For example, in severe combined immunodeficiency (SCID) humans lacking functional T, B, and NK cells due to adenosine deaminase (ADA) deficiency or an IL-2 common receptor gamma chain (IL2γc) mutation (atypical X-linked SCID), opportunistic fungal infections are commonly seen in early life (Fischer, 2000; Kumrah et al., 2020). The gene discussed is ADA; the disease is severe combined immunodeficiency.