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

Chromosome 22q11.2 Deletion (DiGeorge Syndrome): Immunologic Features, Diagnosis, and Management

PURPOSE OF REVIEW

This review focuses on immunologic findings, relationships among immunologic findings and associated conditions of autoimmunity and atopy, and management of immunologic disease in chromosome 22q11.2 deletion syndrome (22q11.2DS, historically known as DiGeorge syndrome).

RECENT FINDINGS

The implementation of assessment of T cell receptor excision circles (TRECs) in newborn screening has led to increased detection of 22q11.2 deletion syndrome. While not yet applied in clinical practice, cell-free DNA screening for 22q11.2DS also has the potential to improve early detection, which may benefit prompt evaluation and management. Multiple studies have further elucidated phenotypic features and potential biomarkers associated with immunologic outcomes, including the development of autoimmune disease and atopy. The clinical presentation of 22q11.2DS is highly variable particularly with respect to immunologic manifestations. Time to recovery of immune system abnormalities is not well-defined in current literature. An understanding of the underlying causes of immunologic changes found in 22q11.2DS, and the progression and evolution of immunologic changes over the lifespan have expanded over time and with improved survival. An included case highlights the variability of presentation and potential severity of T cell lymphopenia in partial DiGeorge syndrome and demonstrates successful spontaneous immune reconstitution in partial DiGeorge syndrome despite initial severe T cell lymphopenia.

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.

Unusual occurrence of domestication syndrome amongst African mole-rats: Is the naked mole-rat a domestic animal?

The Naked mole-rat (NMR) is becoming a prominent model organism due to its peculiar traits, such as eusociality, extreme longevity, cancer resistance, and reduced pain sensitivity. It belongs to the African mole-rats (AMR), a family of subterranean rodents that includes solitary, cooperative breeding and eusocial species. We identified and quantified the domestication syndrome (DS) across AMR, a set of morphological and behavioural traits significantly more common and pronounced amongst domesticated animals than in their wild counterparts. Surprisingly, the NMR shows apparent DS traits when compared to the solitary AMR. Animals can self-domesticate when a reduction of the fear response is naturally selected, such as in islands with no predators, or to improve the group’s harmony in cooperative breeding species. The DS may be caused by alterations in the physiology of the neural crest cells (NCC), a transient population of cells that generate a full range of tissues during development. The NCC contribute to organs responsible for transmitting the fear response and various other tissues, including craniofacial bones. Therefore, mutations affecting the NCC can manifest as behavioural and morphological alterations in many structures across the body, as seen in neurocristopathies. We observed that all social AMRs are chisel-tooth diggers, an adaption to hard soils that requires the flattening of the skull. We hypothesise that chisel-tooth digging could impose a selective pressure on the NCC that triggered the DS’s appearance, possibly facilitating the evolution of sociality. Finally, we discuss how DS traits are neutral or beneficial for the subterranean niche, strategies to test this hypothesis and report well-studied mutations in the NMR that are associated with the NCC physiology or with the control of the fear response. In conclusion, we argue that many of the NMR’s unconventional traits are compatible with the DS and provide a hypothesis about its origins. Our model proposes a novel avenue to enhance the understanding of the extraordinary biology of the NMR.

Congenital Athymia: Genetic Etiologies, Clinical Manifestations, Diagnosis, and Treatment

Congenital athymia is an ultra-rare disease characterized by the absence of a functioning thymus. It is associated with several genetic and syndromic disorders including FOXN1 deficiency, 22q11.2 deletion, CHARGE Syndrome (Coloboma, Heart defects, Atresia of the nasal choanae, Retardation of growth and development, Genitourinary anomalies, and Ear anomalies), and Complete DiGeorge Syndrome. Congenital athymia can result from defects in genes that impact thymic organ development such as FOXN1 and PAX1 or from genes that are involved in development of the entire midline region, such as TBX1 within the 22q11.2 region, CHD7, and FOXI3. Patients with congenital athymia have profound immunodeficiency, increased susceptibility to infections, and frequently, autologous graft-versus-host disease (GVHD). Athymic patients often present with absent T cells but normal numbers of B cells and Natural Killer cells (T-B+NK+), similar to a phenotype of severe combined immunodeficiency (SCID); these patients may require additional steps to confirm the diagnosis if no known genetic cause of athymia is identified. However, distinguishing athymia from SCID is crucial, as treatments differ for these conditions. Cultured thymus tissue is being investigated as a treatment for congenital athymia. Here, we review what is known about the epidemiology, underlying etiologies, clinical manifestations, and treatments for congenital athymia.

