CLK1 and obesity due to melanocortin 4 receptor deficiency: On the contrary, consistent with previous studies showing that ClockΔ19/Δ19 homozygous mutant mice (denoted as Clk/Clk) exhibit propensity for metabolic dysfunctions such as obesity and hyperglycemia18, 19, we also observed metabolic dysfunctions in Clk/Clk (Supplementary Fig. 3).