Does the Federal Death Penalty Act prohibit the execution of a federal prisoner who is intellectually disabled?

QUESTIONS PRESENTED Does the Federal Death Penalty Act, which provides that a “sentence of death shall not be carried out upon a person who is mentally retarded,” prohibit the government from executing a federal prisoner who is intellectually disabled under current legal and diagnostic standards? If so, does 28 U.S.C. § 2241 provide a remedy for such a prisoner when a court had previously denied his claim using now-rejected judge-made criteria instead of clinically accepted diagnostic standards? i