Embryologic and other developmental considerations of thirty-eight possible variants of the DiGeorge anomaly

Clinical Practice Guidelines for the Immunological Management of Chromosome 22q11.2 Deletion Syndrome and Other Defects in Thymic Development

Current practices vary widely regarding the immunological work-up and management of patients affected with defects in thymic development (DTD), which include chromosome 22q11.2 microdeletion syndrome (22q11.2del) and other causes of DiGeorge syndrome (DGS) and coloboma, heart defect, atresia choanae, retardation of growth and development, genital hypoplasia, ear anomalies/deafness (CHARGE) syndrome. Practice variations affect the initial and subsequent assessment of immune function, the terminology used to describe the condition and immune status, the accepted criteria for recommending live vaccines, and how often follow-up is needed based on the degree of immune compromise. The lack of consensus and widely varying practices highlight the need to establish updated immunological clinical practice guidelines. These guideline recommendations provide a comprehensive review for immunologists and other clinicians who manage immune aspects of this group of disorders.

Autoimmunity in Primary Immunodeficiencies (PID)

Primary immunodeficiency (PID) may impact any component of the immune system. The number of PID and immune dysregulation disorders is growing steadily with advancing genetic detection methods. These expansive recognition methods have changed the way we characterize PID. While PID were once characterized by their susceptibility to infection, the increase in genetic analysis has elucidated the intertwined relationship between PID and non-infectious manifestations including autoimmunity. The defects permitting opportunistic infections to take hold may also lead the way to the development of autoimmune disease. In some cases, it is the non-infectious complications that may be the presenting sign of PID autoimmune diseases, such as autoimmune cytopenia, enteropathy, endocrinopathies, and arthritis among others, have been reported in PID. While autoimmunity may occur with any PID, this review will look at certain immunodeficiencies most often associated with autoimmunity, as well as their diagnosis and management strategies.

[22Q11 microdeletion syndrome: cardiorespiratory symptoms and fibrobronchoscopy]

The 22q11 deletion syndrome is a frequent contiguous-gene deletion syndrome. This disorder has a broad spectrum of phenotypic manifestations. It includes various syndromes such as DiGeorge syndrome. The most frequent clinical manifestations are congenital cardiac defects, characteristic facies, palate malformations, hypoparathyroidism, immunodeficiency due to thymic hypoplasia, growth retardation, and behavioural and psychiatric problems. Among the symptoms observed, many patients suffer from respiratory insufficiency or failure. The origin is often multifactorial. Structural airway abnormalities are frequently found in this syndrome. In many of these patients the malformation is mild or non-existent, and remains asymptomatic. However, in some cases it can cause a severe respiratory insufficiency, being diagnosed when other disorders are ruled out. These cases illustrate the importance of early visualisation of the airway by fibrobronchoscopy in the management of the patient with 22q11 deletion syndrome who has recurrent respiratory difficulties.

Mechanisms of tolerance to parental parathyroid tissue when combined with human allogeneic thymus transplantation

BACKGROUND

The induction of tolerance toward third-party solid organ grafts with allogeneic thymus tissue transplantation has not been previously demonstrated in human subjects.

OBJECTIVE

Infants with complete DiGeorge anomaly (having neither thymus nor parathyroid function) were studied for conditions and mechanisms required for the development of tolerance to third-party solid organ tissues.

METHODS

Four infants who met the criteria received parental parathyroid with allogeneic thymus transplantation and were studied.

RESULTS

Two of 3 survivors showed function of both grafts but subsequently lost parathyroid function. They demonstrated alloreactivity against the parathyroid donor in mixed lymphocyte cultures. For these 2 recipients, parathyroid donor HLA class II alleles were mismatched with the recipient and thymus. MHC class II tetramers confirmed the presence of recipient CD4(+) T cells with specificity toward a mismatched parathyroid donor class II allele. The third survivor has persistent graft function and lacks alloreactivity toward the parathyroid donor. All parathyroid donor class II alleles were shared with either the recipient or the thymus graft, with minor differences between the parathyroid (HLA-DRB1∗1104) and thymus (HLA-DRB1∗1101). Tetramer analyses detected recipient T cells specific for the parathyroid HLA-DRB1∗1104 allele. Alloreactivity toward the parathyroid donor was restored with low doses of IL-2.

