Twenty-six cases of PID with PML have been reported, of which some, such as STAT1 gain of function (GOF), Wiskott–Aldrich syndrome, and DOCK8 deficiency, have been reported in more than one patient, but disorders such as X-linked agammaglobulinemia, CD40 ligand (CD40L) deficiency, purine nucleoside phosphorylase (PNP) deficiency, adenosine deaminase (ADA) deficiency, and immunodeficiency-centromeric instability-facial anomalies syndrome (ICF syndrome), were found in only a single case [5]. The gene discussed is ADA; the disease is purine nucleoside phosphorylase deficiency.