Similarly, of the patients with severe anaemia and HIV in the study in Cape Town, 59% were females.18 The sex and age distribution reflects that of persons with HIV in the South African population where there is a higher overall HIV prevalence in females of 14.4% compared with 9.9% in males, and the proportion of persons aged 15–49 years is 90% (of those aged 15 years or more).22 Most patients had advanced HIV disease as indicated by a high viral load and a mean CD4 less than 200, a level below which there is a high risk of severe opportunistic infections and HIV-related cancers. The gene discussed is CD4; the disease is anemia (phenotype).