SON and multiple congenital anomalies/dysmorphic syndrome-intellectual disability: The mutations found to be associated with ZTTK syndrome are mostly frameshift mutations and nonsense substitutions generating a premature termination codon [1–6], and transcripts of the mutant gene seem to be degraded due to nonsense-mediated mRNA decay (NMD) [1]; this has made ZTTK syndrome to be regarded as an entity caused by SON haploinsufficiency.