CPT1B and obesity due to melanocortin 4 receptor deficiency: Robitaille et al. found a significant association between the heterozygous E531K allelic variant genotype, which replaces glutamic acid (E) for lysine (K) at position 531 of muscle-type CPT1 (CPT1B), and indicators of obesity when the proportion of dietary fat was ≥34.4%, indicating a gene–diet interaction [11].