Microcephaly-brain defect-spasticity-hypernatremia syndrome is a rare congenital genetic syndrome with a central nervous system malformation as a major feature characterized by microcephaly, hypertonia, developmental delay and cognitive impairment, swallowing difficulty, hypernatremia, and hypoplasia of the frontal parts and fusion of the lateral ventricles on brain MRI. Only one familial case with three affected siblings reported and there have been no further descriptions in the literature since 1986. The disease is microcephaly-brain defect-spasticity-hypernatremia syndrome (MONDO_0016758, a Monarch Disease Ontology id). Also known as: Franek-Bocker-Kahlen syndrome.