(A) Mutation analysis in the Fas gene. Sequence analysis performed with the Automated Laser Fluorescent A.L.F. DNA Sequencer on amplified genomic fragments encompassing nt 543-569 and nt 876-902 of the Fas cDNA is shown. (B) Sequence of human and murine Fas cDNA at the N-terminus of the death domain. The conserved amino acids are boxed. The arrow indicates the tyrosine that is mutated to cysteine in the three affected siblings and in their father.