Researchers continue to investigate the klotho gene and the effects it may have on human longevity: "In mice a defect of Klotho gene expression results in multiple aging-like phenotypes including short lifespan, osteoporosis and atherosclerosis, while its over-expression suppresses aging and extends lifespan. Contrasting data have been reported as far as the importance of the functional variant of Klotho termed "KL-VS" on human longevity, depending on the average age of the old subjects that were compared with young controls. We therefore performed a study on a large Italian population sample including people from very young to very old age (centenarians). ... found a significant increase of the heterozygous Klotho genotype in the class of elderly [non-centenarian] people compared to young controls. On the contrary, no difference was present between centenarians and young controls. [This is] is compatible with the hypothesis that this KL-VS heterozygous genotype is favorable for survival in old people, its beneficial effect decreasing thereafter. ... alleles and genotypes involved in aging and longevity may exert their biological effect at specific time windows." So evidence suggests one klotho variant helps humans survive into old age, but don't help us make it to extreme old age - which raises more questions as to the underlying mechanisms.