Care of Children with DiGeorge Before and After Cultured Thymus Tissue Implantation

BACKGROUND

Children with complete DiGeorge anomaly (cDGA) have congenital athymia plus a myriad of other challenging clinical conditions. The term cDGA encompasses children with congenital athymia secondary to 22q11.2DS, CHARGE syndrome (coloboma, heart defects, choanal atresia, growth or mental retardation, genital abnormalities, and ear abnormalities and/or deafness), and other genetic abnormalities. Some children have no known genetic defects. Since 1993, more than 100 children with congenital athymia have been treated with cultured thymus tissue implantation (CTTI). Naïve T cells develop approximately 6 to 12 months after CTTI. Most of the children had significant comorbidities such as heart disease, hypoparathyroidism, and infections requiring complex clinical care post cultured thymus tissue implantation (CTTI).

OBJECTIVE

The purpose of this guidance is to assist multidisciplinary teams in caring for children with cDGA both before and after CTTI.

METHODS

Thirty-one specialists, in addition to the authors, were asked to share their experience in caring for children with cDGA at Duke University Health System, before and after CTTI. These specialists included physicians, nurses, dentists, therapists, and dieticians.

RESULTS

The goal of a multidisciplinary approach is to have children in the best possible condition for receiving CTTI and provide optimal care post CTTI through development of naïve T cells and beyond. The CTT (cultured thymus tissue) must be protected from high doses of steroids which can damage CTT. Organs must be protected from adverse effects of immunosuppression.

CONCLUSION

Creating a multidisciplinary team and a detailed plan of care for children with cDGA is important for optimal outcomes.

Inborn errors of thymic stromal cell development and function

As the primary site for T cell development, the thymus is responsible for the production and selection of a functional, yet self-tolerant T cell repertoire. This critically depends on thymic stromal cells, derived from the pharyngeal apparatus during embryogenesis. Thymic epithelial cells, mesenchymal and vascular elements together form the unique and highly specialised microenvironment required to support all aspects of thymopoiesis and T cell central tolerance induction. Although rare, inborn errors of thymic stromal cells constitute a clinically important group of conditions because their immunological consequences, which include autoimmune disease and T cell immunodeficiency, can be life-threatening if unrecognised and untreated. In this review, we describe the molecular and environmental aetiologies of the thymic stromal cell defects known to cause disease in humans, placing particular emphasis on those with a propensity to cause thymic hypoplasia or aplasia and consequently severe congenital immunodeficiency. We discuss the principles underpinning their diagnosis and management, including the use of novel tools to aid in their identification and strategies for curative treatment, principally transplantation of allogeneic thymus tissue.

Optimising immunisation in children with 22q11 microdeletion

BACKGROUND

The condition known as 22q11 microdeletion syndrome has a broad phenotypic spectrum, with many affected individuals experiencing mild-to-moderate immunodeficiency. Currently, there are significant variations in live vaccine practices and immunological testing prior to live vaccine administration due to safety concerns and limited established guidelines.

METHODS

Queensland Children's Hospital (QCH) Child Development Unit, offers a state-wide 22q11 microdeletion clinic. This is a retrospective single-centre review, capturing the majority of children with 22q11 microdeletion in Queensland, Australia. We describe the live vaccination status of 134 children, age 0 to 18 years under our care between 2000 and 2018, adverse events following immunisation (AEFI) and the proportion of children who received additional pneumococcal coverage. An immunological investigation pathway prior to live vaccine administration is proposed.

RESULTS

Of the 134 children, 124 were eligible for live vaccinations as per the Australian National Immunisation Program: 82% had received dose one of measles, mumps and rubella (MMR) vaccine, 77% had completed MMR dose two and 66% had completed varicella immunisation. There were no AEFI notifications reported. Of the total sample of children, 18% received a fourth dose of conjugate pneumococcal vaccine (Prevenar 7 or 13) and 16% received a dose of Pneumovax 23 from 4 years of age. Immunology workup practices were demonstrated to vary widely prior to live vaccine administration. Most patients' immune profiles were consistent with mild-to-moderate immunodeficiency.

