NOS2 and Menkes disease: In our previous research, we found that the NOS2 gene, which regulates the generation of NO (nitric oxide) [75], was up-regulated in the non-MHC-associated MD-susceptible chicken lines (L72) [57], which is contrary to the finding in MHC-associated MD-susceptible chicken line (line S13 and line P2a) [76], [77].