novel cd40lg mutation in two cousins with immunoglobulin class switch recombinant deficiency

The hyper-immunoglobulin m (higm) syndrome comprises a group of rare inherited immunodeficiency disorders characterized by normal or elevated levels of serum igm with low or absent levels of serum igg, iga, and ige. patients with this syndrome usually present with a history of recurrent infections or opportunistic infections. here, we report two male cousins from homozygote twin mothers. the first cousin presented with no signs or symptoms other than neutropenia, which was accidentally found in a routine blood test. immunological workup in this patient showed undetectable igg and iga levels and normal igm levels. the second cousin had a history of recurrent infections, and at the time of admission, he was diagnosed with pneumocystis jirovecii infection. the immunologic workup of this patient showed undetectable igg, decreased iga, and increased igm level. due to their interesting family relationship, genetic analysis was performed, which detected a novel mutation in exon 2 (c.266 del g) of the cd40 ligand gene (cd40lg).