Hypomorphic RAG deficiency: impact of disease burden on survival and thymic recovery argues for early diagnosis and HSCT.

Patients with hypomorphic mutations in the RAG1 or RAG2 gene present with either Omenn syndrome or atypical combined immunodeficiency with a wide phenotypic range. Hematopoietic stem cell transplantation (HSCT) is potentially curative, but data are scarce. We report on a worldwide cohort of 60 patients with hypomorphic RAG variants who underwent HSCT, 78% of whom experienced infections (29% active at HSCT), 72% had autoimmunity, and 18% had granulomas pretransplant. These complications are frequently associated with organ damage. Eight individuals (13%) were diagnosed by newborn screening or family history. HSCT was performed at a median of 3.4 years (range 0.3-42.9 years) from matched unrelated donors, matched sibling or matched family donors, or mismatched donors in 48%, 22%, and 30% of the patients, respectively. Grafts were T-cell depleted in 15 cases (25%). Overall survival at 1 and 4 years was 77.5% and 67.5% (median follow-up of 39 months). Infection was the main cause of death. In univariable analysis, active infection, organ damage pre-HSCT, T-cell depletion of the graft, and transplant from a mismatched family donor were predictive of worse outcome, whereas organ damage and T-cell depletion remained significant in multivariable analysis (hazard ratio [HR] = 6.01, HR = 8.46, respectively). All patients diagnosed by newborn screening or family history survived. Cumulative incidences of acute and chronic graft-versus-host disease were 35% and 22%, respectively. Cumulative incidences of new-onset autoimmunity was 15%. Immune reconstitution, particularly recovery of naïve CD4+ T cells, was faster and more robust in patients transplanted before 3.5 years of age, and without organ damage. These findings support the indication for early transplantation.

Spontaneous in vivo reversion to normal of an inherited mutation in a patient with adenosine deaminase deficiency.

Somatic mosaicism in genetic disease generally results from a de novo deleterious mutation during embryogenesis. We now describe a somatic mosaicism due to the unusual mechanism of in vivo reversion to normal of an inherited mutation. The propositus was an adenosine deaminase-deficient (ADA-) child with progressive clinical improvement and unexpectedly mild biochemical and immunologic abnormalities. Mosaicism due to reversion was evidenced by absence of a maternally transmitted deleterious mutation in 13/15 authenticated B cell lines and in 17% of single alleles cloned from blood DNA, despite retention of a maternal 'private' ADA polymorphism linked to the mutation. Establishment of significant somatic mosaicism following reversion to normal could modify any disorder in which revertant cells have a selective advantage.

Antigen presentation to human T lymphocytes. I. Different requirements for stimulation by hapten-modified cells vs. cell sonicates.

We have investigated the cellular and antigenic requirements for incubation of secondary proliferative responses by human T lymphocytes. Two distinct properties of antigen-presenting peripheral blood mononuclear cells were studied: (a) the ability for appropriate cell surface constituents to construct an immunogenic moiety, and (b) the ability to present similar antigenic determinants when they are not covalently bound. Only Ia+ hapten-modified cells were effective stimulators. In contrast, both Ia+ and Ia- cell sonicates could stimulate secondary proliferative responses, but only in the presence of an accessory cell. This accessory cell was present in Ia+ macrophage, but not in Ia+ non-T lymphocyte, preparations. In contrast, macrophages or soluble factors produced by macrophages were not required for primed T cells to undergo hapten-specific proliferation in response to hapten-modified Ia+ stimulator cells. Thus, although all Ia+ cells tested can stimulate primed cells to proliferate, not all Ia+ cells can function as accessory cells for responses to sonicates. This may reflect the unique ability of a subpopulation(s) of Ia+ cells to bind or process sonicates or soluble antigens for appropriate recognition by primed T cells.

Role of Ia-positive cells in induction of secondary human immune responses to haptens in vitro.

We have described techniques for induction of primary and secondary human immune responses in vitro to lymphoid cells modified with trinitrophenyl, dinitrophenyl, and fluorescein isothiocyanate. Optimal secondary proliferative responses required the presentation of hapten on stimulator cells that shared HLA-D region determinants with the responder cell and/or the original stimulator cell. In contrast, hapten-specific cytotoxic responses assessed on modified allogeneic targets with no detected HLA homology with the responder were comparable in magnitude to those detected on modified autologous targets. Furthermore, secondary proliferative, but not cytotoxic, responses required presentation of Ia+ stimulator populations. Modified B cells, surface-immunoglobulin-negative, non T cells (null-cells), and Ia+ activated T cells all induced proliferative responses at least as effectively as equal numbers of hapten-conjugated macrophage/monocytes. Conversely, Ia(-) null cells and macrophages were entirely unable to stimulate. The data thus suggest that for proliferative responses, primed human T cells respond to modified lymphoid cells only when hapten is recognized in the context of Ia molecules.

