Sib understanding of genetics and attitudes toward carrier testing for X-linked severe combined immunodeficiency.

X-linked severe combined immunodeficiency (XSCID) is the most common genetic form of SCID, a rare disease with profoundly impaired immunity. SCID was previously fatal but now can be treated by bone marrow transplantation. Mapping of XSCID in 1985 and identification of the disease gene, IL2RG, in 1993 made possible patient and carrier diagnosis. We assessed understanding of the genetics of XSCID in adult sibs recruited from families in which a proband had enrolled in our protocols and had attended an XSCID family workshop. Thirty-seven female and three male sibs completed a questionnaire and semistructured interview. Overall knowledge of genetics of XSCID was excellent. An overwhelming majority of participants (93%) believed that daughters should be tested for XSCID carrier status; 89% would prefer to have their own daughter tested prior to age 18 years (M = 9, median = 12), and 34% would test at birth. Moreover, 89% felt they would disclose carrier results to their daughter before adulthood (M = 12 years, median = 12); 51% would tell prior to adolescence. XSCID sibs were optimistic about medical science and assertive in their search for the latest information. Genetic information should be made available to families over time and should include discussion of reproductive risks for sons surviving with XSCID and daughters as they grow up. We recommend that genetic counseling for XSCID include children in age-appropriate discussions and that counselors help parents weigh benefits of early testing and disclosure versus the potential harm of loss of child autonomy.