KL and cardiac hypertrophy: Because genetic disruption of vitamin D signalling rescues the lethal phenotype of Fgf23 and Klotho null mice26, 27, we used Fgf23−/−/VDRΔ/Δ and Klotho−/−/VDRΔ/Δ compound mutants to assess the role of Fgf23 and Klotho in the pathophysiology of cardiac hypertrophy.