Primary T-cell immunodeficiencies.

The phenotypes of many primary T-cell immunodeficiencies have been described, including diseases associated with defective T-cell differentiation and/or activation. Recently, genotypes have been defined for some of them, such as X-linked severe combined immunodeficiency and CD3 deficiencies (or hyper IgM syndrome). Phenotype/genotype correlation studies open a fruitful way to a better understanding of primary T-cell immunodeficiencies.