Humoral immunity in DiGeorge syndrome

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.

Plasma cells are essentially absent in the luminal gastrointestinal tract of patients with "complete" 22q11.2 deletion syndrome (DiGeorge syndrome)

Gastrointestinal symptoms are commonly reported in patients with 22q11.2 deletion syndrome or DiGeorge syndrome (DGS) in addition to the dominant cardiac manifestations and immunodeficiency. But literature providing specific morphologic details of the gastrointestinal tract pathology is very limited. Here, we provide the first comprehensive morphologic description of the luminal gastrointestinal tract changes in patients with DGS. Cytogenetically confirmed DGS patients were identified, clinical and laboratory data were reviewed to determine the severity of immunodeficiency, and patients were stratified into mildly immunocompromised, that is, partial DiGeorge anomaly or severely immunosuppressed, that is, complete DiGeorge anomaly groups. Gastrointestinal tract biopsies from these patients were retrospectively reviewed and compared with those from controls without the history of DGS. Patients with immunosuppressed DGS showed a near complete absence of plasma cells in the stomach, duodenum, and colon lamina propria by hematoxylin and eosin evaluation. Immunohistochemistry for CD138 used to highlight plasma cells confirmed this finding. The notable absence of plasma cells adds to the existing knowledge of the pathophysiology underlying DGS and expands the differential diagnostic considerations for this finding, which has been previously described in common variable immunodeficiency. It also provides a useful morphologic marker observable by the readily accessible light microscopy. Second, patients with DGS showed a mild increase in epithelial cell apoptosis in their colon. This finding is significant because of its overlap with morphologic features of gastrointestinal graft versus host disease as thymus transplantation is being used as a treatment option for patients with complete DGS.

Impact of Coronavirus Disease 2019 (COVID-19) on Patients With Congenital Heart Disease Across the Lifespan: The Experience of an Academic Congenital Heart Disease Center in New York City

Background We sought to assess the impact and predictors of coronavirus disease 2019 (COVID-19) infection and severity in a cohort of patients with congenital heart disease (CHD) at a large CHD center in New York City. Methods and Results We performed a retrospective review of all individuals with CHD followed at Columbia University Irving Medical Center who were diagnosed with COVID-19 between March 1, 2020 and July 1, 2020. The primary end point was moderate/severe response to COVID-19 infection defined as (1) death during COVID-19 infection; or (2) need for hospitalization and/or respiratory support secondary to COVID-19 infection. Among 53 COVID-19-positive patients with CHD, 10 (19%) were <18 years of age (median age 34 years of age). Thirty-one (58%) had complex congenital anatomy including 10 (19%) with a Fontan repair. Eight (15%) had a genetic syndrome, 6 (11%) had pulmonary hypertension, and 9 (17%) were obese. Among adults, 18 (41%) were physiologic class C or D. For the entire cohort, 9 (17%) had a moderate/severe infection, including 3 deaths (6%). After correcting for multiple comparisons, the presence of a genetic syndrome (odds ratio [OR], 35.82; P=0.0002), and in adults, physiological Stage C or D (OR, 19.38; P=0.002) were significantly associated with moderate/severe infection. Conclusions At our CHD center, the number of symptomatic patients with COVID-19 was relatively low. Patients with CHD with a genetic syndrome and adults at advanced physiological stage were at highest risk for moderate/severe infection.

Follicular Helper T Cells in DiGeorge Syndrome

DiGeorge syndrome is an immunodeficiency characterized by thymic dysplasia resulting in T cell lymphopenia. Most patients suffer from increased susceptibility to infections and heightened prevalence of autoimmune disorders, such as autoimmune thrombocytopenia. B cells in DiGeorge syndrome show impaired maturation, with low switched-memory B cells and a wide spectrum of antibody deficiencies or dysgammaglobulinemia, presumably due to impaired germinal center responses. We set out to evaluate circulating follicular helper T cells (cTFHs) in DiGeorge syndrome, as markers of T–B interaction in the germinal centers in a cohort of 17 patients with partial DiGeorge and 21 healthy controls of similar age. cTFHs were characterized as CXCR5⁺CD45RA⁻ CD4⁺ T cells using flow cytometry. We verify previous findings that the population of memory CD4⁺ T cells is relatively increased in diGeorge patients, corresponding to low naïve T cells and impaired T cell production in the thymus. The population of CXCR5⁺ memory CD4⁺ T cells (cTFHs) was significantly expanded in patients with DiGeorge syndrome, but only healthy controls and not DiGeorge syndrome patients showed gradual increase of CXCR5 expression on cTFHs with age. We did not observe correlation between cTFHs and serum IgG levels or population of switched memory B cells. There was no difference in cTFH numbers between DiGeorge patients with/without thrombocytopenia and with/without allergy. Interestingly, we show strong decline of PD1 expression on cTFHs in the first 5 years of life in DiGeorge patients and healthy controls, and gradual increase of PD1 and ICOS expression on CD4⁻ T cells in healthy controls later in life. Thus, here, we show that patients with DiGeorge syndrome have elevated numbers of cTFHs, which, however, do not correlate with autoimmunity, allergy, or production of immunoglobulins. This relative expansion of cTFH cells may be a result of impaired T cell development in patients with thymic dysplasia.

Immunodeficiencies Associated with Abnormal Newborn Screening for T Cell and B Cell Lymphopenia

Newborn screening for SCID has revealed the association of low T cells with a number of unexpected syndromes associated with low T cells, some of which were not appreciated to have this feature. This review will discuss diagnostic approaches and the features of some of the syndromes likely to be encountered following newborn screening for immune deficiencies.

