UTP4 and Shwachman-Diamond syndrome: Such threshold variation could be revealed in the setting of haploinsufficiency caused by dominant inheritance of a null allele, such as in Treacher Collins syndrome or Diamond-Blackfan anemia, or with recessive inheritance of partial loss-of-function alleles, such as occurs in Shwachman-Diamond syndrome, and is predicted for NAIC (based on studies with the yeast CIRHIN ortholog Utp4 and the reported lethality of Cirh1a mutant mice) [10,12,29].