The surprising dichotomous discovery of increased neurite outgrowth, a specific gain-of-toxic-function associated with the p.Pro403* mutation in ADNP, contrasting the cell survival deleterious effect of the p.Tyr718* mutation, may be related to the two distinct and partially opposing genomic DNA methylation epi-signatures in ADNP syndrome blood. This evidence concerns the gene ADNP and ADNP-related multiple congenital anomalies - intellectual disability - autism spectrum disorder.