TTN and skeletal muscle disorder: Other skeletal myopathies caused by missense mutations in titin include tibial muscular dystrophy due to heterozygous mutations in the C-terminus3 and limb-girdle muscular dystrophy type 2J arising from recessive mutations at the same locus.4 Cardiac complications in these phenotypes have not been reported previously.1,3, –, 5 Conversely, heterozygous truncating TTN mutations are a recognized cause of dilated6 and restrictive7 cardiomyopathies without apparent skeletal muscle involvement.