Carrier detection in X-linked severe combined immunodeficiency based on patterns of X chromosome inactivation.

The X-linked form of severe combined immunodeficiency (XSCID) is underdiagnosed because no methods have been available for detecting carriers. Although boys with XSCID are deficient in T cells, female carriers are immunologically normal. Carriers' normal immune function would be expected if all their T cells were derived from precursors whose X chromosome bearing the XSCID mutation was inactivated early in embryogenesis. Using somatic cell hybridization to separate the active and inactive X chromosomes and restriction fragment length polymorphisms to distinguish them, we have determined the lymphocyte X inactivation pattern in XSCID carriers and their female relatives. In the T cells of three carriers, the X chromosome bearing the XSCID mutation was consistently inactive. Nonrandom X inactivation was also found in the T cells of one at-risk female, while two others had normal, random X inactivation. This method constitutes a generally applicable carrier test for XSCID.

Female germ line mosaicism as the origin of a unique IL-2 receptor gamma-chain mutation causing X-linked severe combined immunodeficiency.

The IL2RG gene encoding the gamma chain of the lymphocyte receptor for IL-2 lies in human Xq13.1 and is mutated in males with X-linked severe combined immunodeficiency (SCID). In a large Canadian pedigree genetic linkage studies demonstrated that the proband's grandmother was the source of an X-linked SCID mutation. However, her T cells did not show the expected skewed X chromosome inactivation pattern of female carriers of SCID, despite her having one affected son and two carrier daughters with skewed X inactivation. Single strand conformation polymorphism analysis of IL2RG in the affected proband was abnormal in exon 5; sequencing revealed a nine nucleotide in-frame duplication insertion. The three duplicated amino acids included the first tryptophan of the "WSXWS" motif found in all members of the cytokine receptor gene superfamily. Mutation detection in the pedigree confirmed that the founder grandmother's somatic cells had only normal IL2RG, and further showed that the SCID-associated X chromosome haplotype was inherited by three daughters, one with a wild type IL2RG gene and two others with the insertional mutation. Female germ line mosaicism is unusual, but its presence in this X-linked SCID family emphasizes the limitations of genetic diagnosis by linkage as compared with direct mutation analysis.

X-linked severe combined immunodeficiency. Diagnosis in males with sporadic severe combined immunodeficiency and clarification of clinical findings.

Over 80% of infants with severe combined immunodeficiency (SCID) of unknown genetic etiology are males, yet less than a third of these affected males have a family history of X-linked disease. To help identify new mutations of the X-linked SCID gene and to provide genetic counseling, X chromosome inactivation patterns in T cells from 16 women who had sons with sporadic SCID were examined. Between 9 and 35 human/hamster hybrids that selectively retained the active human X chromosome were produced from the T cells of each woman and analyzed with an X-linked restriction fragment length polymorphism for which the woman in question was heterozygous. Exclusive use of a single X as the active X was seen in the T cell hybrids from 7 of the 16 women, identifying these women as carriers of X-linked SCID. Studies on additional family members confirmed the mutant nature of the inactive X and revealed the source of the new mutation in three families. To determine whether there were any laboratory characteristics that might differentiate the boys whose mothers were identified as carriers of X-linked SCID from those whose mothers were not, the clinical records of both groups were compared to each other and to a group of 14 boys with a family history of X-linked SCID. The most consistent finding in the 21 patients with X-linked SCID was an elevated proportion of B cells. These data demonstrate the high incidence of spontaneous mutation for the X-linked SCID gene and help clarify the characteristic presenting features of this disorder.

Interleukin-7R alpha mRNA expression increases as stem cells differentiate into T and B lymphocyte progenitors.

The gamma common (gamma c) chain is a partner in several interleukin receptor complexes, including the interleukin-2 receptor (IL-2R), IL-4R, and IL-7R. Mutations in the gamma c gene are associated with X-linked severe combined immunodeficiency (SCID). Using reverse transcriptase-PCR, we examined the level of mRNA-encoding gamma c and its partners in mouse pluripotent hematopoietic stem cells (PHSCs), which repopulate both bone marrow and thymus. We also assayed developing lymphocytes to define which, if any, IL-R complexes are expressed at the earliest stage of T and B lymphocyte maturation. RNA extracted from bone marrow-derived PHSCs did not contain detectable levels of mRNA-encoding IL-7R alpha. However, the most primitive (CD4- CD8-) T cells from the thymus and the most primitive (c-kit+ B220+) B cells from bone marrow contained high levels of IL-7R alpha mRNA. There were no detectable differences between PHSCs and primitive or more mature T and B cells for expression of gamma c mRNA. We conclude that the onset of IL-7R formation occurs at the earliest stage of differentiation of T and B lymphocytes. Our findings are consistent with the hypothesis that the absence of an intact IL-7R (IL-7R alpha and gamma c) may be a critical loss that interrupts lymphopoiesis.

