They present thymic hypoplasia and hypofunction, B and T cell lymphopenia, an inverted CD4/CD8 T cell ratio (with increased proportion of CD8+ and reduction of CD4+ T lymphocytes), impaired function of neutrophils, B, T, and NK cells, post-thymic lymphocyte maturation defects, chemotactic and phagocytic abnormalities, aberrations in humoral immunity and altered levels of total immunoglobulins and their subclasses (Nižetić and Groet, 2012; Satgé and Seidel, 2018; Araya et al., 2019). The gene discussed is CD4; the disease is lymphopenia.