Myocardial ischemia/reperfusion injury: the role of adaptor proteins Crk

Recent studies have reported that the ischemia/reperfusion (I/R) myocardium may act as an immune system where an exaggerated inflammatory reaction initiates. With activation of the immune system, damage-associated molecular patterns migrate and adhere into the I/R region and, consequently, induce myocardial injury. Emerging data have indicated that the adaptor proteins Crk are thought to play essential roles in signaling during apoptosis and cell adhesion and migration. Accumulated data highlight that Crk proteins are potential immunotherapeutic targets in immune diseases. However, very few studies have determined the roles of Crk on myocardial I/R injury. This mini review will focus on the emerging roles of Crk adaptors during myocardial I/R injury.

Thymic and bone marrow output in individuals with 22q11.2 deletion syndrome

BACKGROUND

The 22q11.2 deletion syndrome (22q11.2DS) is a congenital multisystem anomaly characterized by typical facial features, palatal anomalies, congenital heart defects, hypocalcemia, immunodeficiency, and cognitive and neuropsychiatric symptoms. The aim of our study was to investigate T- and B-lymphocyte characteristics associated with 22q11.2DS.

METHODS

Seventy-five individuals with 22q11.2DS were tested for T and B lymphocytes by examination of T-cell receptor rearrangement excision circles (TRECs) and B-cell κ-deleting recombination excision circles (KRECs), respectively.

RESULTS

The 22q11.2DS individuals displayed low levels of TRECs, while exhibiting normal levels of KRECs. There was a significant positive correlation between TREC and KREC in the 22q11.2DS group, but not in controls. Both TREC and KREC levels showed a significant decrease with age and only TREC was low in 22q11.2DS individuals with recurrent infections. No difference in TREC levels was found between 22q11.2DS individuals who underwent heart surgery (with or without thymectomy) and those who did not.

CONCLUSION

T-cell immunodeficiency in 22q11.2DS includes low TREC levels, which may contribute to recurrent infections in individuals with this syndrome. A correlation between T- and B-cell abnormalities in 22q11.2DS was identified. The B-cell abnormalities could account for part of the immunological deficiency seen in 22q11.2DS.

The TREC/KREC assay for the diagnosis and monitoring of patients with DiGeorge syndrome

DiGeorge syndrome (DGS) presents with a wide spectrum of thymic pathologies. Nationwide neonatal screening programs of lymphocyte production using T-cell recombination excision circles (TREC) have repeatedly identified patients with DGS. We tested what proportion of DGS patients could be identified at birth by combined TREC and kappa-deleting element recombination circle (KREC) screening. Furthermore, we followed TREC/KREC levels in peripheral blood (PB) to monitor postnatal changes in lymphocyte production.

Methods

TREC/KREC copies were assessed by quantitative PCR (qPCR) and were related to the albumin control gene in dry blood spots (DBSs) from control (n = 56), severe immunodeficiency syndrome (SCID, n = 10) and DGS (n = 13) newborns. PB was evaluated in DGS children (n = 32), in diagnostic samples from SCID babies (n = 5) and in 91 controls.

Results

All but one DGS patient had TREC levels in the normal range at birth, albeit quantitative TREC values were significantly lower in the DGS cohort. One patient had slightly reduced KREC at birth. Postnatal DGS samples revealed reduced TREC numbers in 5 of 32 (16%) patients, whereas KREC copy numbers were similar to controls. Both TREC and KREC levels showed a more pronounced decrease with age in DGS patients than in controls (p<0.0001 for both in a linear model). DGS patients had higher percentages of NK cells at the expense of T cells (p<0.0001). The patients with reduced TREC levels had repeated infections in infancy and developed allergy and/or autoimmunity, but they were not strikingly different from other patients. In 12 DGS patients with paired DBS and blood samples, the TREC/KREC levels were mostly stable or increased and showed similar kinetics in respective patients.

Conclusions

The combined TREC/KREC approach with correction via control gene identified 1 of 13 (8%) of DiGeorge syndrome patients at birth in our cohort. The majority of patients had TREC/KREC levels in the normal range.

Live vaccine use and safety in DiGeorge syndrome

OBJECTIVE

Live vaccines are generally contraindicated in patients with DiGeorge syndrome (DGS), a congenital disorder characterized by cellular immune deficiency. Vaccine utilization and safety in this population are not well described. This study examined vaccination patterns and adverse events following live immunization (AEFLI) in these individuals.

METHODS

A multicenter retrospective cohort study was conducted in subjects with DGS confirmed by fluorescence in situ hybridization assay (chromosome 22q11.2 microdeletion). Live vaccine-preventable illnesses, vaccination coverage and timeliness, and AEFLIs in the 56-day window after live vaccination were examined. Bivariate and multivariable analyses assessed the impact of demographics medical history, timing of diagnostic confirmation, and preceding immune function on vaccination patterns and AEFLIs.

RESULTS

Of 194 subjects, 77% and 75% received measles-mumps-rubella (MMR) and varicella vaccines, respectively; 58% completed recommended vaccinations by age 19 to 35 months. Adverse events occurred after 14% and 20% of MMR and varicella vaccine doses, respectively. Most events were minor, few were serious, and no deaths were reported in post-live vaccination windows. Although early diagnostic confirmation negatively affected live vaccination coverage and timeliness (P < .001), baseline CD4% did not differ between subjects who did or did not receive live vaccines by 12 to 18 months. Among varicella vaccine recipients, those with a subsequent adverse event had a lower preceding CD4% (24.8% ± 7.3%) than those without (35.5% ± 11.7%) (P < .05); no CD4% differences were observed with MMR vaccination. Fourteen unvaccinated subjects experienced live vaccine-preventable illnesses.

