Nucleotide substitutions (CT to GA) result in the creation of a premature stop codon (p.S345*) and the truncation of the last 15 residues of the C-terminal domain. This mutation has been identified in patients with warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome. In addition to this exon 2 mutation, a loxP site flanked neomycin resistance gene cassette was inserted into intron 2. The neo cassette was subsequently removed through cre-mediated recombination. (J:178789, J:186735)