GPT and obesity due to melanocortin 4 receptor deficiency: When data from controls and individuals with obesity were taken together, circulating GDF15 levels were found to positively correlate with several factors related to glucose metabolism (glucose, insulin, C-peptide, HbA1c and HOMA-IR), liver health (AST, ALT and GGT), kidney health (urea, creatinine and uric acid) and inflammatory markers (CRP).