For example, in a cross-sectional analysis of a U.S. representative sample from NHANES 1999–2000 and 2003–2004, higher serum PFNA was associated with hyperglycemia but with lower risk of metabolic syndrome, while PFOA was associated with higher β-cell function, and PFOS was associated with higher insulin, HOMA–IR, and β-cell function [220]. This evidence concerns the gene INS and metabolic syndrome.