CONCLUSIONS

Live vaccines were frequently given and generally well-tolerated among patients with DGS with mild-to-moderate immunosuppression.

Immunodeficiency in DiGeorge Syndrome and Options for Treating Cases with Complete Athymia

The commonest association of thymic stromal deficiency resulting in T-cell immunodeficiency is the DiGeorge syndrome (DGS). This results from abnormal development of the third and fourth pharyngeal arches and is most commonly associated with a microdeletion at chromosome 22q11 though other genetic and non-genetic causes have been described. The immunological competence of affected individuals is highly variable, ranging from normal to a severe combined immunodeficiency when there is complete athymia. In the most severe group, correction of the immunodeficiency can be achieved using thymus allografts which can support thymopoiesis even in the absence of donor-recipient matching at the major histocompatibility loci. This review focuses on the causes of DGS, the immunological features of the disorder, and the approaches to correction of the immunodeficiency including the use of thymus transplantation.

The adaptor protein Crk in immune response

The adaptor proteins Crk (CT10 (chicken tumor virus number 10) regulator of kinase), including CrkI, CrkII and Crk-like, are important signal molecules that regulate a variety of cellular processes. Considerable progress has been made in understanding the roles of the Crk family proteins in signal transduction, with a focus on cellular transformation and differentiation. However, since Crk was identified in 1988, very few studies have addressed how Crk regulates the immune response. Recent work demonstrates that Crk proteins function as critical signal molecules in regulating immune cell functions. Emerging data on the roles of Crk in activation and inhibitory immunoreceptor signaling suggest that Crk proteins are potential immunotherapeutic targets in cancer and infectious diseases. The aim of this review is to summarize recent key findings regarding the role of Crk in immune responses mediated by T, B and natural killer (NK) cells. In particular, the roles of Crk in NK cell functions are discussed.

The diverse clinical features of chromosome 22q11.2 deletion syndrome (DiGeorge syndrome)

A 2-year-old boy with chromosome 22q11.2 deletion syndrome was referred for recurrent sinopulmonary infections. He was diagnosed shortly after birth by a fluorescence in situ hybridization test that was performed due to interrupted aortic arch type B. He had no hypocalcemia, and his recovery from cardiac repair was uneventful. He had difficulty feeding and gained weight slowly, but, otherwise, there were no concerns during his first year of life. At 15 months of age, he began to develop significant otitis media and bronchitis. He was hospitalized once for pneumonia at 18 months of age and has never been off antibiotics for more than 1 week since then. He has not had any previous immunologic evaluation. Recurrent sinopulmonary infections in a child with chromosome 22q11.2 deletion syndrome can have the same etiologies as in any other child. Atopy, anatomic issues, cystic fibrosis, and new environmental exposures could be considered in this setting. Early childhood can be problematic for patients with chromosome 22q11.2 deletion syndrome due to unfavorable drainage of the middle ear and sinuses. Atopy occurs at a higher frequency in 22q11.2 deletion syndrome, and these children also have a higher rate of gastroesophageal reflux and aspiration than the general population. As would be appropriate for any child who presents with recurrent infections at 2 years of age, an immunologic evaluation should be performed. In this review, we will highlight recent findings and new data on the management of children and adults with chromosome 22q11.2 deletion syndrome.

Immunoglobulin deficiencies: the B-lymphocyte side of DiGeorge Syndrome

DiGeorge syndrome is associated with a T-lymphocyte immunodeficiency. The prevalence of hypogammaglobulinemia has not been reported. We found that 3% of patients with DiGeorge syndrome were receiving immunoglobulin replacement therapy and 6% of patients over the age of 3 years had hypogammaglobulinemia. We conclude that DiGeorge syndrome is associated with significant humoral immune deficiency.

Immunological aspects of 22q11.2 deletion syndrome

Chromosome 22q11 deletion is the most common chromosomal deletion syndrome and is found in the majority of patients with DiGeorge syndrome and velo-cardio-facial syndrome. Patients with CHARGE syndrome may share similar features. Cardiac malformations, speech delay, and immunodeficiency are the most common manifestations. The immunological phenotype may vary widely between patients. Severe T lymphocyte immunodeficiency is rare-thymic transplantation offers a new approach to treatment, as well as insights into thymic physiology and central tolerance. Combined partial immunodeficiency is more common, leading to recurrent sinopulmonary infection in early childhood. Autoimmunity is an increasingly recognized complication. New insights into pathophysiology are reviewed.

A prospective study of influenza vaccination and a comparison of immunologic parameters in children and adults with chromosome 22q11.2 deletion syndrome (digeorge syndrome/velocardiofacial syndrome)

Prior to the advent of cardiac bypass, most children with congenital cardiac anomalies and chromosome 22q11.2 deletion syndrome died. With improved technology, there is now a wave of young adults with chromosome 22q11.2 deletion syndrome requiring clinical care. Fifteen young children and 20 adults with chromosome 22q11.2 deletion had flow cytometry, functional T cell analyses, and functional B cell analyses to characterize their immune system. Subjects were vaccinated with the annual inactivated influenza vaccine, and responses were evaluated by hemagglutination inhibition titer assessment. The pattern of T cell subset abnormalities was markedly different between pediatric and adult patients. In spite of the cellular deficits observed in adults, titers produced after influenza vaccine administration were largely intact. We conclude that disruption to T cell production appears to have secondary consequences for T cell differentiation and B cell function although the clinical impact remains to be determined.

Chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion syndrome is a common syndrome also known as DiGeorge syndrome and velocardiofacial syndrome. It occurs in approximately 1:4000 births, and the incidence is increasing due to affected parents bearing their own affected children. The manifestations of this syndrome cross all medical specialties, and care of the children and adults can be complex. Many patients have a mild to moderate immune deficiency, and the majority of patients have a cardiac anomaly. Additional features include renal anomalies, eye anomalies, hypoparathyroidism, skeletal defects, and developmental delay. Each child's needs must be tailored to his or her specific medical problems, and as the child transitions to adulthood, additional issues will arise. A holistic approach, addressing medical and behavioral needs, can be very helpful.

Evans syndrome and antibody deficiency: an atypical presentation of chromosome 22q11.2 deletion syndrome

We report a case of an 8-year-old male patient with Evans syndrome and severe hypogammaglobulinemia, subsequently in whom the 22q11.2 deletion syndrome (22q11.2 DS) was diagnosed. No other clinical sign of 22q11.2 DS was present with the exception of slight facial dysmorphism. The case is of particular interest because it suggests the need to research chromosome 22q11.2 deletion in patients who present with autoimmune cytopenia and peculiar facial abnormalities, which could be an atypical presentation of an incomplete form of 22q11.2 DS.

Secondary immunologic consequences in chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Clinical evidence suggests that patients with Chromosome 22q11.2 deletion (Ch22q11.2D) have an increased prevalence of atopic and autoimmune disease and this has been without explanation. We hypothesized that the increase in atopy was due to homeostatic proliferation of T cells leading to a Th2 skew. We performed intracellular cytokine staining to define Th1/Th2 phenotypes in toddlers (early homeostatic proliferation) and adults (post homeostatic proliferation) with this syndrome. To attempt to understand the predisposition to autoimmunity we performed immunophenotyping analyses to define Th17 cells and B cell subsets. Adult Ch22q11.2D patients had a higher percentage of IL-4+CD4+ T cells than controls. Th17 cells were no different in patients and controls. In addition, adult Ch22q11.2D syndrome patients had significantly lower switched memory B cells, suggesting a dysregulated B cell compartment. These studies demonstrate that the decrement in T cell production has secondary consequences in the immune system, which could mold the patients' clinical picture.

Development of specific T-cell responses to Candida and tetanus antigens in partial DiGeorge syndrome

BACKGROUND

Partial DiGeorge syndrome (pDGS) presents with thymic hypoplasia and a variable decrease in T-cell numbers. Although lymphocyte proliferation to mitogens is generally preserved, it is uncertain whether the development of specific cellular immunity in pDGS is similarly preserved.

OBJECTIVE

We sought to study the development of antigen-specific T-cell responses in patients with pDGS with regard to their initial CD3 T-cell counts.

METHODS

A retrospective review of 93 patients with pDGS followed at Texas Children's Hospital Allergy and Immunology Clinic from 1991 to 2006 was performed. Serial lymphocyte proliferation to Candida and tetanus antigens was longitudinally analyzed. Antigen-specific lymphoproliferation was compared with initial patient CD3 T-cell counts of less than the 10th percentile (n = 63), the 10th to 50th percentile (n = 20), and greater than the 50th percentile (n = 10) of age-matched normal control values. Tetanus-specific IgG levels and the number of tetanus immunizations were also studied.

RESULTS

The median CD3 T-cell counts at baseline in all 3 groups were as follows: 10th percentile, 1188 cells/mm(3) (range, 168-3272 cells/mm(3)); 10th to 50th percentile, 2816 cells/mm(3) (range, 1484-4155 cells/mm(3)); greater than 50th percentile, 4246 cells/mm(3) (range, 2573-6481 cells/mm(3)). Thirty-one (46%) of 68 patients with pDGS who received at least 3 tetanus vaccines had persistent Candida and tetanus-specific cellular immunity, and 24 (35%) did not have immunity to either antigen. Most (22/24) of these patients had CD3 T-cell counts at presentation of less than the 10th percentile of normal values. Protective tetanus-specific IgG titers (>0.10 IU/mL) were detected in all patients tested from the age of 2 to 85 months (n = 72).

CONCLUSION

Some patients with pDGS with low CD3 T-cell counts might not have specific Candida and tetanus cellular immunity.

Chromosome 22q11.2 deletion syndrome: DiGeorge syndrome/velocardiofacial Syndrome

DiGeorge syndrome, or chromosome 22q11.2 deletion syndrome, is a disorder affecting multiple organ systems. The immunologist may be called on to coordinate complex medical care tailored to the specific needs and unique clinical features of each patient. This article focuses on the immune system, but patients require a holistic approach. Attention to cardiac, nutritional, and developmental needs in early infancy is important, and it is critical to identify the rare infants who require either a lymphocyte or thymus transplant. Later, speech and school issues dominate the picture. Allergies and autoimmune disorders also may be troubling for some school-age children.

Immunologic defects in 22q11.2 deletion syndrome

BACKGROUND

22q11.2 Deletion syndrome, the most common congenital chromosome deletion syndrome, is associated with developmental defects including cardiac abnormalities and hypoplasia or abnormal migration of the thymus. These patients have variable defects in T-cell immunity with an increased incidence of infection and autoimmune disease.

OBJECTIVE

To investigate the immunologic constitution of children with 22q11.2 deletion syndrome.

METHODS

We characterized the immunologic constitution of 27 children with 22q11.2 deletion syndrome and 54 healthy controls by flow-cytometric analysis of peripheral blood lymphocyte populations.

RESULTS

Patients exhibited decreased T-cell numbers, although the normal age-related decrease in T-cell numbers was slower than in healthy children. There was a significant decrease in FoxP3(+) natural regulatory T (nTreg) cells with a strong correlation between nTreg cells and recent T-cell emigrants from the thymus, suggesting a link between the nTreg cell population and thymic function. Although total B-cell numbers were unaffected, patients showed a significantly decreased proportion of memory B cells in the B-cell pool.

