TNNI2 and Sheldon-hall syndrome: Approximately 20% of familial incidences of DA2B can be explained by mutations in TNNI2 that encodes a subunit of the troponin complex consisting of troponin C, troponin I and troponin T. Troponin complex is set of muscle proteins that are part of the contractile apparatuses for contraction of fast skeletal muscle.