TGIF1 and holoprosencephaly: These data suggest that TGIF alterations explain only a very small proportion of HPE cases, and TGIF involvement in HPE can be discussed since only 10% of patients carrying a 18p deletion (including the TGIF gene) present HPE [61,62] and mouse models with disrupted entire Tgif do not present an HPE phenotype [63].