CONCLUSION

Lower nTreg cells in patients suggest that the generation and maintenance of these cells in children is related to thymic function. In addition to T-cell abnormalities classically seen in this syndrome, subtle defects in the B-cell compartment may also be seen.

Velocardiofacial syndrome, DiGeorge syndrome: the chromosome 22q11.2 deletion syndromes

Velocardiofacial syndrome, DiGeorge syndrome, and some other clinical syndromes have in common a high frequency of hemizygous deletions of chromosome 22q11.2. This deletion syndrome is very common, affecting nearly one in 3000 children. Here, we focus on recent advances in cardiac assessment, speech, immunology, and pathophysiology of velocardiofacial syndrome. The complex medical care of patients needs a multidisciplinary approach, and every patient has his own unique clinical features that need a tailored approach. Patients with chromosome 22q11.2 deletion syndrome might have high level of functioning, but most often need interventions to improve the function of many organ systems.

Immunodeficiency and autoimmunity in 22q11.2 deletion syndrome

22q11.2 deletion syndrome is the commonest chromosome deletion syndrome. 22q11.2 deletion may result in variable clinical phenotypes which may differ even between patients with identical deletions. Abnormal pharyngeal arch development results in defects in the development of the parathyroid glands, thymus and conotruncal region of the heart. Defective thymic development is associated with impaired immune function. 'Complete' DiGeorge syndrome with total absence of the thymus and a severe T-cell immunodeficiency accounts for <0.5% of patients. The majority of patients with 22q11.2 deletion syndromes have 'partial' defects with impaired thymic development rather than complete absence with variable defects in T-cell numbers. Immunodeficiency in these patients is not solely due to T-cell deficiency and abnormalities of T-cell clonality or impairment of proliferative responses may play a role. Humoral deficiencies including defects in the B-cell compartment have also been identified in these patients. 22q11.2 deletion syndrome patients are at increased risk of a variety of autoimmune diseases. A number of immune defects may predispose to the development of autoimmunity in these patients including increased infection, impaired development of natural T-regulatory cells and impaired thymic central tolerance.

Selective IgM deficiency and 22q11.2 deletion syndrome

BACKGROUND

The 22q11.2 deletion syndrome is a common chromosomal disorder with highly variable phenotypic expression and immunologic defects. Humoral immunity is mostly unaffected, but selective IgA deficiency occurs in up to 13% of patients. Selective IgM deficiency associated with 22q11.2 deletion has been reported in 1 patient.

OBJECTIVE

To describe another 2 patients with 22q11.2 deletion syndrome and IgM deficiency.

METHODS

Patient 1 was a 6-year-old boy with recurrent otitis media, sinopulmonary infections, wheezing, and speech delay. His serum IgM level was 18 mg/dL, and his IgA and IgG levels were normal. Antibody titers to protein and carbohydrate antigens were protective. Workup for velopharyngeal insufficiency resulted in the diagnosis of 22q11.2 deletion syndrome 3 years later. Patient 2 was a 14-year-old girl diagnosed as having 22q11.2 deletion at 9 years of age after presenting with neonatal seizures, atrial and ventricular septal defects, recurrent otitis media, mental retardation, and asthma. Her serum IgM level was 11 mg/dL, with normal IgG and IgA levels. Antibody titers to protein and carbohydrate antigens were protective. Patient 3 was a previously described 15-year-old girl with persistently draining ears, 22q11.2 deletion, and an IgM level less than 6 mg/dL. Her clinical and laboratory features are summarized.

RESULTS

Results of further testing on the patients, including lymphocyte enumeration, were normal. The literature is reviewed regarding decreased IgM levels in 22q11.2 deletion syndrome.

CONCLUSIONS

Fluorescence in situ hybridization analysis for chromosome 22q11.2 deletion should be considered in patients with selective IgM deficiency, especially if concurrent chronic otitis media, developmental delay, velopharyngeal insufficiency, or dysmorphic features are present.

DiGeorge Syndrome/Velocardiofacial Syndrome: The Chromosome 22q11.2 Deletion Syndrome

Chromosome 22q11.2 deletion (CH22qD) syndrome is also known as DiGeorge syndrome or velocardiofacial syndrome. This deletion syndrome is extremely common with nearly one in 4000 children being affected. Recent advances and a holistic approach to patients have improved the care and well-being of these patients. This review will summarize advances in understanding the health needs and immune system of patients with CH22qD syndrome. Patients will most often need interventions directed at maximizing function for many organ systems but can ultimately have a high level of functioning.

Humoral immune responses and CD27+ B cells in children with DiGeorge syndrome (22q11.2 deletion syndrome)

The spectrum of T-cell abnormalities in 22q11.2 syndrome is quite broad, ranging from profound and life threatening to non-existent defects. Humoral abnormalities have been described in some of these patients, although no data are currently available on their phenotypical and functional B cell subsets. The purpose of this study was to investigate humoral immune function in a cohort of 13 children with DiGeorge syndrome by immunophenotyping B and by analysing their functionality in vivo. Humoral immunity was assessed by serum immunoglobulin evaluation, IgG subclasses determination, and testing of specific antibody titers to recall antigens. B cells were analyzed by flow cytometry and the relevant percentage of membrane surface expression of CD27, IgM, IgD was evaluated. In our cohort, one of 13 children (7.7%) had a complete IgA deficiency, four of 13 (30.7%) had minor immunoglobulin abnormalities, and five (38%) had an impaired production of specific antibodies. Five of 13 children (38%) had recurrent infections. Interestingly, peripheral CD27+ B cells were reduced in our patients as compared with age-matched healthy controls, and this decrement was statistically significant for IgM+ IgD+ CD27+ B cells. Immunoglobulin abnormalities were associated with the occurrence of recurrent infections. We conclude that a significant proportion of patients with DiGeorge syndrome have defective humoral immunity, which may represent an additional pathogenic mechanism underlying the increased susceptibility to infections. Whether the decreased CD27+ B-cell subset might be one of the defects that contribute to impaired humoral immunity, and to susceptibility to infection remains to be elucidated.

