rare therapies could exist as investigational drugs only, regulatory approval would become more pertinent if similar interventions begin to proliferate.