Maternal phenylketonuria is a group of congenital malformations that occur in children of mothers with untreated hyperphenylalaninemia or phenylketonuria (an autosomal recessively inherited disorder of phenylalanine metabolism caused by the mutation in the phenylalanine hydroxylase (PAH) gene) [15,16,17]. The gene discussed is PAH; the disease is Hyperphenylalaninemia.