Mutational analysis ofSH2D1AmRNA from the patients with XLP. Direct sequencing of the RT-PCR products was performed with the same primer pairs used for PCR amplification. The amplified fragment from patient 1 totally lacked exon 2. Data for patient 2 showed the same 102C>A missense mutation as in the genomic mutational analysis. Of the 2 different size-amplified fragments from patient 4, the longer fragment had no mutations (data not shown). The shorter fragment lacked exon 2 entirely and the first 55 nucleotides of exon 3.