WHIM syndrome is an extremely rare combined immunodeficiency disorder caused predominantly by heterozygous nonsense and missense mutations in the cytoplasmic tail of CXCR4, the most common being the replacement of Arginine 334 by a stop codon, which deletes the last 19 amino acids of the C-terminus domain (140, 141). The gene discussed is CXCR4; the disease is WHIM syndrome.