P5CS deficiency (MONDO_0100126) is an inborn error of proline/orinthine metabolism that covers a wide spectrum of phenotypes and is caused by pathogenic variants in the aldehyde dehydrogenase 18 family member A1 (ALDH18A1) gene. These variants lead to a variety of neurocutaneous and motor syndromes characterized by cutis laxa, connective tissue weakness, facial dysmorphism, growth restriction, developmental delay, cataracts, hypotonia, hypertonia, and amyotrophy. Also known as: delta1-pyrroline-5-carboxylate synthetase deficiency.