GHRL and obesity due to melanocortin 4 receptor deficiency: Obesity is a major risk factor for OSA at all ages and OSA is tightly linked mechanistically to insulin resistance and low-grade inflammation, the drivers of metabolic syndrome.143 Although relatively little is known about the mechanism(s) for the sleep–obesity relationship,144 especially among children, there are reasons to suspect increased stress and altered activity of various hormones, such as leptin, ghrelin, and cortisol.