CD4 and Menkes disease: During MD progression, no significant methylation changes of CD4 promoter were detected in L63 chickens at 5, 10 and 21 dpi or in L72 chickens at 5 and 10 dpi (P>0.05, Figure 1, and Figure 1A and 1B); however, the significant down-regulation of CD4 promoter methylation level was observed at 21 dpi in L72 chickens (P< 0.05, Figure 1C).