KL and osteoporosis: Mutant mice homozygous for a severely downregulated hypomorphic allele of the α-klotho gene (referred to as klkl/kl or klotho mice) manifest multiple age-related disorders that are also observed in humans, including infertility, growth retardation, osteoporosis, pulmonary emphysema, skin atrophy, ectopic calcification and shortened lifespan20.