Serine-deficiency syndrome is a very rare infantile-onset potentially treatable neurometabolic disorder characterized clinically by microcephaly, neurodevelopmental disorders and seizures. Three serine-deficiency syndromes have been described: 3-phosphoglycerate dehydrogenase (3-PGDH) deficiency, 3-phosphoserine phosphatase (3-PSP) deficiency, and phosphoserine aminotransferase deficiency (see these terms).