Craniosynostosis is a primary abnormality of skull growth involving premature fusion of the cranial sutures such that the growth velocity of the skull often cannot match that of the developing brain. This produces skull deformity and, in some cases, raises intracranial pressure, which must be treated promptly to avoid permanent neurodevelopmental disability (summary by Fitzpatrick, 2013). Craniosynostosis-6 is a bicoronal form associated with bony defects in the sagittal, metopic, or lambdoid sutures (Twigg et al., 2015). For a discussion of genetic heterogeneity of craniosynostosis, see CRS1 (123100). Structural brain anomalies with impaired intellectual development and craniosynostosis (BAIDCS; 618736) is an allelic disorder.