While deletion of Gldc has been previously shown to cause neural tube defect that may be rescued by formate treatment of dams[25,28], we provide the first evidence that severe mutation-induced neurological disease in NKH is principally due to prenatal defects (milder forms of which could induce post-natal hydrocephalus) and that the WMMS in the C57BL/6 strain provides a predictor of fatal, prenatal defect/disease. The gene discussed is GLDC; the disease is Hydrocephalus.