HLA-C and obesity due to melanocortin 4 receptor deficiency: In humans, there are a number of internal or external variables including physical activity (Klitgaard et al., 1990; Minetto et al., 2013; Mosole et al., 2014) or inactivity (Borina et al., 2010), changes in neural stimulus (Mu et al., 2012), aging (Klitgaard et al., 1990; Vandervoort, 2002; D'Antona et al., 2003; Short et al., 2005; Mosole et al., 2014), and diet or obesity (Krotkiewski and Björntorp, 1986; Lillioja et al., 1987; Hickey et al., 1995; Kriketos et al., 1996; Tanner et al., 2002; Matsakas and Patel, 2009) that can influence MHC isoform expression.