Family pictures: growing up with a brother with X-linked severe combined immunodeficiency.

Severe combined immunodeficiency (SCID) is a rare syndrome of profoundly impaired immunity, most often X-linked (XSCID). In past generations male infants with XSCID succumbed to infections during the first year of life, but prompt diagnosis and bone marrow transplantation currently make survival possible for over 80%. This treatment typically requires hospitalization for several months; thus, the burden on the family is considerable. We assessed the psychological impact on sibs of boys with XSCID. Forty adult sibs from families studied by J.M.P. were interviewed by J.H.F., and rating scales developed. The majority expressed distress over prolonged maternal absence during the affected child's hospitalization; 67% believed the mother had unsuccessfully mourned son(s) who died of XSCID. Half of the sibs reported that communication in the family about XSCID had been poor. Families with a spontaneous mutation were significantly more likely to report separation issues (P = 0.05), perhaps due to stronger maternal guilt. Family communication was significantly related to parental mourning (P = 0.001) and to survivor guilt (P = 0.05). Difficulties for daughters included desire to repair the mother's loss of her own child, as well as attempts to undo feelings of being flawed, by heightened wishes to bear a healthy son. In light of these findings we suggest: 1) bone marrow transplantation and the period of isolation places great stress on the family; parents need help balancing needs of well sibs with needs of the affected son; 2) parents need help with mourning the loss of a son so family secrets will not prevail; and 3) sibs, both bone marrow donors and non-donors, face psychological risks and need support.

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.

Delayed eruption of permanent teeth in hyperimmunoglobulinemia E recurrent infection syndrome.

OBJECTIVE: To determine the incidence of abnormal tooth eruption in patients with hyperimmunoglobulinemia E (hyper-IgE) syndrome. STUDY DESIGN: This study evaluated 34 individuals with hyper-IgE syndrome (age range, 2-40 years). A comprehensive dental history and a head and neck evaluation were performed on all patients. Dental age was assessed in patients younger than 17 years by 2 methods: (1) clinical assessment of tooth eruption and (2) a radiographic method. Relationships between the chronologic age, dental developmental age, and age at tooth eruption were determined. Other oral or dental anomalies were recorded. RESULTS: Of patients older than 7 years, 75% reported problems with permanent tooth eruption, as evidenced by retained primary teeth or the need for elective extractions of primary teeth to allow eruption of permanent teeth. None of the patients experienced problems with eruption of primary teeth. Eruption of the first and second permanent molars also occurred on time. Dental maturity scores were established for 14 patients 17 years of age or younger. In each case, the difference between chronologic age and the estimated dental developmental age was less than 12 months; however, we found a significant discrepancy between the chronologic age and the mean age of tooth eruption in 80% of these patients when using a particular set of standardized values. Persistence of Hertwig's epithelial root sheath was observed on histologic examination. Chronic multifocal oral candidiasis was a consistent feature in patients with hyper-IgE recurrent infection syndrome. Other oral anomalies were also noted. CONCLUSION: We confirmed that a disorder of tooth eruption is part of the hyper-IgE syndrome. This problem occurs because of delayed primary tooth exfoliation rather than a developmental delay in the formation of the permanent dentition. The persistence of Hertwig's epithelial root sheath is unusual and may be associated with the lack of resorption of the primary teeth. Dentists should be aware of this feature of hyper-IgE syndrome because timely intervention will allow normal eruption to occur.

Genetic testing and screening in pediatric populations.

It is conceivable that in the near future a family could present themselves to their health care provider and request to be tested for diseases X, Y, and Z, equipped only with a web page listing of disease-causing genes. The testing of children suggests subtle and controversial inherent conflicts, however. Decisions about whether to provide genetic testing become increasingly murky for a health care professional as the requests advance from testing a child for carrier status for an autosomal recessive disorder, to testing a girl for a sex-linked mutation, to testing an asymptomatic child for a susceptibility to a particular disorder. Although no single case can exemplify every variable and circumstance confronting health care professionals today, this case-based discussion of x-linked severe combined immune deficiency can serve as a framework to examine some of the potential dilemmas surrounding the testing of children for genetic disorders.

Novel intraoral phenotypes in hyperimmunoglobulin-E syndrome.

