Hyper IgM Syndrome is an immune disorder usually caused by an X-linked mutation in the CD40L(CD154) gene. In this study, the authors were able to discern an altered CD40L phenotype in a patient. While anti-CD40L mAbs still recognized the molecule in flow cytometry, a recombinant CD40 reagent failed to bind. Genetic analysis determined this to be caused by a missense variant mutation in the CD40L gene: p.Arg203Ile.
