We could only assume that her deceased sibling (subject II-1) who exhibited a similar phenotype including profound agammaglobulinemia and severe cardiac involvement, eventually succumbing of cardiogenic shock, very likely harbored an identical genetic variant in FNIP1. A healthy mother (subject I-2) was found to harbor a heterozygous mutation. The gene discussed is FNIP1; the disease is agammaglobulinemia.