CONCLUSION

Tolerance toward parathyroid grafts in combined parental parathyroid and allogeneic thymus transplantation requires matching of thymus tissue to parathyroid HLA class II alleles to promote negative selection and suppression of recipient T cells that have alloreactivity toward the parathyroid grafts. This matching strategy may be applied toward tolerance induction in future combined thymus and solid organ transplantation efforts.

The dynamics of T-cell receptor repertoire diversity following thymus transplantation for DiGeorge anomaly

T cell populations are regulated both by signals specific to the T-cell receptor (TCR) and by signals and resources, such as cytokines and space, that act independently of TCR specificity. Although it has been demonstrated that disruption of either of these pathways has a profound effect on T-cell development, we do not yet have an understanding of the dynamical interactions of these pathways in their joint shaping of the T cell repertoire. Complete DiGeorge Anomaly is a developmental abnormality that results in the failure of the thymus to develop, absence of T cells, and profound immune deficiency. After receiving thymic tissue grafts, patients suffering from DiGeorge anomaly develop T cells derived from their own precursors but matured in the donor tissue. We followed three DiGeorge patients after thymus transplantation to utilize the remarkable opportunity these subjects provide to elucidate human T-cell developmental regulation. Our goal is the determination of the respective roles of TCR-specific vs. TCR-nonspecific regulatory signals in the growth of these emerging T-cell populations. During the course of the study, we measured peripheral blood T-cell concentrations, TCRbeta V gene-segment usage and CDR3-length spectratypes over two years or more for each of the subjects. We find, through statistical analysis based on a novel stochastic population-dynamic T-cell model, that the carrying capacity corresponding to TCR-specific resources is approximately 1000-fold larger than that of TCR-nonspecific resources, implying that the size of the peripheral T-cell pool at steady state is determined almost entirely by TCR-nonspecific mechanisms. Nevertheless, the diversity of the TCR repertoire depends crucially on TCR-specific regulation. The estimated strength of this TCR-specific regulation is sufficient to ensure rapid establishment of TCR repertoire diversity in the early phase of T cell population growth, and to maintain TCR repertoire diversity in the face of substantial clonal expansion-induced perturbation from the steady state.

Longitudinal analysis of immune function in the first 3 years of life in thymectomized neonates during cardiac surgery

The purpose of this study is to evaluate the effects of neonatal thymectomy in the functional capacity of the immune system. We selected a group of 23 subjects, who had undergone thymectomy in their first 30 days of life, during an intervention for congenital heart disease. Several parameters of the immune system were evaluated during their first 3 years of life. Lymphocyte populations and subpopulations (including naive, memory and effector subpopulations), T cell receptor (TCR) Vbeta repertoire, response of T cells following in vitro stimulation by mitogen, quantification of immunoglobulins, TCR excision circles (TRECS) and interleukin (IL)-7 were measured. We found that neonatal thymectomy produces long-term diminution in total lymphocyte counts, especially in naive CD4+ and CD8+ T cells. Additionally, TRECS were decreased, and plasma IL-7 levels increased. A statistically significant negative correlation was found between absolute CD4+ T cells and IL-7 (r = -0.470, P = 0.02). The patients did not suffer more infectious events than healthy control children, but thymectomy in neonates resulted in a significant decrease in T lymphocyte levels and TRECS, consistent with cessation of thymopoiesis. This could produce a compromise in immune function later in life, especially if the patients suffer T cell depletion and need a reconstitution of immune function.