AIM: Hyperimmunoglobulin-E syndrome (HIES) is a primary immunodeficiency characterized by eczema, recurrent skin and lung infections with pneumatocoele formation, and extremely elevated serum immunoglobulin-E. The precise immunologic defect and genetic etiology remain unknown. Non-immunologic findings include characteristic facial features (prominent forehead, fleshy nasal tip, and increased interalar distance); skeletal involvement (pathological fractures, scoliosis, and craniosynostosis); and retention of primary teeth. This study aims to characterize intraoral soft tissue findings in HIES patients. METHODS: Sixty HIES patients (4-54 years, 27 males, 33 females) received intraoral and radiographic evaluations. Chronological dental development was also assessed. RESULTS: Lesions of the hard palate and dorsal tongue were found in 55% and 60% of patients, respectively. Palatal lesions ranged from a generalized surface keratosis to a midline sagittal fibrotic bridge. Tongue lesions consisted of multiple fissures and a midline cleft. On the lip and buccal mucosa, keratotic plaques and/or surface fissures were found in 8% and 23% of patients, respectively. Manifested in 76.7% of patients, the intraoral lesions were significantly more prevalent than the characteristic facial traits (P=0.0013). CONCLUSIONS: Alterations in oral mucosa and gingiva were present in the majority of HIES patients. These novel intraoral findings may facilitate the diagnosis of HIES.

Molecular basis for three X-linked immune disorders.

Gene defects causing three X-linked human immunodeficiencies, agammaglobulinemia (XLA), hyper-IgM syndrome (HIGM), and X-linked severe combined immunodeficiency (SCID), have been identified. These represent the first human disease phenotypes associated with three gene families already recognized to be important in lymphocyte development and signaling: XLA is caused by mutations of a B-cell specific intracellular tyrosine kinase; HIGM by mutations in the tumor necrosis factor-related CD40 ligand, through which T cells deliver helper signals by direct contact with B-cell CD40; and SCID by mutations in the gamma chain of the lymphocyte receptor for interleukin-2. The great variety of patient mutations in all three genes represent both a challenge for genetic diagnosis and a resource for dissecting molecular domains and physiologic functions of the gene products.

Molecular and genetic basis of X-linked immunodeficiency disorders.

Within a short time interval the specific gene defects causing three X-linked human immunodeficiencies, agammaglobulinemia (XLA), hyper-IgM syndrome (HIGM), and severe combined immunodeficiency (XSCID), have been identified. These represent the first human disease phenotypes associated with each of three gene families already recognized to be important in lymphocyte development and signaling: XLA is caused by mutations of a B cell-specific intracellular tyrosine kinase; HIGM, by mutations in the TNF-related CD40 ligand, through which T cells deliver helper signals by direct contact with B cell CD40; and XSCID, by mutations in the gamma chain of the lymphocyte receptor for IL-2. Each patient mutation analyzed to date has been unique, representing both a challenge for genetic diagnosis and management and an important resource for dissecting molecular domains and understanding the physiologic function of the gene products.

Primary immunodeficiency diseases.

Primary immunodeficiencies are rare, but important for 3 reasons. First, a high index of suspicion and prompt diagnosis can lead to lifesaving treatment or significant improvement in quality of life. Second, appreciation of the genetic nature of a host defense defect makes possible family counseling and carrier and prenatal diagnosis. Finally, the large and growing list of human genetic defects in immune pathways provides an important tool for understanding human immunoregulation. Many inherited immunodeficiency diseases have had their genetic cause proven with the discovery of their disease genes within the past 5 years. These diseases provide a framework into which additional diseases and disease gene discoveries can be added as the rapid progress in molecular immunology and genetics continues.

Prenatal diagnosis and genetic analysis of X-linked immunodeficiency disorders.

Several congenital immunodeficiency diseases can exhibit X-linked inheritance, including agammaglobulinemia, severe combined immunodeficiency, Wiskott-Aldrich syndrome, X-linked lymphoproliferative syndrome, and X-linked hyper-IgM syndrome. To date, the gene defects causing each of these X-linked immunodeficiencies have not been identified, and the pathogenic mechanisms whereby mutations in these genes result in immunodeficiency are obscure. Although rare, all are associated with severe infections from early life and high morbidity and mortality. Regional localization of each of these gene defects on the X chromosome has made possible carrier detection and prenatal diagnosis by linkage with polymorphic X chromosome markers in pedigrees demonstrating clear X-linked recessive inheritance. However, without a positive family history, it may not be possible to distinguish clinically between X-linked and autosomal forms. As a partial solution to this problem, it has now been established that female carriers of X-linked agammaglobulinemia, X-severe combined immunodeficiency, and Wiskott-Aldrich syndrome can be identified by the pattern of X chromosome inactivation in cell lineages targeted by each gene defect. As more families are offered the opportunity to use carrier detection and prenatal diagnosis, their decisions will reflect not only their personal experience with affected children with immunodeficiency, but also the clinical advances in bone marrow transplantation and immunomodulation.