TNNI3 and cardiac arrhythmia: Larger CTG expansions are associated with shorter life expectancy in DM1,[50] and those with the severe, congenital onset form are much more likely to die from respiratory complications than cardiac arrhythmia, cardiomyopathy or sudden unexplained death.[51] The absence of high cTnI levels in those with very large repeat expansions therefore may simply reflect a lower burden of progressive cardiac disease due to reduced long-term survival.