Taken together, our data suggest that the well-established cardiac FGF23/FGFR4 signaling involved in the development of pathologic cardiac hypertrophy with the parallel appearance of cardiac fibrosis is induced in kl/kl mice with high FGF23 levels and klotho deficiency. The gene discussed is FGFR4; the disease is hyperinsulinemic hypoglycemia, familial, 4.