Otolaryngologic manifestations of immunodeficiency

Otolaryngologists are frequently consulted to manage infectious and noninfectious complications of immune deficiency. Although defects of host defense and recurrent or severe infections are the most obvious manifestations of immune deficiency, patients are often at increased risk for autoimmune and malignant disease as well. Knowledge of primary and acquired immune deficiencies will facilitate appropriate identification, treatment, and referral of patients with these defects. When immunodeficiency is known or suspected, it is particularly important to have a high index of suspicion for unusual or severe manifestations of infection, to have a low threshold for obtaining imaging to aid in diagnosis, and to treat infections for longer periods of time with higher doses of antibiotic. Surgery may be required for definitive treatment of infections that do not respond to medical therapy and for management of complications of infectious disease

T-cell homeostasis in humans with thymic hypoplasia due to chromosome 22q11.2 deletion syndrome

Patients with chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome) typically exhibit thymic hypoplasia, conotruncal cardiac defects, and hypoparathyroidism. The immunodeficiency that results from the thymic hypoplasia has been extensively described and consists primarily of T-cell lymphopenia. A curious feature of the T-cell lymphopenia is that the age-related rate of decline of T-cell numbers is slower in patients than controls. This leads to T-cell numbers in adulthood that are minimally decreased compared with controls. This suggests that homeostatic mechanisms might be acting to preserve the peripheral blood T-cell numbers in patients. We characterized changes in CD4/CD45RA and CD4/CD45RO T-cell populations in patients and controls of various ages and determined T-cell recombination excision circles and telomere length within the CD4/CD45RA population. Patients had evidence of accelerated conversion of naive to memory cells and had evidence of more extensive replicative history within the CD4/CD45RA compartment compared with controls. Oligoclonal T-cell receptor (TCR) Vbeta families and missing Vbeta families were seen more often in patients than controls. These data are consistent with homeostatic proliferation of T cells in patients with limited T-cell production due to thymic hypoplasia.

Long-term assessment of T-cell populations in DiGeorge syndrome

BACKGROUND

Patients with DiGeorge syndrome present with a broad range of T-cell deficiency. Partial DiGeorge syndrome (pDGS) is a preferred designation for patients with detectable T-cell function. Among immunology experts, there is no uniform opinion on the necessity of T-cell precautions for pDGS patients. Few studies have addressed the natural course of their immune function over time.

OBJECTIVE

The objective of this study was to describe the natural history of immune parameters in pDGS.

METHODS

We reviewed the medical records of 45 pDGS patients. Peripheral blood T-cell subsets counts and percentages were recorded at 1, 6, 12, 18, 24, 30, 48, 60, 72, 96, and 120 months of age, and the rates of change of T-cell measurements over the follow-up period (slopes) were calculated for each individual. Humoral immunity was evaluated by quantification of immunoglobulins and by testing antibody titers to recall antigens.

RESULTS

T-cell subsets counts from pDGS patients were generally lower than those of age-matched normal populations but were not severely depressed (ie, CD4+ T-cell percentage less than 15%). The median of the slopes for CD3+, CD4+, and CD8+ T-cell percentages were -0.7%, -0.8%, and -0.1%/month, respectively, in the first year of age and 0.1%/month for each subpopulation from 12 to 120 months of age. Lymphoproliferative responses to phytohemagglutinin were adequate at all ages. Immunoglobulin deficiencies or inadequate production of specific antibodies were not detected.

CONCLUSIONS

In our pDGS patient cohort, a significant deterioration of T-cell number or function did not occur over time. Clinical implications of this finding include the possibility of discontinuing T-cell deficiency precautions and frequency of reevaluations of pDGS patients with stable and adequate immune function.

Chromosome 22q11.2 deletion syndrome (DiGeorge and velocardiofacial syndromes)

Chromosome 22q11.2 deletion syndrome occurs in approximately 1 of 3000 children. Clinicians have defined the phenotypic features associated with the syndrome and the past 5 years have seen significant progress in determining the frequency of the deletion in specific populations. As a result, caregivers now have a better appreciation of which patients are at risk for having the deletion. Once identified, patients with the deletion can receive appropriate multidisciplinary care. We describe recent advances in understanding the genetic basis for the syndrome, the clinical manifestations of the syndrome, and new information on autoimmune diseases in this syndrome.

Antibody deficiency and autoimmunity in 22q11.2 deletion syndrome

BACKGROUND

Although severe T cell immunodeficiency in DiGeorge anomaly is rare, previous studies of humoral function in these patients have found no antibody abnormalities but have not examined the response to polysaccharide antigens. Isolated cases of autoimmunity have been reported. Several patients with 22q11.2 deletion attending our immunology clinic suffered recurrent sinopulmonary infection or autoimmune phenomena.

AIMS

To investigate humoral immunodeficiency, particularly pneumococcal polysaccharide antibody deficiency, and autoimmune phenomena in a cohort of patients with 22q11.2 deletion.

METHODS

A history of severe or recurrent infection and autoimmune symptoms were noted. Lymphocyte subsets, immunoglobulins, IgG subclasses, specific vaccine antibodies, and autoantibodies were measured. Subjects were vaccinated with appropriate antigens as indicated.

