Mutation analysis. (A) Mutations in ITGB2 patients with LAD-1. The 4 mutations in these 3 patients all affect the highly conserved I/A domain of the protein. The numbering of the mutated residues is calculated from the beginning of the signal sequence. (B) Comparison of sequences. CD3⁺/CD18⁺ and CD3⁺/CD18⁻ cells from 3 LAD-1 patients were sorted and genomic DNA was extracted. Mutation sites and surrounding sequence were PCR amplified and subcloned. Clones were sequenced and compared for each patient. All of the 20 CD18⁺ clones screened for patient 3 had wt intronic sequence. The mutation A>G at nt 1052 was maintained (not shown).