CD4 and mitochondrial DNA depletion syndrome 4a: The World Health Organization (WHO) defines AHD in adults, adolescents, and children older than five years as having a CD4 cell count < 200cells/mm.3 or stage 3 or 4, including both ART naïve individuals and those who interrupt treatment and return to care; all children younger than five years with HIV are considered as having AHD [2].