Identification of 22q11.2 Deletion Syndrome via Newborn Screening for Severe Combined Immunodeficiency

Utilization of next-generation sequencing to define the role of heterozygous FOXN1 variants in immunodeficiency

Background

Forkhead box protein N1 (FOXN1) transcription factor plays an essential role in the development of thymic epithelial cells, required for T-cell differentiation, maturation, and function. Biallelic pathogenic variants in FOXN1 cause severe combined immunodeficiency (SCID). More recently, heterozygous variants in FOXN1, identified by restricted gene panels, were also implicated with causing a less severe and variable immunodeficiency.

Objective

We undertook longitudinal follow-up and advanced genetic investigations, including whole exome sequencing and whole genome sequencing, of newborns with a heterozygous variant in FOXN1.

Methods

Five patients (3 female, 2 male) have been followed since they were first detected with low T-cell receptor excision circles during newborn screening for SCID. Patients underwent immune evaluation as well as genetic testing, including a primary immunodeficiency panel, whole exome sequencing, and whole genome sequencing in some cases.

Results

Median follow-up time was 6.5 years. Initial investigations revealed low CD3+ T lymphocytes in all patients. One patient presented with extremely low lymphocyte counts and depressed phytohemagglutinin responses leading to a tentative diagnosis of SCID. Over a period of 2 years, CD3+ T-cell counts rose, although in some patients it remained borderline low. One of 5 children continues to experience recurrent upper respiratory infections and asthma episodes. The remaining are asymptomatic except for eczema in 2 of 5 cases. Lymphocyte proliferation responses to phytohemagglutinin were initially low in 3 patients but normalized by age 10 months. In 3 of 5 cases, T lymphocyte counts remain low/borderline low.

Conclusion

In cases of monoallelic FOXN1 variants, using whole exome sequencing and whole genome sequencing to rule out possible other significant pathogenic variants allowed us to proceed with confidence in a conservative manner, even in extreme cases consistent with newborn screen-positive early presentation of SCID.

Understanding the Variability of 22q11.2 Deletion Syndrome: The Role of Epigenetic Factors

Initially described as a triad of immunodeficiency, congenital heart defects and hypoparathyroidism, 22q11.2 deletion syndrome (22q11.2DS) now encompasses a great amount of abnormalities involving different systems. Approximately 85% of patients share a 3 Mb 22q11.2 region of hemizygous deletion in which 46 protein-coding genes are included. However, the hemizygosity of the genes of this region cannot fully explain the clinical phenotype and the phenotypic variability observed among patients. Additional mutations in genes located outside the deleted region, leading to "dual diagnosis", have been described in 1% of patients. In some cases, the hemizygosity of the 22q11.2 region unmasks autosomal recessive conditions due to additional mutations on the non-deleted allele. Some of the deleted genes play a crucial role in gene expression regulation pathways, involving the whole genome. Typical miRNA expression patterns have been identified in 22q11.2DS, due to an alteration in miRNA biogenesis, affecting the expression of several target genes. Also, a methylation epi-signature in CpG islands differentiating patients from controls has been defined. Herein, we summarize the evidence on the genetic and epigenetic mechanisms implicated in the pathogenesis of the clinical manifestations of 22q11.2 DS. The review of the literature confirms the hypothesis that the 22q11.2DS phenotype results from a network of interactions between deleted protein-coding genes and altered epigenetic regulation.

The Subtlety of 22q11.2 Deletion Syndrome in a Preterm Neonate

To date, 22q11.2 deletion syndrome (DS) is regarded as the most commonly diagnosed DS in humans. The location of the deletion on chromosome 22 affects the phenotypic presentation, which ranges from subtle to severe. Common manifestations include congenital heart defects, calcium deficiency, clefts and other midline defects, immunodeficiencies, and neurocognitive delay. This wide range of clinical manifestations can complicate diagnostic reasoning as many align with other disease processes commonly observed in preterm neonates. This article presents the case of a preterm neonate born at 25-weeks' gestation with 22q11.2 DS. The clinical presentation of this neonate included a right aortic arch, ventricular septal defect, hypocalcemia, borderline severe combined immunodeficiency, and abnormal thyroid function. The infant's hospital course is followed to highlight the challenges clinicians face when suspicious of a genetic disorder in a preterm neonate.