CONCLUSION

We propose an immunological investigation and vaccination pathway with the aim of providing guidance and consistency to clinicians caring for children with 22q11 microdeletion.

Chromosome 22q11.2 deletion syndrome and DiGeorge syndrome

Chromosome 22q11.2 deletion syndrome is the most common microdeletion syndrome in humans. The effects are protean and highly variable, making a unified approach difficult. Nevertheless, commonalities have been identified and white papers with recommended evaluations and anticipatory guidance have been published. This review will cover the immune system in detail and discuss both the primary features and the secondary features related to thymic hypoplasia. A brief discussion of the other organ system involvement will be provided for context. The immune system, percolating throughout the body can impact the function of other organs through allergy or autoimmune disease affecting organs in deleterious manners. Our work has shown that the primary effect of thymic hypoplasia is to restrict T cell production. Subsequent homeostatic proliferation and perhaps other factors drive a Th2 polarization, most obvious in adulthood. This contributes to atopic risk in this population. Thymic hypoplasia also contributes to low regulatory T cells and this may be part of the overall increased risk of autoimmunity. Collectively, the effects are complex and often age-dependent. Future goals of improving thymic function or augmenting thymic volume may offer a direct intervention to ameliorate infections, atopy, and autoimmunity.

Phenotypical T Cell Differentiation Analysis: A Diagnostic and Predictive Tool in the Study of Primary Immunodeficiencies

Multiparametric flow cytometry (MFC) represents a rapid, highly reproducible, and sensitive diagnostic technology for primary immunodeficiencies (PIDs), which are characterized by a wide range of T cell perturbations and a broad clinical and genetic heterogeneity. MFC data from CD4+ and CD8+ T cell subsets were examined in 100 patients referred for Primary Immunodeficiencies to our center. Naïve, central memory, effector memory, and terminal effector memory cell differentiation stages were defined by the combined expression CD45RA/CD27 for CD4 and CD45RA/CCR7 for CD8. Principal component analysis (PCA), a non-hypothesis driven statistical analysis, was applied to analyze MFC data in order to distinguish the diverse PIDs. Among severe lymphopenic patients, those affected by severe combined and combined immunodeficiency (SCID and CID) segregated in a specific area, reflecting a homogenous, and a more severe T cell impairment, compared to other lymphopenic PID, such as thymectomized and partial DiGeorge syndrome patients. PID patients with predominantly antibody defects were distributed in a heterogeneous pattern, but unexpectedly PCA was able to cluster some patients' resembling CID, hence warning for additional and more extensive diagnostic tests and a diverse clinical management. In conclusion, PCA applied to T cell MFC data might help the physician to estimate the severity of specific PID and to diversify the clinical and diagnostic approach of the patients.

Clinical and immunological features in a cohort of patients with partial DiGeorge syndrome followed at a single center

DiGeorge syndrome (DGS) is a primary immunodeficiency characterized by various degrees of T-cell deficiency. In partial DGS (pDGS), other risk factors could predispose to recurrent infections, autoimmunity, and allergy. The aim of this study was to assess the effect of different factors in the development of infections, autoimmunity, and/or allergy in patients with pDGS. We studied 467 pDGS patients in follow-up at Great Ormond Street Hospital. Using a multivariate approach, we observed that palatal anomalies represent a risk factor for the development of recurrent otitis media with effusion. Gastroesophageal reflux/dysphagia and asthma/rhinitis represent a risk factor for the development of recurrent upper respiratory tract infections. Allergy and autoimmunity were associated with persistently low immunoglobulin M levels and lymphopenia, respectively. Patients with autoimmunity showed lower levels of CD3⁺, CD3⁺CD4⁺, and naïve CD4⁺CD45RA⁺CD27⁺ T lymphocytes compared with pDGS patients without autoimmunity. We also observed that the physiological age-related decline of the T-cell number was slower in pDGS patients compared with age-matched controls. The age-related recovery of the T-cell number depended on a homeostatic peripheral proliferation of T cells, as suggested by an accelerated decline of the naïve T lymphocytes in pDGS as well as a more skewed T-cell repertoire in older pDGS patients. These evidences suggest that premature CD4⁺ T-cell aging and lymphopenia induced spontaneous peripheral T-cell proliferation might contribute to the pathogenesis of autoimmunity in patients with pDGS. Infections in these patients represent, in most of the cases, a complication of anatomical or gastroenterological anomalies rather than a feature of the underlying immunodeficiency.

