NTDs and hydrocephalus have both been associated with GCS mutation in humans,7, 11, 13 and we previously reported the corresponding presence of cranial NTDs and enlarged cerebral ventricles in Gldc mutant mice.14 However, the stage at which hydrocephalus develops in the mouse model had not been established, and this was complicated by the partial penetrance of this defect, which means that affected embryos could not be reliably identified soon after onset. The gene discussed is GLDC; the disease is Hydrocephalus.