HIF3A and obesity due to melanocortin 4 receptor deficiency: A recent study by Richmond et al. [30] combined several of these methods to investigate causality between BMI and methylation at HIF3A (a gene linked to metabolism and obesity, and associated with adiposity in multiple EWAS [31, 32]), including bidirectional Mendelian randomisation analysis, longitudinal analysis of HIF3A methylation, and analysis of association between maternal pregnancy BMI and HIF3A methylation in offspring at birth (using cord blood).