Microdeletion 22q11.2 syndrome: Does thymus incidental surgical resection affect its immunological profile?

BACKGROUND

The del22q11 syndrome patients present immunological abnormalities associated to thymus alterations. Up to 75% of them present cardiopathies and thymus is frequently removed during surgery. The thymectomy per se has a deleterious effect concerning lymphocyte subpopulations, and T cell function. When compared to healthy controls, these patients have higher infections propensity of variable severity. The factors behind these variations are unknown. We compared immunological profiles of del22q11.2 Syndrome patients with and without thymectomy to establish its effect in the immune profile.

METHODS

Forty-six del22q11.2 syndrome patients from 1 to 16 years old, 19 of them with partial or total thymectomy were included. Heart disease type, heart surgery, infections events and thymus resection were identified. Immunoglobulin levels, flow cytometry for lymphocytes subpopulations and TREC levels were determined, and statistical analyses were performed.

RESULTS

The thymectomy group had a lower lymphocyte index, both regarding total cell count and when comparing age-adjusted Z scores. Also, CD3+, CD4+ and CD8+ lower levels were observed in this group, the lowest count in those patients who had undergone thymus resection during the first year of life. Their TREC level median was 23.6/μL vs 16.1μL in the non-thymus group (p=0.22). No differences were identified regarding immunoglobulin levels or infection events frequencies over the previous year.

CONCLUSION

Patients with del22q11.2 syndrome subjected to thymus resection present lower lymphocyte and TREC indexes when compared to patients without thymectomy. This situation may be influenced by the age at the surgery and the time elapsed since the procedure.

Variable immune deficiency related to deletion size in chromosome 22q11.2 deletion syndrome

The clinical features of 22q11.2 deletion syndrome include virtually every organ of the body. This review will focus on the immune system and the differences related to deletion breakpoints. A hypoplastic thymus was one of the first features described in this syndrome and low T cell counts, as a consequence of thymic hypoplasia, are the most commonly described immunologic feature. These are most prominently seen in early childhood and can be associated with increased persistence of viruses. Later in life, evidence of T cell exhaustion may be seen and secondary deficiencies of antibody function have been described. The relationship of the immunodeficiency to the deletion breakpoints has been understudied due to the infrequent analysis of people carrying smaller deletions. This manuscript will review the immune deficiency in 22q11.2 deletion syndrome and describe differences in the T cell counts related to the deletion breakpoints. Distal, non-TBX1 inclusive deletions, were found to be associated with better T cell counts. Another new finding is the relative preservation of T cell counts in those patients with a 22q11.2 duplication.

The immune deficiency of chromosome 22q11.2 deletion syndrome

The syndrome originally described by Dr. Angelo DiGeorge had immunodeficiency as a central component. When a 22q11.2 deletion was identified as the cause in the majority of patients with DiGeorge syndrome, the clinical features of 22q11.2 deletion syndrome became so expansive that the immunodeficiency became less prominent in our thinking about the syndrome. This review will focus on the immune system and the changes in our understanding over the past 50 years. Initially characterized as a pure defect in T cell development, we now appreciate that many of the clinical features related to the immunodeficiency are well downstream of the limitation imposed by a small thymus. Dysfunctional B cells presumed to be secondary to compromised T cell help, issues related to T cell exhaustion, and high rates of atopy and autoimmunity are aspects of management that require consideration for optimal clinical care and for designing a cogent monitoring approach. New data on atopy are presented to further demonstrate the association.

Primary immunodeficiencies associated with EBV-Induced lymphoproliferative disorders

Primary immunodeficiency diseases (PIDs) are a subgroup of inherited immunological disorders that increase susceptibility to viral infections. Among the range of viral pathogens involved, EBV remains a major threat because of its high prevalence of infection among the adult population and its tendency to progress to life-threatening lymphoproliferative disorders (LPDs) and/or malignancy. The high mortality in immunodeficient patients with EBV-driven LPDs, despite institution of diverse and often intensive treatments, prompts the need to better study these PIDs to identify and understand the affected molecular pathways that increase susceptibility to EBV infection and progression. In this article, we have provided a detailed literature review of the reported cases of EBV-driven LPDs in patients with PID. We discuss the PIDs associated with development of EBV-LPDs. Then, we review the nature and the therapeutic outcome of common EBV- driven LPDs in the PID patients and review the mechanisms common to the major PIDs. Deep study of these common pathways and gaining a better insight into the disease nature and outcomes, may lead to earlier diagnosis of the disease, choosing the best treatment modalities available and development of novel therapeutic strategies to decrease morbidity and mortality brought about by EBV infection.

