A previous detailed study indicated that the carboxyl-terminus of MeCP2 is required for the interaction with FBP11, the protein product of PRPF40A (Pre-mRNA Processing Factor 40 Homolog A) and HYPC, the protein product of PRPF40B (Pre-mRNA Processing Factor 40 Homolog B)56; as the truncation of the carboxyl-terminal 86 amino acids containing the WW protein interaction domain of MeCP2, which also results from a frameshift mutation present in a group of Rett syndrome patients, abrogates interactions with FBP11 and HYPC. The gene discussed is PRPF40B; the disease is atypical Rett syndrome.