Chromosome 22q11.2 Deletion Syndrome: A Comprehensive Review of Molecular Genetics in the Context of Multidisciplinary Clinical Approach

The 22q11.2 deletion syndrome is a multisystemic disorder characterized by a marked variability of phenotypic features, making the diagnosis challenging for clinicians. The wide spectrum of clinical manifestations includes congenital heart defects-most frequently conotruncal cardiac anomalies-thymic hypoplasia and predominating cellular immune deficiency, laryngeal developmental defects, midline anomalies with cleft palate and velar insufficiency, structural airway defects, facial dysmorphism, parathyroid and thyroid gland hormonal dysfunctions, speech delay, developmental delay, and neurocognitive and psychiatric disorders. Significant progress has been made in understanding the complex molecular genetic etiology of 22q11.2 deletion syndrome underpinning the heterogeneity of clinical manifestations. The deletion is caused by chromosomal rearrangements in meiosis and is mediated by non-allelic homologous recombination events between low copy repeats or segmental duplications in the 22q11.2 region. A range of genetic modifiers and environmental factors, as well as the impact of hemizygosity on the remaining allele, contribute to the intricate genotype-phenotype relationships. This comprehensive review has been aimed at highlighting the molecular genetic background of 22q11.2 deletion syndrome in correlation with a clinical multidisciplinary approach.

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.

Human thymus in health and disease: Recent advances in diagnosis and biology

The thymus is the crucial tissue where thymocytes develop from hematopoietic precursors that originate from the bone marrow and differentiate to generate a repertoire of mature T cells able to respond to foreign antigens while remaining tolerant to self-antigens. Until recently, most of the knowledge on thymus biology and its cellular and molecular complexity have been obtained through studies in animal models, because of the difficulty to gain access to thymic tissue in humans and the lack of in vitro models able to faithfully recapitulate the thymic microenvironment. This review focuses on recent advances in the understanding of human thymus biology in health and disease obtained through the use of innovative experimental techniques (eg. single cell RNA sequencing, scRNAseq), diagnostic tools (eg. next generation sequencing), and in vitro models of T-cell differentiation (artificial thymic organoids) and thymus development (eg. thymic epithelial cell differentiation from embryonic stem cells or induced pluripotent stem cells).

Updated clinical practice recommendations for managing children with 22q11.2 deletion syndrome

This review aimed to update the clinical practice guidelines for managing children and adolescents with 22q11.2 deletion syndrome (22q11.2DS). The 22q11.2 Society, the international scientific organization studying chromosome 22q11.2 differences and related conditions, recruited expert clinicians worldwide to revise the original 2011 pediatric clinical practice guidelines in a stepwise process: (1) a systematic literature search (1992-2021), (2) study selection and data extraction by clinical experts from 9 different countries, covering 24 subspecialties, and (3) creation of a draft consensus document based on the literature and expert opinion, which was further shaped by survey results from family support organizations regarding perceived needs. Of 2441 22q11.2DS-relevant publications initially identified, 2344 received full-text reviews, including 1545 meeting criteria for potential relevance to clinical care of children and adolescents. Informed by the available literature, recommendations were formulated. Given evidence base limitations, multidisciplinary recommendations represent consensus statements of good practice for this evolving field. These recommendations provide contemporary guidance for evaluation, surveillance, and management of the many 22q11.2DS-associated physical, cognitive, behavioral, and psychiatric morbidities while addressing important genetic counseling and psychosocial issues.

Influence of Parent-of-Origin on Intellectual Outcomes in the Chromosome 22q11.2 Deletion Syndrome

Learning and intellectual disabilities are hallmark features of 22q11.2 deletion syndrome. Data are limited, however, regarding influences on full-scale IQ (FSIQ). Here, we investigated possible 22q11.2 deletion parent-of-origin effects. In 535 individuals, we compared FSIQ (≥50), 481 with de novo and 54 with inherited 22q11.2 deletions. In the subsets with data available, we examined parent-of-origin effects on FSIQ. We used linear regression models to account for covariates. Median FSIQ was significantly higher in de novo vs. inherited deletions (77; range 50−116 vs. 67; range 50−96, p < 0.0001). Results remained significant using a regression model accounting for age at IQ testing, sex and cohort site. No significant parent-of-origin differences in FSIQ were observed for de novo deletions (n = 81, 63.0% maternal; p = 0.6882). However, median FSIQ was significantly lower in maternally than in paternally inherited familial deletions (65, range 50−86 vs. 71.5, range 58−96, respectively, p = 0.0350), with the regression model indicating an ~8 point decrement in FSIQ for this variable (p = 0.0061). FSIQ is higher on average in de novo than in inherited 22q11.2 deletions, regardless of parental origin. However, parent-of-origin appears relevant in inherited deletions. The results have potential clinical implications with further research needed to delineate possible actionable mechanisms.

