Noticeably, polyautoimmunity was also noted in children affected with other forms of IEI paralleled with the hyper-IgM (HIGM) phenotype, e.g., class-switch recombination defects due to genetic variants in the IKBKG gene, aka NEMO, regulating the activity of nuclear factor kappa B 1 (NFκB1), and subsequent deregulation of activation-induced cytidine deaminase (AID) and uracil DNA glycosylase (UNG) enzymatic activity [26], as well as HIGM manifestation of ataxia-telangiectasia [27,28]. The gene discussed is UNG; the disease is Ataxia-telangiectasia.