A spectrum of mutations in SH2D1A that causes X-linked lymphoproliferative disease and other Epstein-Barr virus-associated illnesses

X-linked lymphoproliferative disease (Duncan's Disease) was first encountered by David T. Purtilo in 1969. The first communication describing the disease was published in 1975. In 1989 the disease locus was mapped to Xq25. Ten years later the gene (SH2D1A. SAP, DSHP), which is absent or mutated in XLP patients was identified. Since that the protein crystal structure of this small, SH2-domain containing protein has been solved, target molecules of the protein have been identified, physiological and pathological protein/protein interactions have been characterized, and the mouse model of the gene mutation has been developed. That said, a complete understanding of the function of the normal SH2D1A protein in immunoregulation and of the altered immune responses in XLP patients is not yet at hand. Therein lies the legacy of Purtilo's discovery for, as with other primary immunodeficiencies, these experiments of nature offer a window or the beauty of the immune system. In due course, the manner by which this gene orchestrates an elegant response (akin to a Mozart divertimento) to EBV infection shall be defined. When something in the world appears absurd, ridiculous or evil, it can be so because of our imperfect knowledge and our desire to see things arranged to suit our own tastes. But if we regard the world from the standpoint of eternal order, we realize that things seem evil merely because we lack knowledge and wisdom.