Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by homozygous or compound heterozygous mutations in one of three genes: PHGDH, PSAT1 and PSPH[4][5] These genes are involved in the serine biosynthesis pathway and are essential for cell proliferation. Mutations in all three genes had been previously identified as the cause of serine-deficiency syndromes. Although there is some clinical overlap between NLS and these neurometabolic disorders, the phenotype in other serine-deficiency disorders is milder.