Cyt c deficiency in mice causes embryonic lethality and attenuates stress-induced apoptosis [55]. Mice expressing mutant cyt c (KA allele) that retains the electron transfer function, but is incapable of Apaf-1 activation [56]: • exencephaly and hydrocephalus, • cachexia, • lymphopenia. This evidence concerns the gene APAF1 and lymphopenia.