Among 9 underweight patients from PID group (ages 3–18), 4 people had been diagnosed with ataxia-telangiectasia, 2 with Nijmegen breakage syndrome, 1 with Edwards syndrome, 1 with main classes immunoglobulin deficiency and 1 with C-1 esterase inhibitor and partial C4 component deficiency. This evidence concerns the gene C4A and Nijmegen breakage syndrome.