Factors affecting success of thymus transplantation for complete DiGeorge anomaly

Thymus transplantation shows promise for the treatment of athymia in complete DiGeorge anomaly. This report reviews the effects of dose of thymus tissue, ABO compatibility, HLA matching, culture conditions, age of donor and immunosuppression of recipient on immune outcomes at 1 year after transplantation. Forty-nine athymic subjects have been treated with cultured postnatal allogeneic thymus tissue; 36 (73%) survive with only one subject on immunosuppression at 1.5 years. Of 31 surviving subjects more than 1 year after transplantation, 30 (97%) developed naive T cells, T-cell proliferative responses to mitogens and a diverse T-cell receptor beta variable (TCRBV) repertoire. The dose of thymus tissue, HLA matching and use of immunosuppression had nonsignificant effects on these outcome variables. Removal of deoxyguanosine from culture medium and length of culture did not adversely affect outcomes. Use of thymus tissue from donors over 1 month of age, versus under 1 month, resulted in higher total T-cell numbers (p = 0.03). However, this finding must be confirmed in a prospective trial. Although subtle immune effects may yet be associated with some of the factors tested, it is remarkable that consistently good immune outcomes result despite variation in dose, HLA matching and use of immunosuppression.

A case of necrotizing enterocolitis associated with adenovirus infection in a term infant with 22q11 deletion syndrome

Infections with adenoviruses are a common problem in the pediatric population. Normally asymptomatic to mild, those infections tend to take a more severe course in immunocompromised patients. 22q11 deletion syndrome (22q11DS) represents a common genetic disorder causing immunodeficiency from thymic hypoplasia or aplasia, heart defects, a characteristic facial appearance, and velopharyngeal dysfunction. Necrotizing enterocolitis (NEC) is a frequent gastrointestinal emergency observed in neonatal intensive care units. The occurrence of NEC is more prevalent in preterm infants. However, there are cases in term infants, but usually, they are associated with predisposing disorders. In this case report, a child is presented with 22q11DS that postnatally developed NEC associated with an adenoviral infection. Although other viruses such as toroviruses or cytomegaloviruses have been implicated in the pathogenesis of NEC in preterm infants, we could not find any report in the recent medical literature describing an association between adenoviral infections, NEC, and 22q11DS in a term infant.

In vitro human T cell development directed by notch-ligand interactions

Traditionally, the study of human T cell development has relied on the availability of human and mouse thymic tissue. In this chapter, we outline a simple in vitro protocol for generating large numbers of human T-lineage cells from umbilical cord blood (CB)- derived hematopoietic stem cells (HSCs) using a bone marrow stromal cell line. This protocol is broken into three major steps: (1) the maintenance of a working stock of OP9 bone marrow stromal cells expressing the Notch receptor ligand Delta-like 1 (OP9- DL1), (2) the purification of human HSCs from umbilical CB, and (3) the initiation and maintenance/expansion of OP9-DL1 cocultures over time (see Fig. 1). The use of this system opens avenues for basic research as it equips us with a simple in vitro method for studying human T cell development.

Thymus Transplantation

Thymus transplantation was first attempted in the 1960s and 1970s using fetal thymus tissue [1, 2]. The results overall were disappointing [3–6]. In part the poor outcomes related to the lack of reagents needed to characterize and identify the patients into those who were truly athymic (complete DiGeorge anomaly) and those who had bone marrow stem cell problems (severe combined immunodeficiency). It is also possible that the fetal thymus tissue was too small to reconstitute a human infant [7]. The use of fetal thymus carried the risk of fatal graft versus host disease since mature T-cells can be found in the human thymus by the end of the first trimester [3]. By 1986, in a review of 26 infants treated with fetal thymus transplantation, 22 had died; the other 4 patients had achieved a 3-year survival [6].

