ATP2A1 and myotonic dystrophy type 1: In vertebrate systems, differential isoform regulation through development has long been appreciated, and in some disease states such as type 1 myotonic dystrophy, fetal or neonatal stage isoforms of Tnnt2, Atp2a1 (Serca1), and Ldb3 (Zasp) are inappropriately expressed [10–12].