Application of Flow Cytometry in the Evaluation of Primary Immunodeficiencies

Primary immunodeficiency disorders (PIDDs) are a heterogeneous group of inherited disorders of the immune system. Currently more than 250 different PIDDs with a known genetic defect have been recognized. The diagnosis of many of these disorders is supported strongly by a wide variety of flow cytometry applications. Flow cytometry offers a rapid and sensitive tool for diagnosis and classification of PIDDs. It is applicable in the initial workup and subsequent management of several primary immunodeficiency diseases. As our understanding of the pathogenesis and management of these diseases increases, the majority of these tests can be easily established in the diagnostic laboratory. Thus, the focus of this article is on the application of flow cytometry in the diagnosis and/or evaluation of PIDDs.

22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11.2DS) is the most common chromosomal microdeletion disorder, estimated to result mainly from de novo non-homologous meiotic recombination events occurring in approximately 1 in every 1,000 fetuses. The first description in the English language of the constellation of findings now known to be due to this chromosomal difference was made in the 1960s in children with DiGeorge syndrome, who presented with the clinical triad of immunodeficiency, hypoparathyroidism and congenital heart disease. The syndrome is now known to have a heterogeneous presentation that includes multiple additional congenital anomalies and later-onset conditions, such as palatal, gastrointestinal and renal abnormalities, autoimmune disease, variable cognitive delays, behavioural phenotypes and psychiatric illness - all far extending the original description of DiGeorge syndrome. Management requires a multidisciplinary approach involving paediatrics, general medicine, surgery, psychiatry, psychology, interventional therapies (physical, occupational, speech, language and behavioural) and genetic counselling. Although common, lack of recognition of the condition and/or lack of familiarity with genetic testing methods, together with the wide variability of clinical presentation, delays diagnosis. Early diagnosis, preferably prenatally or neonatally, could improve outcomes, thus stressing the importance of universal screening. Equally important, 22q11.2DS has become a model for understanding rare and frequent congenital anomalies, medical conditions, psychiatric and developmental disorders, and may provide a platform to better understand these disorders while affording opportunities for translational strategies across the lifespan for both patients with 22q11.2DS and those with these associated features in the general population.

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.

ICON: the early diagnosis of congenital immunodeficiencies

Primary immunodeficiencies are intrinsic defects in the immune system that result in a predisposition to infection and are frequently accompanied by a propensity to autoimmunity and/or immunedysregulation. Primary immunodeficiencies can be divided into innate immunodeficiencies, phagocytic deficiencies, complement deficiencies, disorders of T cells and B cells (combined immunodeficiencies), antibody deficiencies and immunodeficiencies associated with syndromes. Diseases of immune dysregulation and autoinflammatory disorder are many times also included although the immunodeficiency in these disorders are often secondary to the autoimmunity or immune dysregulation and/or secondary immunosuppression used to control these disorders. Congenital primary immunodeficiencies typically manifest early in life although delayed onset are increasingly recognized. The early diagnosis of congenital immunodeficiencies is essential for optimal management and improved outcomes. In this International Consensus (ICON) document, we provide the salient features of the most common congenital immunodeficiencies.

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 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.

DiGeorge Syndrome Presenting as Hypocalcaemia-Induced Seizures in Adulthood

Introduction. DiGeorge syndrome is a developmental defect commonly caused by a microdeletion on the long arm of chromosome 22 or less frequently by a deletion of the short arm of chromosome 10. Case report. We report a case of a gentleman with mild dysmorphic features who presented with hypocalcaemia-induced seizures and an associated thyroid mass with a background of learning difficulties and abnormal immune function. Discussion. DiGeorge syndrome was initially described in 1967 by Angelo DiGeorge. The majority of cases are due to a novel mutation. The resulting learning difficulties, congenital heart disease, palatal abnormalities, hypoplasia/aplasia of the parathyroid and thymus glands, and immune deficiency generally lead to diagnosis in childhood. Presentation in adulthood is rare but must be borne in mind when dealing with cases of hypocalcaemia even in the absence of florid phenotypic features. A link with malignant disease has also been reported and should lead to prompt investigation of concerning masses.