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Long-term tolerance to allogeneic thymus transplants in complete DiGeorge anomaly

Thymus transplantation in subjects with complete DiGeorge anomaly using postnatal allogeneic HLA-nonmatched cultured thymus tissue provides immunoreconstitution. Tolerance of the newly developed T cells toward the donor thymus has not previously been studied. Mixed lymphocyte cultures were used to test 12 thymus transplant recipients for long-term tolerance toward their thymus allografts. Two subjects tested for responses toward thymus donor peripheral blood mononuclear cells showed significantly less reactivity toward the donors compared to responses against third-party allogeneic cells. Peripheral blood mononuclear cells from 10 other subjects were less responsive toward cryopreserved donor thymic cells than toward allogeneic cells (P=0.00007). Adult control peripheral blood mononuclear cells proliferated strongly in response to the donor thymic cells. Both the subjects and controls showed similar proliferative responses against allogeneic cells and phytohemagglutinin. This study provides in vitro evidence for long-term tolerance of complete DiGeorge anomaly thymus transplantation recipients toward their HLA-nonmatched thymus grafts.

Human T cell reconstitution in DiGeorge syndrome and HIV-1 infection

The thymus is essential for proper development and maintenance of a broad T cell repertoire capable of recognizing a wide-range of foreign antigens. Recent advances in multicolor flow cytometry, non-invasive imaging techniques, and molecular assessments of thymic function have enabled a more comprehensive characterization of human thymic output in clinical settings than in the past. These techniques have been particularly valuable in monitoring human T cells after therapeutic thymic grafting for complete DiGeorge syndrome and during HIV-1 infection and AIDS. By defining the degree and mechanisms of T cell reconstitution in these settings, clinical investigators and primary caregivers have been able to better diagnose, treat and care for individuals with congenital or acquired immune deficiencies associated with loss of thymic function.

Review of 54 patients with complete DiGeorge anomaly enrolled in protocols for thymus transplantation: outcome of 44 consecutive transplants

The purpose of this study was to characterize a large group of infants with complete DiGeorge anomaly and to evaluate the ability of thymus transplantation to reconstitute immune function in these infants. DiGeorge anomaly is characterized by varying defects of the heart, thymus, and parathyroid glands. Complete DiGeorge anomaly refers to the subgroup that is athymic (< 1%). The characteristics of 54 subjects at presentation and results from 44 consecutive thymus transplantations are reported. Remarkably, only 52% had 22q11 hemizygosity and only 57% had congenital heart disease requiring surgery. Thirty-one percent developed an atypical phenotype with rash and lymphadenopathy. To date, 33 of 44 subjects who received a transplant survive (75%) with post-transplantation follow-up as long as 13 years. All deaths occurred within 12 months of transplantation. All 25 subjects who were tested 1 year after transplantation had developed polyclonal T-cell repertoires and proliferative responses to mitogens. Adverse events developing after transplantation included hypothyroidism in 5 subjects and enteritis in 1 subject. In summary, diagnosis of complete DiGeorge anomaly is challenging because of the variability of presentation. Thymus transplantation was well tolerated and resulted in stable immunoreconstitution in these infants.

Placental lesions in a case of DiGeorge sequence

This work describes some placental alterations found in a partial form of DiGeorge sequence, namely, hypoplasia of a cord artery with internal calcification of an extensive endoluminal thrombosis, and widespread calcification of microthrombi in the arteries of the second and third order villous branches. Hypoplasia of a cord artery is a relatively rare event, and is also associated with malformations of the gastroenteric and cardiovascular system, as sometimes described in the DiGeorge sequence. Interesting placental alterations are reported and their likely physiopathologic basis and pathogenic correlation discussed in order to give a better and more comprehensive picture of the DiGeorge sequence in which the correlated placental alterations are not sufficiently known.

Complete DiGeorge anomaly in the absence of neonatal hypocalcemia and velofacial and cardiac defects

We report an atypical case of complete DiGeorge (DG) anomaly that presented initially exclusively as severe combined immunodeficiency (SCID). The child had severe infections at diagnosis, in keeping with the SCID phenotype; however, normal lymphocyte counts and immunoglobulin levels were noted at admission, which delayed diagnosis. Importantly, the child presented without neonatal hypocalcemia or velofacial or cardiac abnormalities at the time of diagnosis, which masked underlying DG. This case outlines the difficulties in making the diagnosis of SCID in a timely manner and illustrates the variation in presentation of the 22q11.2 deletion syndrome. There should be a high index of suspicion for primary immunodeficiency among children with severe infections and, because management may vary, DG anomaly should be considered in the differential diagnosis of T- B+ natural killer+ SCID.

