As expected, the highest number of genetic defects were found in genes underlying the most frequent “classical” PID: mutations in SERPING1 were found in 178 of 341 HAE cases (52.2%), WAS in 154 (100%) of WAS patients, BTK in 114 of 155 X-LA (73.5%), CYBB in 98 (73%) of CGD 135 cases, NBN in 75/88 (85%) of NBS patients and ATM in 55/127 (43%) of AT patients. The gene discussed is ATM; the disease is ataxia telangiectasia.