For instance, not all studies identified elevated expression of RBP4 in adipose tissue of obese patients (Janke et al., 2006), and instead of adipose tissue expression, kidney function was proposed as major determinant of its serum levels, which is known to deteriorate upon the onset of type 2 diabetes and thus may lead to an accumulation of RBP4 in the blood (Raila et al., 2007; Henze et al., 2008). Here, RBP4 is linked to type 2 diabetes mellitus.