Thymic transplantation for complete DiGeorge syndrome: medical and surgical considerations

BACKGROUND/PURPOSE

Complete DiGeorge syndrome results in the absence of functional T cells. Our program supports the transplantation of allogeneic thymic tissue in infants with DiGeorge syndrome to reconstitute immune function. This study reviews the multidisciplinary care of these complex infants.

METHODS

From 1991 to 2001, the authors evaluated 16 infants with complete DiGeorge syndrome. All infants received multidisciplinary medical and surgical support. Clinical records for the group were reviewed.

RESULTS

Four infants died without receiving a thymic transplantation, and 12 children survived to transplantation. The mean age at time of transplantation was 2.7 months (range, 1.1 to 4.4 months). All 16 infants had significant comorbidity including congenital heart disease (16 of 16), hypocalcemia (14 of 16), gastroesophageal reflux disease or aspiration (13 of 16), CHARGE complex (4 of 16), and other organ involvement (14 of 16). Nontransplant surgical procedures included central line placement (15 of 16), fundoplication or gastrostomy (10 of 16), cardiac repair (10 of 16), bronchoscopy or tracheostomy (6 of 16), and other procedures (12 of 16). Complications were substantial, and 5 of the 12 transplanted infants died of nontransplant-related conditions. All surviving infants have immune reconstitution, with follow-up from 2 to 10 years.

CONCLUSIONS

Although the transplantation of thymic tissue can restore immune function in infants with complete DiGeorge syndrome, these children have substantial comorbidity. Care of these children requires coordinated multidisciplinary support.

Postnatal thymus transplantation with immunosuppression as treatment for DiGeorge syndrome

Complete DiGeorge syndrome is a fatal congenital disorder characterized by athymia, hypoparathyroidism, and heart defects. Less than half of patients are 22q11 hemizygous. The goal of this study was to assess if immune suppression followed by postnatal thymus transplantation would lead to T-cell function in 6 infant patients who had host T cells at the time of transplantation. All infants had fewer than 50 recent thymic emigrants (CD3+CD45RA+CD62L+) per cubic millimeter (mm3) and all had some proliferative response to the mitogen phytohemagglutinin. Four infants had rash, lymphadenopathy, and oligoclonal populations of T cells in the periphery. Five of 6 patients are alive at the follow-up interval of 15 months to 30 months. The 5 surviving patients developed a mean of 983 host CD3+ T cells/mm3 (range, 536/mm3-1574/mm3), a mean of 437 recent thymic emigrants/mm3 (range, 196/mm3-785/mm3), and normal proliferative responses to phytohemaglutinin (follow-up from day 376 to day 873). The TCR repertoire became polyclonal in patients who presented with oligoclonal T cells. All patients had thymopoiesis on allograft biopsy. Postnatal thymus transplantation after treatment with Thymoglobulin shows promise as therapy for infants with complete DiGeorge syndrome who have significant proliferative responses to mitogens or who develop rash, lymphadenopathy, and oligoclonal T cells.

Complete DiGeorge syndrome: Development of rash, lymphadenopathy, and oligoclonal T cells in 5 cases

BACKGROUND

Five patients with DiGeorge syndrome presented with infections, skin rashes, and lymphadenopathy after the newborn period. T-cell counts and function varied greatly in each patient. Initial laboratory testing did not suggest athymia in these patients.

OBJECTIVE

The purpose of this study was to determine whether the patients had significant immunodeficiency.

METHODS

Research testing of peripheral blood included immunoscope evaluation of T-cell receptor beta variable gene segment repertoire diversity, quantification of T-cell receptor rearrangement excision circles, and detection of naive T cells (expressing CD45RA and CD62L).

