SHOX2 and cardiac arrhythmia: The mortalityrate can be mitigated with closely related hypomorphic Shox allelereplacing Shox2, however the arrhythmias persist [19, 58].Early in embryonic cardiac development, Shox2 isexpressed in the SAN, right venous valve, and dorsalmesenchymal protrusion of the heart [19, 40].