RESULTS

Of 32 patients identified, 26 (81%) had severe or recurrent infection, of which 13 (50%) had abnormal serum immunoglobulin measurements and 11/20 >/=4 years old (55%) had an abnormal response to pneumococcal polysaccharide. Ten of 30 patients (33%) had autoimmune phenomena; six (20%) were symptomatic.

CONCLUSIONS

Humoral immunodeficiency is more common than previously recognised in patients with 22q11.2 deletion. Normal T cell function and immunoglobulin levels do not exclude poor specific antibody responses. Patients should be referred for formal immunological assessment of cellular and humoral immune function.

Primary cellular immunodeficiencies

Genetic defects in T-cell function lead to susceptibility to infections or to other clinical problems that are more grave than those seen in disorders resulting in antibody deficiency alone. Those affected usually present during infancy with either common or opportunistic infections and rarely survive beyond infancy or childhood. The spectrum of T-cell defects ranges from the syndrome of severe combined immunodeficiency, in which T-cell function is absent, to combined immunodeficiency disorders in which there is some, but not adequate, T-cell function for a normal life span. Recent discoveries of the molecular causes of many of these defects have led to a new understanding of the flawed biology underlying the ever-growing number of defects. Most of these conditions could be diagnosed by means of screening for lymphopenia or for T-cell deficiency in cord blood at birth. Early recognition of those so afflicted is essential to the application of the most appropriate treatments for these conditions at a very early age. The latter treatments include both transplantation and gene therapy in addition to immunoglobulin replacement. Fully defining the molecular defects of such patients is also essential for genetic counseling of family members and prenatal diagnosis.

Immunologic features of chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

OBJECTIVES

To characterize immunologic function and clinical characteristics in patients with chromosome 22q11.2 deletion syndrome and determine whether there was significant change over time.

METHODS

This study characterized the laboratory and clinical features of the immunodeficiency in a cohort of 195 patients with chromosome 22q11.2 deletion syndrome and used cross-sectional and analysis of variance to compare the findings in different age groups with control patients. Changes over time were also characterized by a model effect method in a subset of patients who were studied serially.

RESULTS

Diminished T cell counts in the peripheral blood are common in patients with chromosome 22q11.2 deletion syndrome. The pattern of changes seen with aging in normal control patients was also seen in patients with chromosome 22q11.2 deletion syndrome, although the decline in T cells was blunted. Autoimmune disease was seen in most age groups, although the types of disorders varied according to age. Infections were also common in older patients, though they were seldom life threatening.

CONCLUSIONS

Slow declines in T cell populations are seen in chromosome 22q11.2 deletion syndrome. Clinical manifestations of immunodeficiency, such as recurrent infection and autoimmune disease, were common in this population but had little relationship to specific immunologic laboratory features.

22q11.2 deletion syndrome: DiGeorge, velocardiofacial, and conotruncal anomaly face syndromes

A microdeletion of chromosome 22q11.2 is found in most patients with velocardiofacial syndrome, DiGeorge syndrome, and conotruncal anomaly face syndrome, and in some patients with Cayler cardiofacial and autosomal dominant Opitz-G/BBB syndromes. A wide spectrum of clinical findings accompanies the 22q11.2 deletion, without genotype or phenotype correlation even among affected family members. Classic features are dysmorphic facies, conotruncal cardiac defects, hypocalcemic hypoparathyroidism, T-cell mediated immune deficiency, and palate abnormalities. Less well recognized are learning, speech, feeding, and psychiatric disorders, and renal and musculoskeletal defects. Parathyroid and immune deficiencies in the same individual can progress or resolve with time. The 22q11.2 deletion can be inherited as an autosomal dominant or arise as a de novo deletion or translocation. Fluorescent in situ hybridization using cosmid probes mapping to the DiGeorge chromosomal region is a widely available method to detect the 22q11.2 deletion in metaphase chromosomes from cultured lymphocytes, amniocytes, or chorionic villi. The ubiquitin-fusion-degradation-1-like gene, expressed in embryonic branchial arches and in the conotruncus, appears to play a prominent role in the pathogenesis of the 22q11.2 deletion syndrome.

DiGeorge syndrome/chromosome 22q11.2 deletion syndrome

DiGeorge syndrome is characterized by conotruncal cardiac defects, hypocalcemia, and a hypoplastic thymus. Many, but not all, patients have a heterozygous deletion of chromosome 22q11.2. In its most severe form, it represents a devastating syndrome with high mortality. Patients with severe immunodeficiency are candidates for a thymic transplant or a fully matched bone marrow transplant. Fortunately, the majority of patients with either DiGeorge syndrome or chromosome 22q11.2 deletion syndrome have a mild to moderate immunodeficiency. These patients may develop recurrent infections or autoimmune disease.

Type I diabetes mellitus in a patient with chromosome 22q11.2 deletion syndrome

We describe a patient with type I diabetes, clinical findings consistent with velocardiofacial syndrome, and a chromosome 22q11.2 deletion. A nine-year-old boy presented with a history of polyuria, polydipsia, weight loss, hyperglycemia, ketosis, serum insulin antibodies, and a low C-peptide level. He had distinctive facial features, learning disabilities, short stature, and a history of glottic web and clubfoot. Although a normal karyotype was obtained, fluorescence in situ hybridization (FISH) revealed a submicroscopic deletion in the DiGeorge/velocardiofacial syndrome critical region at 22q11.2. His maternal half-brother also carried a chromosome 22q11.2 deletion. His mother has similar facial features and hypoparathyroidism. Autoimmune problems associated with chromosome 22q11.2 deletions have been reported. We suggest that the defects in immune regulation due to T-cell deficiency in chromosome 22q11.2 deletion syndrome may predispose to autoimmune disorders, including type I diabetes mellitus.