RESULTS

The patients were classified as having DiGeorge syndrome on the basis of syndromic associations and heart, parathyroid, and immune abnormalities. Immunoscope evaluation revealed that the T-cell repertoires were strikingly oligoclonal in all patients. There were few recent thymic emigrants, as indicated by the very low numbers of naive T cells (<50/mm(3)) and the absence of T-cell receptor rearrangement excision circles. These studies showed that all 5 patients were athymic. Two patients died, one from infection. No thymus was found during the complete autopsy performed on one patient.

CONCLUSION

Patients with DiGeorge syndrome, skin rash, and lymphadenopathy should undergo analysis of naive T-cell numbers and of T-cell receptor beta variability segment repertoire to determine whether they are athymic, even if they have T cells with mitogen responsiveness. It is important for physicians to realize that patients with complete DiGeorge syndrome remain profoundly immunodeficient after development of these atypical features (rash, lymphadenopathy, and oligoclonal T cells). Prompt diagnosis is necessary for appropriate management.

Thymus transplantation in complete DiGeorge syndrome: immunologic and safety evaluations in 12 patients

Complete DiGeorge syndrome is a fatal condition in which infants have no detectable thymus function. The optimal treatment for the immune deficiency of complete DiGeorge syndrome has not been determined. Safety and efficacy of thymus transplantation were evaluated in 12 infants with complete DiGeorge syndrome who had less than 20-fold proliferative responses to phytohemagglutinin. All but one had fewer than 50 T cells/mm3. Allogeneic postnatal cultured thymus tissue was transplanted. T-cell development was followed by flow cytometry, lymphocyte proliferation assays, and T-cell receptor Vbeta (TCRBV) repertoire evaluation. Of the 12 patients, 7 are at home 15 months to 8.5 years after transplantation. All 7 survivors developed T-cell proliferative responses to mitogens of more than 100 000 counts per minute (cpm). By one year after transplantation, 6 of 7 patients developed antigen-specific proliferative responses. The TCRBV repertoire showed initial oligoclonality that progressed to polyclonality within a year. B-cell function developed in all 3 patients tested after 2 years. Deaths were associated with underlying congenital problems. Risk factors for death included tracheostomy, long-term mechanical ventilation, and cytomegalovirus infection. Adverse events in the first 3 months after transplantation included eosinophilia, rash, lymphadenopathy, development of CD4-CD8- peripheral T cells, elevated serum immunoglobulin E (IgE), and possible pulmonary inflammation. Adverse events related to the immune system occurring more than 3 months after transplantation included thrombocytopenia in one patient and hypothyroidism and alopecia in one other patient. Thymic transplantation is efficacious, well tolerated, and should be considered as treatment for infants with complete DiGeorge syndrome.

Transplantation of thymus tissue in complete DiGeorge syndrome

BACKGROUND

The DiGeorge syndrome is a congenital disorder that affects the heart, parathyroid glands, and thymus. In complete DiGeorge syndrome, patients have severely reduced T-cell function.

METHODS

We treated five infants (age, one to four months) with complete DiGeorge syndrome by transplantation of cultured postnatal thymus tissue. Follow-up evaluations included immune phenotyping and proliferative studies of peripheral-blood mononuclear cells plus biopsy of the thymus allograft. Thymic production of new T cells was assessed in peripheral blood by tests for T-cell-receptor recombination excision circles, which are formed from excised DNA during the rearrangement of T-cell-receptor genes.

RESULTS

After the transplantation of thymus tissue, T-cell proliferative responses to mitogens developed in four of the five patients. Two of the patients survived with restoration of immune function; three patients died from infection or abnormalities unrelated to transplantation. Biopsies of grafted thymus in the surviving patients showed normal morphologic features and active T-cell production. In three patients, donor T cells could be detected about four weeks after transplantation, although there was no evidence of graft-versus-host disease on biopsy or at autopsy. In one patient, the T-cell development within the graft was demonstrated to accompany the appearance of recently developed T cells in the periphery and coincided with the onset of normal T-cell function. In one patient, there was evidence of thymus function and CD45RA+CD62L+ T cells more than five years after transplantation.

