Neu-Laxova syndrome (NLS) is an autosomal recessive disorder characterized by severe congenital malformations leading to prenatal or early postnatal lethality. Main findings include intrauterine growth retardation, microcephaly, ichthyosis, flexion deformities, edema of the hands and feet, and abnormal facial features including abnormal or absent eyelids, flat or abnormal nose, and a round gaping mouth. NLS1 (MIM 256520) and NLS2 (MIM 616038) are caused by mutations in the PHGDH and PSAT1 genes.  They code for D-3-phosphoglycerate dehydrogenase and phosphoserine aminotransferase enzymes, respectively. These enzymes are involved in L-serine biosynthesis. Phosphoglycerate dehydrogenase deficiency (PHGDHD; MIM 601815) and phosphoserine aminotransferase deficiency (PSATD; MIM 610992) are autosomal recessive disorders allelic to more severe disorders, NLS1 and NLS2. PHGDHD and PSATD are characterized by congenital microcephaly, hypertonia, psychomotor retardation and seizures.