Long-Term Follow-Up of Newborns with 22q11 Deletion Syndrome and Low TRECs

Background

Population-based neonatal screening using T-cell receptor excision circles (TRECs) identifies infants with profound T lymphopenia, as seen in cases of severe combined immunodeficiency, and in a subgroup of infants with 22q11 deletion syndrome (22q11DS).

Purpose

To investigate the long-term prognostic value of low levels of TRECs in newborns with 22q11DS.

Methods

Subjects with 22q11DS and low TRECs at birth (22q11Low, N=10), matched subjects with 22q11DS and normal TRECs (22q11Normal, N=10), and matched healthy controls (HC, N=10) were identified. At follow-up (median age 16 years), clinical and immunological characterizations, covering lymphocyte subsets, immunoglobulins, TRECs, T-cell receptor repertoires, and relative telomere length (RTL) measurements were performed.

Results

At follow-up, the 22q11Low group had lower numbers of naïve T-helper cells, naïve T-regulatory cells, naïve cytotoxic T cells, and persistently lower TRECs compared to healthy controls. Receptor repertoires showed skewed V-gene usage for naïve T-helper cells, whereas for naïve cytotoxic T cells, shorter RTL and a trend towards higher clonality were found. Multivariate discriminant analysis revealed a clear distinction between the three groups and a skewing towards Th17 differentiation of T-helper cells, particularly in the 22q11Low individuals. Perturbations of B-cell subsets were found in both the 22q11Low and 22q11Normal group compared to the HC group, with larger proportions of naïve B cells and lower levels of memory B cells, including switched memory B cells.

Conclusions

This long-term follow-up study shows that 22q11Low individuals have persistent immunologic aberrations and increased risk for immune dysregulation, indicating the necessity of lifelong monitoring.

Clinical Implications

This study elucidates the natural history of childhood immune function in newborns with 22q11DS and low TRECs, which may facilitate the development of programs for long-term monitoring and therapeutic choices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01201-5.

Clinical Features in a Large Cohort of Patients With 22q11.2 Deletion Syndrome

OBJECTIVES

To evaluate various clinical aspects, specifically regarding immune status, in a large cohort of patients with DiGeorge syndrome.

STUDY DESIGN

Data were collected for 98 patients with DiGeorge syndrome treated at a tertiary medical center. This included general information, laboratory results, and clinical features.

RESULTS

The median age at diagnosis was 2.0 years (range, 0.0-36.5 years). The most common symptoms that led to diagnosis were congenital heart defect, speech delay, palate anomalies, and developmental delay. Common clinical features included recurrent infections (76 patients), congenital heart diseases (61 patients), and otorhinolaryngology disorders (61 patients). Twenty patients had anemia; the incidence was relatively high among patients aged 6-59 months. Thrombocytopenia was present in 20 patients. Recurrent chest infections were significantly higher in patients with T cell and T cell subset deficiencies. Decreased T cell receptor excision circles were more common with increasing age (P < .001). Of the 27 patients hospitalized due to infection, pneumonia was a leading cause in 13.

CONCLUSIONS

Awareness of DiGeorge syndrome's typical and uncommon characteristics is important to improve diagnosis, treatment, surveillance, and follow-up.

