While Mbnl1/Mbnl2 double knockout (DKO) mice were embryonic lethal, the inactivation of one Mbnl2 copy in a Mbnl1 KO background was sufficient to exacerbate myotonia and trigger muscle weakness, loss of mature neuromuscular junctions and cardiac conduction defects, which were absent in single Mbnl1 KO mice (21, 57). The gene discussed is MBNL2; the disease is Myotonia.