Monarch Disease Ontology identifier MONDO_0017498 (congenital absence of both forearm and hand, unilateral) is a rare developmental defect during embryogenesis characterized by a unilateral, transverse absence of the radius and ulna (of varying terminal lengths), as well as all the elements composing the hand. Left or right side may be involved. Also known as: radio-ulnar terminal transverse meromelia, unilateral.