A Case of CATCH22 Syndrome Diagnosed in Postmenopausal Woman

CATCH 22 Syndrome is caused by chromosome 22q11.2 microdeletion, characterized by developmental abnormalities of the third and fourth pharyngeal pouches. It has a prevalence estimated at 1:3,000-1:9,000. Most deletions occurs sporadic, but autosomal dominant inheritance observed in 6-10% of cases. CATCH22 often diagnosed due to hypocalcemia during neonatal period or decreased immunity or facial defect, so it is very rare being diagnosed CATCH22 in adulthood. We report a 57 year old female who referred to mental change due to hypocalcemia and is diagnosed CATCH22. She was presented with hypoparathyroidism, single kidney due to renal agenesis, and mild facial defect. Our patient responded well to calcium and vitamin D treatment and she is on follow-up in outpatient clinic.

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.

Immune evaluation and vaccine responses in Down syndrome: evidence of immunodeficiency?

BACKGROUND

Patients with Down syndrome (DS) appear to be at a greater risk for serious infections, but it is unclear whether this is due to anatomic variations or intrinsic immune defects.

OBJECTIVE

We assessed a cohort of pediatric subjects with DS to determine if immunological abnormalities indeed account for the excess infections.

METHODS

We performed quantitative assessment of T-independent (type 2 - pneumococcal polysaccharide vaccine) and T-dependent Ab responses (with inactivated seasonal influenza vaccine) along with numerical quantitation of lymphocyte subpopulations and thymic output in a random population sample of children with DS (cases) along with family-matched sibling or community controls.

RESULTS

Median serum IgG levels were significantly higher in cases (1090 mg/dL) as compared with controls (808 mg/dL, P=0.02). Cases had significantly lower median CD4 T cell counts than the controls (636 cells/μL, P=0.01). Cases had reduced CD19 B cell counts and CD19% than the controls (P=0.009 and 0.006 respectively). Cases also showed decreased total memory (CD19+CD27+, P=0.002) and class-switched memory (CD19+CD27+IgM-IgD-, P=0.004) B cells. The median CD4 recent thymic emigrant (RTE) in females and males cases was lower than controls (P=0.007 and 0.07 respectively). Cases had a lower median T cell receptor excision circle (TREC) count of 2556 as compared to the controls count of 5216, P<0.006 although both the cases and controls were within the established reference range. There were no differences in the percentage of cases and controls who responded to inactivated influenza vaccine, but the response to polysaccharide pneumococcal vaccine was suboptimal in cases.

CONCLUSIONS

Our study suggests that there are subtle abnormalities in both humoral and cellular arms of the immune response in children with DS as compared to the control subjects.

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.

Understanding the genetic regulation of IgE production

Immunoglobulin E (IgE) is a key mediator of anti-parasitic and anti-tumour immunity. However it is also a critical component of atopic and autoimmune diseases, and elevated serum IgE levels are a common indicator of immune dysregulation. In this review we survey the literature on genetic associations of elevated IgE in humans and mice. We find that defects in a limited number of pathways explain the majority of gene associations with IgE. Commonly, elevated IgE is associated with defects in Th bias and B cell class switching, severe T cell tolerance defects and defects in immunity at the host-environment interface. These genetic data demonstrate the mechanisms of control over IgE production and the manner in which they can be circumvented.

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.

Both normal memory counts and decreased naive cells favor intrinsic defect over early senescence of Down syndrome T lymphocytes

Because of their increased malignancies, autoimmune diseases, and infections, patients with Down syndrome (DS) show features of immunodeficiency. The DS thymus and T lymphocyte subsets have indeed proven to be different, and this has been interpreted as precocious aging. Our study on T lymphocyte subpopulations in DS shows that the normal expansion of naive helper (CD4CD45RA) and cytotoxic (CD8CD45RACD27) T lymphocytes is lacking in the first years of life; this is more logically explainable with an intrinsic T lymphocyte defect. Furthermore, memory cell numbers are not different from age-matched controls (AMC), which does not support the hypothesis of precocious aging. Although the absolute numbers of T lymphocyte subpopulations approach AMC levels toward adulthood, the persistent clinical problems suggest that these cells may not function optimally. However, the clinical picture does not fit severe T lymphocyte deficiency. The latter concept is also supported by our finding that cytomegalovirus (CMV)-seropositive DS children show similar numbers of terminally differentiated cytotoxic T lymphocytes when compared with healthy children, not increased numbers as are seen in immunocompromised hosts.

