Thymic hypoplasia and T-cell deficiency in ectodermal dysplasia: case report and review of the literature.

Ectodermal dysplasia is a heterogeneous disorder that includes a constellation of congenital malformations occasionally associated with mild to moderate immune dysfunction. In this report, we describe a female infant with ectodermal dysplasia who was found to have thymic hypoplasia but no other phenotypic features of the DiGeorge anomalad. She experienced Candida parapsilosis sepsis at 1 week of age and a skin infection with Mycobacterium chelonii at 6 months. The numbers of blood B cells were normal and serum immunoglobulins normal to slightly reduced, but serum antibody responses of all immunoglobulin isotypes to protein immunogens were absent. Blood T cells were profoundly reduced and proliferative responses of T cells to mitogens were blunted. In contrast, there was an increased number of natural killer (NK) cells and increased NK activity in the blood. Over the first year of life, some of the immunodeficiencies resolved. Although the numbers of blood T cells (17% of total lymphocytes) remained low, proliferative responses to mitogens normalized and specific antibody responses improved. It seems likely that the thymic hypoplasia in this case was due to a paucity of ectodermal elements in the developing thymus, and that the immune defects were largely secondary to that event. In that respect, this human model of ectodermal dysplasia and thymic hypoplasia resembled the ectodermal/thymic defects found in the nude mouse.