Monarch Disease Ontology id MONDO_0014125 (symphalangism, proximal, 1B) is any proximal symphalangism in which the cause of the disease is a mutation in the GDF5 gene. Also known as: GDF5 proximal symphalangism (disease), proximal symphalangism (disease) caused by mutation in GDF5, symphalangism, proximal, type 1B.