Thymus transplantation

Thymus transplantation is a promising investigational therapy for infants born with no thymus. Because of the athymia, these infants lack T cell development and have a severe primary immunodeficiency. Although thymic hypoplasia or aplasia is characteristic of DiGeorge anomaly, in "complete" DiGeorge anomaly, there is no detectable thymus as determined by the absence of naive (CD45RA(+), CD62L(+)) T cells. Transplantation of postnatal allogeneic cultured thymus tissue was performed in sixty subjects with complete DiGeorge anomaly who were under the age of 2 years. Recipient survival was over 70%. Naive T cells developed 3-5 months after transplantation. The graft recipients were able to discontinue antibiotic prophylaxis, and immunoglobulin replacement. Immunosuppression was used in a subset of subjects but was discontinued when naive T cells developed. The adverse events have been acceptable with thyroid disease being the most common. Research continues on mechanisms underlying immune reconstitution after thymus transplantation.

DiGeorge Syndrome: a not so rare disease

INTRODUCTION

The DiGeorge Syndrome was first described in 1968 as a primary immunodeficiency resulting from the abnormal development of the third and fourth pharyngeal pouches during embryonic life. It is characterized by hypocalcemia due to hypoparathyroidism, heart defects, and thymic hypoplasia or aplasia. Its incidence is 1:3000 live births and, despite its high frequency, little is known about its natural history and progression. ←This is probably due to diagnostic difficulties and the great variety of names used to describe it, such as velocardiofacial, Shprintzen, DiGeorge, and CATCH 22 Syndromes, as well as conotruncal facial anomaly. All represent the same genetic condition, chromosome 22q11.2 deletion, which might have several clinical expressions.

OBJECTIVES

To describe clinical and laboratorial data and phenotypic characteristics of patients with DiGeorge Syndrome.

METHODS

Patients underwent standard clinical and epidemiological protocol and tests to detect heart diseases, facial abnormalities, dimorphisms, neurological or behavioral disorders, recurrent infections and other comorbidities.

RESULTS

Of 14 patients (8m - 18y11m), only one did not have 22q11.2 deletion detected. The main findings were: conotruncal malformation (n = 12), facial abnormalities (n = 11), hypocalcemia (n = 5) and low lymphocyte count (n=2).

CONCLUSION

The authors pointed out the necessity of DGS suspicion in all patient presenting with heart defects, facial abnormalities (associated or not with hypocalcemia), and immunological disorders because although frequency of DGS is high, few patients with a confirmed diagnosis are followed up.

CHARGE (coloboma, heart defect, atresia choanae, retarded growth and development, genital hypoplasia, ear anomalies/deafness) syndrome and chromosome 22q11.2 deletion syndrome: a comparison of immunologic and nonimmunologic phenotypic features

OBJECTIVES

CHARGE (coloboma, heart defect, atresia choanae, retarded growth and development, genital hypoplasia, ear anomalies/deafness) syndrome and chromosome 22q11.2 deletion syndrome are known to have significant clinical overlap including cardiac anomalies, ear abnormalities, hearing loss, developmental delay, renal abnormalities, and cleft palate. Immunodeficiency has been well documented in 22q11.2 deletion, but there has been limited recognition of this potentially serious complication in CHARGE syndrome. The goals of our study were to identify clinical features unique to CHARGE syndrome or 22q11.2 deletion and to describe the spectrum of immunodeficiency found in patients with CHARGE syndrome.

METHODS

This study included 25 children diagnosed with CHARGE syndrome with positive CHD7 mutations through the Children's Hospital of Philadelphia genetics program. Clinical features and laboratory findings were reviewed retrospectively. We compared our findings to data available for a large cohort of patients with 22q11.2 deletion syndrome followed in our clinical genetics program.

RESULTS

Features found more commonly in CHARGE syndrome included coloboma, choanal atresia, facial nerve palsy, tracheoesophageal fistula, and genital hypoplasia in boys. A high incidence of marked hypocalcemia was observed in our study group (72%). We found a spectrum of cell-mediated immunodeficiency in our study group, which ranged from lymphopenia (60%) to severe combined immunodeficiency (8%). Defects in humoral immunity were documented in 4 patients and included severe hypogammaglobulinemia with decreased T-cell numbers, transient hypogammaglobulinemia during infancy, and immunoglobulin A deficiency.

