Israel Medical Association Journal

Inborn errors of immunity represent a heterogeneous group of disorders with variable clinical manifestations. Within this group of disorders, severe combined immunodeficiency (SCID) is the most profound disorder, where affected infants present clinically early in life, and have almost uniformly fatal outcome unless hematopoietic stem cell transplantation (HSCT) is performed. Gene therapy or enzyme replacement therapy are options in some specific SCID forms [1]. The estimated incidence of SCID in the United States is 1 in 58,000 live births, while in Israel the incidence is as high as 1 in 29,000 live births. This higher rate is due to a high rate of consanguineous marriages in certain communities [2].

Severe combined immunodeficiencies represent a heterogeneous group of hereditary defects of the immune system that affect both T and B cells and whose etiology has only recently begun to be understood. A portion of these SCID patients bear a defect in either of the two recombination-activating genes, Rag-1 or Rag-2, while others have mutations in a newly identified gene, Artemis. Omenn syndrome is an unusual severe immunodeficiency with T cells but no B cells, and peculiar features also due to a defect in Rag-1 or Rag-2 genes. All these three forms are characterized by an impairment of the VDJ recombination, the process that insures the somatic diversification of immunoglobulin and T cell receptor-encoding genes. Recent findings have enabled us to better understand the pathophysiology of these three immunodeficiencies, which affect the V(D)J recombination process to a different extent and in different ways.