Orphanet_79507 (Hypotonia - failure to thrive - microcephaly) can be described as follows. Leukotriene C4 synthase deficiency is an extremely rare fatal neurometabolic developmental disorder characterized clinically by muscular hypotonia, psychomotor retardation, failure to thrive, and microcephaly. Also known as: LTC4 synthase deficiency, Leukotriene C4 synthase deficiency.