CONCLUSIONS

The presence of coloboma, choanal atresia, facial nerve palsy, tracheoesophageal fistula, or genital hypoplasia in boys should alert the clinician to the possibility of CHARGE syndrome rather than the 22q11.2 deletion. Molecular testing for CHD7 mutations may help to confirm the diagnosis. In this study, significant hypocalcemia and lymphopenia occurred more frequently in patients with CHARGE syndrome than in those with 22q11.2 deletion syndrome. Early inclusion of immunologists to the multidisciplinary care team (as with 22q11.2 deletion) may be of great benefit to affected patients.

Intrinsic defect of the immune system in children with Down syndrome: a review

Down syndrome (DS) is the most frequent cause of mental retardation in man. Immunological changes in DS have been observed since the 1970s. The neurological system appears to be ageing precociously, with early occurrence of Alzheimer disease; until now, the observed immunological differences have been interpreted in the same context. Looking back at past and present results of immunological studies in DS children in relation to the clinical consequences they suffer, we conclude that it is more likely that the DS immune system is intrinsically deficient from the very beginning.

Persistent low thymic activity and non-cardiac mortality in children with chromosome 22q11.2 microdeletion and partial DiGeorge syndrome

A subgroup of patients with 22q11.2 microdeletion and partial DiGeorge syndrome (pDGS) appears to be susceptible to non-cardiac mortality (NCM) despite sufficient overall CD4(+) T cells. To detect these patients, 20 newborns with 22q11.2 microdeletion and congenital heart disease were followed prospectively for 6 years. Besides detailed clinical assessment, longitudinal monitoring of naive CD4(+) and cytotoxic CD3(+)CD8(+) T cells (CTL) was performed. To monitor thymic activity, we analysed naive platelet endothelial cell adhesion molecule-1 (CD31(+)) expressing CD45RA(+)RO(-)CD4(+) cells containing high numbers of T cell receptor excision circle (T(REC))-bearing lymphocytes and compared them with normal values of healthy children (n = 75). Comparing two age periods, low overall CD4(+) and naive CD4(+) T cell numbers were observed in 65%/75%, respectively, of patients in period A (< 1 year) declining to 22%/50%, respectively, of patients in period B (> 1/< 7 years). The percentage of patients with low CTLs (< P10) remained robust until school age (period A: 60%; period B: 50%). Low numbers of CTLs were associated with abnormally low naive CD45RA(+)RO(-)CD4(+) T cells. A high-risk (HR) group (n = 11) and a standard-risk (SR) (n = 9) group were identified. HR patients were characterized by low numbers of both naive CD4(+) and CTLs and were prone to lethal infectious and lymphoproliferative complications (NCM: four of 11; cardiac mortality: one of 11) while SR patients were not (NCM: none of nine; cardiac mortality: two of nine). Naive CD31(+)CD45RA(+)RO(-)CD4(+), naive CD45RA(+)RO(-)CD4(+) T cells as well as T(RECs)/10(6) mononuclear cells were abnormally low in HR and normal in SR patients. Longitudinal monitoring of naive CD4(+) and cytotoxic T cells may help to discriminate pDGS patients at increased risk for NCM.

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.

Unravelling the association of partial T-cell immunodeficiency and immune dysregulation

Partial T-cell immunodeficiencies constitute a heterogeneous cluster of disorders characterized by an incomplete reduction in T-cell number or activity. The immune deficiency component of these diseases is less severe than that of the severe T-cell immunodeficiencies and therefore some ability to respond to infectious organisms is retained. Unlike severe T-cell immunodeficiencies, however, partial immunodeficiencies are commonly associated with hyper-immune dysregulation, including autoimmunity, inflammatory diseases and elevated IgE production. This causative association is counter-intuitive--immune deficiencies are caused by loss-of-function changes to the T-cell component, whereas the coincident autoimmune symptoms are the consequence of gain-of-function changes. This Review details the genetic basis of partial T -cell immunodeficiencies and draws on recent advances in mouse models to propose mechanisms by which a reduction in T-cell numbers or function may disturb the population-dependent balance between activation and tolerance.

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.

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.