Hello: Read what he quoted in Anaf 8 from the Beis Yehudah and what he says about Al Y’dei Sam. He gives the situations in which he is Mattir even without Sakanah.
Tomche and Chacham: The Tzitz Eliezer first gave his P’sak that it was okay for Tay-Sachs and I believed published it. In the Igros (Choshen Mishpat 2:69 if I recall correctly) R’ Moshe writes a lengthy Tshuvah about it and ends by saying he went to these lengths because he heard that a Rabbi in Sha’arei Tzedek hospital was Mattir. The Tzitz Eliezer responds and explains using some very strong Leshonos why, in his opinion, Rav Moshe’s argument wasn’t really an argument. There was no further discussion as their wasn’t really a need for it. Both had made their cases quite clear. Because of the nature of this argument, any further response by R’ Moshe would not have added anything to the issue.