There have been major advances in the understanding of the mechanisms of primary immunodeficiencies (PIDs) during the last decade as a result of the cloning of abnormal genes responsible for the majority of these disorders. These include rare single-gene disorders in which the mutated alleles were discovered by genetic linkage followed by mapping and sequencing of a locus or by testing for mutations in candidate genes that have homologues in rodents suggesting likely targets.<sup>53 Ochs H., Smith C.I.E., Puck J. Primary Immunodeficiency Diseases: A Molecular and Genetic Approach  : Oxford University Press (1999). 

Cliccare qui per andare alla sezione Riferimenti</sup> Common variable immunodeficiency (CVID), the most prevalent of the PIDs, remains an enigma, and it will take years to develop a clear understanding of this disorder. One major problem when investigating cohorts of patients with CVID is knowing whether they have the same disease or different diseases with a similar clinical phenotype. It is likely that much of the literature on the mechanisms of CVID is tarnished by the inclusion of a few patients with late presentation of a single gene disorder characterized by hypoimmunoglobulinemia (e.g., X-linked agammaglobulinemia [XLA], X-linked hyper-IgM [X-HIM] syndrome). Nevertheless, a substantial proportion of patients diagnosed with CVID have a clinically definable, genetically based condition.