Patient 1 harbored a homozygous nonsense FNIP1 variant (NM_133372.2; c.868C > T), patient 2, a homozygous splice site variant (c.3306 + 1G > A), and patient 3, a large deletion in exons 9 to 18 and a paternally inherited single-nucleotide variant (c.3218delT; p. Leu1073Wfs*32) causing agammaglobulinemia, neutropenia, recurrent infections along with HCM, renal cysts, and neurological disabilities. This evidence concerns the gene FNIP1 and agammaglobulinemia.