P3 developed lymphopenia during his third decade of life, with a count of total lymphocytes of 924 ± 266 cells/mmc (media ± SD), CD4 + T cells of 339 ± 94 cells/mmc (media ± SD), CD8 + T cells of 205 ± 59 cells/mmc (media ± SD), and NK cells deficiency of17 ± 7 cells/mmc (media ± SD). The gene discussed is CD4; the disease is lymphopenia.