Aplasia/Hypoplasia of the thumb (HP_0009601) is hypoplastic/small or absent thumb. Also known as: Absent or hypoplastic thumbs, Absent/hypoplastic thumb, Absent/hypoplastic thumbs, Absent/small thumb, Absent/underdeveloped thumb, Aplasia/hypoplasia of thumbs, Aplastic/hypoplastic thumbs, Hypoplastic to aplastic thumbs.