β-Klotho gene variation is associated with liver damage in children with NAFLD.

•The KLB rs17618244 variant increases the risk of ballooning and lobular inflammation in children with NAFLD.•KLB plasma levels are lower in carriers of the rs17618244 minor A allele.•KLB plasma levels are associated with lobular inflammation, ballooning and fibrosis.•KLB mutant induces intracellular lipid accumulation in HepG2 and Huh7.•KLB mutant causes upregulation of lipotoxic and proinflammatory genes.