Only very recently have RNU4ATAC variants been described in foetuses [41]; all four foetuses (two of whom were twins) had severe microcephaly together with some other brain and skeletal abnormalities including corpus callosum agenesis, short limb, brachydactyly and ossification delay, suggestive of a diagnosis of MOPD1. The gene discussed is RNU4ATAC; the disease is microcephaly.