TBX20 and familial dilated cardiomyopathy: The observation that the TBX20F256I mutation leads to a decreased association with CASZ1, along with the finding that patients heterozygous for a predicted TBX20 null mutation (TBX20Q195X) [23] also display DCM suggest that the TBX20F256I mutation may be acting in a haploinsufficient fashion.