CONCLUSIONS

In some infants with profound immunodeficiency and complete DiGeorge syndrome, the transplantation of thymus tissue can restore normal immune function. Early thymus transplantation - before the development of infectious complications - may promote successful immune reconstitution.

Thyroid abnormalities as a feature of DiGeorge syndrome: a patient report and review of the literature

DiGeorge syndrome or anomaly consists of a developmental field defect which is characterized by congenital absence or hypoplasia of the thymus and parathyroids, as well as facial dysmorphism and congenital heart defects. Other congenital malformations may coexist, in particular, thyroid abnormalities. A case of congenital hypothyroidism and DiGeorge syndrome is reviewed. Necropsy, clinical, and experimental studies also show that thyroid abnormalities may be a feature of DiGeorge syndrome. Although this could be purely coincidental, our case suggests that thyroid gland dysgenesis may be more common than previously thought. Thus, children with the DiGeorge syndrome may be at higher risk for hypothyroidism. Because of this potential association, patients who are considered to have this anomaly should have early newborn thyroid screening.

Humoral immunity in DiGeorge syndrome

OBJECTIVE

To assess humoral immunity after immunization and natural infection in patients with clinical manifestations of the DiGeorge anomalad.

DESIGN

Retrospective review of cases.

SETTING

Ambulatory immunology clinic of a tertiary care teaching hospital.

PATIENTS

The 13 patients had a symptom complex including congenital heart disease, characteristic facies of the DiGeorge anomalad, possible hypocalcemia, and thymic hypoplasia or aplasia. Molecular and cytogenic studies of 12 patients demonstrated that all had 22q11 microdeletions.

METHODS

Serial studies included lymphocyte population enumeration by flow cytometry, lymphocyte proliferation assays with the mitogens phytohemagglutinin and pokeweed mitogen and Staphylococcus aureus, and immunoglobulin quantitation. Specific antibody studies included virus neutralization assays for poliovirus antibodies, and enzyme-linked immunosorbent assay for diphtheria, tetanus, measles, rubella, varicella-zoster virus (VZV), and cytomegalovirus (CMV) antibodies. Avidity of rubella, VZV, and CMV antibodies was tested by enzyme-linked immunosorbent assay modified to include a mild protein denaturant in the first wash after incubation with sera.

RESULTS

All patients had a CD3+ cell count greater than 0.500 x 10(9)/L and a CD4+ cell count greater than 0.350 x 10(9)/L). One patient had low proliferation responses to S. aureus, and one to phytohemagglutinin and pokeweed mitogen. Immunoglobulin levels, compared with those in age-related control subjects, were normal except that two patients had transient, borderline low IgG levels and two had elevated IgA levels. Specific antibody tests showed (No. of patients with positive results/No. tested) the following: diphtheria (13/13); tetanus (13/13); poliomyelitis caused by polio virus type 1 (5/9), type 2 (9/9), and type 3 (8/9); measles (11/13); rubella (11/13); and infection with VZV (5/5) and CMV (7/13). There were no significant differences in antibody avidity results between patients and control subjects for rubella (mean avidity index, 83.5 +/- 8.79 vs 85 +/- 17.6), VZV (81.6 +/- 3.98 vs 65.1 +/- 12.38), or CMV (69.3 +/- 22.31 vs 73.3 +/- 12.46).

CONCLUSIONS

Patients with "partial" DiGeorge anomalad, defined by clinical and immunologic criteria, can be immunized and for the most part can generate good antibody responses.