T cell receptor repertoire and function in patients with DiGeorge syndrome and velocardiofacial syndrome

DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS) are associated with chromosome 22q11.2 deletion. Limited information is available on the T cell receptor (TCR) Vbeta repertoire. We therefore investigated TCR Vbeta families in lymphocytes isolated from blood and thymic samples of seven patients with DGS and seven patients with VCFS, all with 22q11.2 deletion. We also studied activities related to TCR signalling including in vitro proliferation, anti-CD3-induced protein tyrosine phosphorylation, and susceptibility to apoptosis. Reduced CD3+ T cells were observed in most patients. Spontaneous improvement of T cell numbers was detected in patients, 3 years after the first study. Analysis of CD4+ and CD8+ TCR Vbeta repertoire in peripheral and thymic cells showed a normal distribution of populations even if occasional deletions were observed. Lymphoproliferative responses to mitogens were comparable to controls as well as anti-CD3-induced protein tyrosine phosphorylation. Increased anti-CD3-mediated apoptosis was observed in thymic cells. Our data support the idea that in patients surviving the correction of cardiac anomalies, the immune defect appears milder than originally thought, suggesting development of a normal repertoire of mature T cells.

Longitudinal analysis of lymphocyte function and numbers in the first year of life in chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion syndrome is a common syndrome typically consisting of variable cardiac defects, hypoparathyroidism, developmental delay, and immunodeficiency. The hemizygous deletion has variable effects on the immune system even within the same kindred, and the extent of the immunodeficiency is difficult to predict. Some patients have shown improvement over time; however, this is the first prospective longitudinal study of the dynamic nature of the immunodeficiency. Nineteen patients were studied prospectively between 1994 and 1997. The results of the newborn immunologic studies in the chromosome 22q11.2 deletion group were significantly different from those of a group of newborns with cardiac disease due to other causes. Peripheral blood T-cell numbers were decreased in the chromosome 22q11.2 deletion group, although T-cell function was largely preserved. The group as a whole demonstrated few changes in the first year of life, but a subset of patients with markedly diminished T-cell numbers did demonstrate improvement. Therefore, improvement in peripheral blood T-cell counts is variable in chromosome 22q11.2 deletion syndrome. The patients with the lowest T-cell counts improved the most in the first year of life.

Increased prevalence of immunoglobulin A deficiency in patients with the chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

We wished to determine the prevalence of immunoglobulin A (IgA) deficiency in patients with the chromosome 22q11.2 deletion syndrome. A total of 32 patients with the chromosome 22q11.2 deletion were examined for IgA deficiency. We report a 13% (n = 4) prevalence of IgA deficiency in patients with this syndrome. The odds ratio of IgA deficiency in this population is 14.20 (P < 0.0001). This confirms the occurrence of significant humoral deficits in this predominantly cellular immunodeficiency.

Lack of correlation between impaired T cell production, immunodeficiency, and other phenotypic features in chromosome 22q11.2 deletion syndromes

Monosomic deletions of chromosome 22q11.2 are the leading cause of DiGeorge syndrome, velocardiofacial syndrome, and conotruncal anomaly face syndrome. DiGeorge syndrome was originally described as an immunodeficiency disorder secondary to impaired T cell production due to thymic aplasia or hypoplasia; however, the frequency of immunodeficiency in the other clinical syndromes associated with the chromosome 22q11.2 microdeletion has not been previously investigated. This study examines the frequency and severity of impaired T cell production and immunodeficiency in chromosome 22q11.2 deletion syndromes and the relationship of the immunodeficiency to specific phenotypic features. Sixty patients over 6 months of age with the characteristic chromosome 22q11.2 deletion underwent immunologic evaluations. Seventy-seven percent of patients with chromosome 22q11.2 deletions were found to have evidence of immunocompromise. The severity of the immunodeficiency did not correlate with any particular phenotypic feature, nor was it restricted to patients who were categorized as having DiGeorge syndrome. Therefore, impaired T cell production and impaired immunologic function are common in patients with deletions of chromosome 22q11.2. The presence or severity of the immunocompromise cannot be predicted based on other phenotypic features and each child should be individually assessed for immune function.

Pulmonary diseases in children with severe combined immune deficiency and DiGeorge syndrome

Pulmonary disease is a common presenting feature and complication of T-cell immunodeficiency. We retrospectively reviewed 15 children with severe combined immune deficiency (SCID) and 19 children with DiGeorge syndrome at the time of their first presentation to the Royal Children's Hospital in the 15-year period from 1981 to 1995. In children with SCID, pulmonary disease was a common (67%) presenting feature and the organisms identified were Pneumocystis carinii (PCP) (n = 7), bacteria (n = 4), viruses (n = 3), and a fungus (n = 1). Late pulmonary complications included lower respiratory tract infections, bronchiolitis obliterans, and lymphointerstitial pneumonitis. Pulmonary infections were common (17 occasions) and the organisms identified were bacteria (n = 7), viruses (n = 6), fungi (n = 3), and Mycobacterium tuberculosis (n = 1). Pulmonary complications were responsible for 5 of 9 deaths. PCP was not identified as a late complication in any child, presumably as a result of effective prophylactic therapy. Although pulmonary disease was not a major presenting feature in children with DiGeorge syndrome, pulmonary complications were common. These included recurrent bacterial and viral infections and bronchomalacia, which complicated management and predisposed to morbidity and mortality, even in those without a T-cell defect. We conclude that pulmonary disease is a common manifestation in children with SCID and DiGeorge syndrome.