Elevated IgM levels were also reported in other well-defined immunodeficiencies, such as nuclear factor κB (NF-κB) essential modulator (NEMO), recombination-activating gene (RAG) 2, lipopolysaccharide-responsive beige-like anchor (LRBA), ataxia telangiectasia mutated (ATM), ARTEMIS, and dedicator of cytokinesis (DOCK) 2 deficiency [3,18,19,20,21,22,23]. Here, ATM is linked to Immunodeficiency.