Absent aortic and pulmonary valves: investigation of three fetal cases with cystic hygroma and review of the literature

Absent semilunar valve was found in three fetal cases with cystic hygroma. Two cases which simultaneously showed absent aortic and pulmonary valves (AAV and APV, respectively) had double-outlet right ventricle. The third case, which lacked only the aortic valve, had atrioventricular septal defect and anomalous origin of the right subclavian artery. Two of the three cases had a markedly hypoplastic thymus. Fifteen AAV and 179 APV cases, including the above-mentioned cases and others reported elsewhere, were discussed with special reference to the pathogenesis of absent semilunar valve. Of the 15 AAV cases, hypoplasia of the left heart was observed in 11 cases (73.3%), double-outlet right ventricle in 5 (33.3%), and aortic arch malformations in 6 (40.0%). In the 179 APV cases, there were 111 tetralogy of Fallot (62.0%) and 44 right-sided aortic arch (24.6%). DiGeorge anomaly was found in one AAV and eight APV cases. These results indicate a pathogenesis that is possibly related to hemodynamic abnormalities or abnormal neural crest cells. Further investigation will be needed to elucidate a more definite pathogenesis of absent semilunar valve.

Thyroid C cells in the DiGeorge anomaly: a quantitative study

The developmental field defect in the DiGeorge anomaly (DGA) principally affects derivatives of the third and fourth branchial pouches (areas containing a large population of cephalic neural crest cells), including the ultimobranchial body (UB), the reputed source of thyroid calcitonin-producing cells (C cells) in humans. To evaluate the content of C cells in children with DGA, sections of the thyroid in 16 cases of DGA (group I) (8 incomplete and 8 complete forms) and 16 age-matched controls (group II) were stained by immunoperoxidase for calcitonin and chromogranin. Eleven of 16 (69%) cases in group I [4 of 8 (50%) of the complete and 7 of 8 (88%) of of the incomplete cases] and 14 of 16 (88%) of group II exhibited positive-staining cells for both markers, either individually or in small clusters within the follicular epithelial basement membrane. The average number of C cells per high-power field (HPF) (400x) for group I was 1.6 +/- 0.9 and for group II 4.9 +/- 1.7 (P < .005). Although the percentage of positive incomplete DGA cases was the same as that of the control cases, the average number of C cells/HPF was 2.0 +/- 1.1 and similar to that of complete DGA cases (1.2 +/- 0.6). These results demonstrated that C cells are present in the thyroid of patients with DGA more frequently than expected, although in deficient numbers when compared quantitatively to age-matched controls showing a normal infantile pattern of thyroid C cell distribution. Although this observation confirms that there is deficiency of thyroid C cell development in DGA and is in keeping with the assumption that the cells are of neural crest origin, our data raise the possibility of an additional source of C cells, perhaps from thyroid endoderm, in a manner analogous to the endocrine cells of the gut and respiratory tract.

Congenital heart disease in CHARGE association

This study reviews the spectrum of congenital heart disease and associated anomalies in 59 patients with the CHARGE association. We have analyzed our clinical experience in managing the cardiovascular anomalies and have reviewed outcome and risk factors for mortality. This study also highlights problems of cardiac management in children born with multiple system involvement. Twenty patients have died; actuarial survival was 78% at 1 year and 60% at 10 years. In only four of the nonsurvivors could their demise be ascribed to their underlying congenital heart disease. We found the outlook for survival was poor if more than one of the following three features were present; cyanotic cardiac lesions, bilateral posterior choanal atresia, or tracheoesophageal fistula. However, mortality was largely due not to the structural heart or choanal abnormalities, but instead reflected the underlying pharyngeal and laryngeal incoordination which resulted in aspiration of secretions. Furthermore, outcome is likely to be improved if collaboration between specialist surgical teams allows necessary procedures to be performed using the minimum of anesthetics. Examination of both the short- and long-term management of these children has stressed the importance of a multidisciplinary approach to their care. The pattern of cardiac defects was not random; lesions within the Fallot spectrum accounted for 33% of their congenital heart disease. Atrioventricular septal defects were also overrepresented. Not all cardiovascular defects could be explained by hypothesizing a neural crest etiology.