Reasons of the delayed vaccination, recommendations and safety of vaccination in children with congenital heart disease in Zhejiang, China

There has been a considerable controversy about vaccination practices in Children with congenital heart disease (CHD) in China. This study aims to identify the reasons for deferring vaccination among the patient population attending the Vaccination Consultation Clinic in Zhejiang Province and the safety of their vaccination. We analyzed the data of 2442 children with CHD, who visited to our clinic from January 2016 to March 2019. A questionnaire survey was conducted to investigate the reasons for their delayed vaccination. Information about the following vaccination and Adverse Events Following Immunization (AEFI) was collected. Most of the enrolled children did not receive vaccines on time before consultation. The reasons for their deferring vaccination included: 1. Providers in the community health center refused to administer vaccines (77.6%); 2. Parents' concerns about the safety of vaccines (19.0%); 3. Parents' doubts about the efficiency of vaccines after certain drug applications (3.4%). According to the evaluation reports issued by the Vaccination Consultation Clinic, 83.7% of CHD children were recommended to be vaccinated on the nationally recommended schedule, 14.4% were recommended to defer some specific vaccination, and 1.9% were recommended to defer all vaccination. Among the group who received vaccines on nationally recommended schedule, the AEFI rate was 33.5/100 000. No rare or serious rare vaccine reactions were observed. Our study provides evidence that routine vaccination is safe in the majority of this patient population.

Estimate of the contemporary live-birth prevalence of recurrent 22q11.2 deletions: a cross-sectional analysis from population-based newborn screening

BACKGROUND

Although pathogenic 22q11.2 deletions are an important cause of developmental delays and lifelong disease burden, their variable and complex clinical expression contributes to under-recognition, delayed molecular diagnosis and uncertainty about prevalence. We sought to estimate the contemporary live-birth prevalence of typical 22q11.2 deletions using a population-based newborn screening sample and to examine data available for associated clinical features.

METHODS

Using DNA available from an unbiased sample of about 12% of all dried blood spots collected for newborn screening in Ontario between January 2017 and September 2018, we prospectively screened for 22q11.2 deletions using multiplex quantitative polymerase chain reaction assays and conducted independent confirmatory studies. We used cross-sectional analyses to compare available clinical and T-cell receptor excision circle (TREC, used in newborn screening for severe combined immunodeficiency) data between samples with and without 22q11.2 deletions.

RESULTS

The estimated minimum prevalence of 22q11.2 deletions was 1 in 2148 (4.7 per 10 000) live births (95% confidence interval [CI] 2.5 to 7.8 per 10 000), based on a total of 30 074 samples screened, with 14 having confirmed 22q11.2 deletions. Of term singletons, samples with 22q11.2 deletions had significantly younger median maternal age (25.5 v. 32.0 yr, difference -6.5 yr, 95% CI -7 to -2 yr), a greater proportion with small birth weight for gestational age (odds ratio 7.00, 95% CI 2.36 to 23.18) and lower median TREC levels (108.9 v. 602.5 copies/3 μL, p < 0.001).

INTERPRETATION

These results indicate that the 22q11.2 deletion syndrome is one of the most common of rare genetic conditions and may be associated with relatively younger maternal ages and with prenatal growth abnormalities. The findings support the public health importance of early - prenatal and neonatal - diagnosis that would enable prompt screening for and management of well-known actionable features associated with 22q11.2 deletions.

SCID newborn screening: What we've learned

Newborn screening for severe combined immunodeficiency, the most profound form of primary immune system defects, has long been recognized as a measure that would decrease morbidity and improve outcomes by helping patients avoid devastating infections and receive prompt immune-restoring therapy. The T-cell receptor excision circle test, developed in 2005, proved to be successful in pilot studies starting in the period 2008 to 2010, and by 2019 all states in the United States had adopted versions of it in their public health programs. Introduction of newborn screening for severe combined immunodeficiency, the first immune disorder accepted for population-based screening, has drastically changed the presentation of this disorder while providing important lessons for public health programs, immunologists, and transplanters.

TREC Screening for WHIM Syndrome

PURPOSE

T cell receptor excision circle (TREC) quantification is a recent addition to newborn screening (NBS) programs and is intended to identify infants with severe combined immunodeficiencies (SCID). However, other primary immunodeficiency diseases (PID) have also been identified as the result of TREC screening. We recently reported a newborn with a low TREC level on day 1 of life who was diagnosed with WHIM (warts, hypogammaglobulinemia, infections, myelokathexis) syndrome, a non-SCID primary immunodeficiency caused by mutations in the chemokine receptor CXCR4.

METHODS

We have now retrospectively reviewed the birth and clinical histories of all known WHIM infants born after the implementation of NBS for SCID.

RESULTS

We identified six infants with confirmed WHIM syndrome who also had TREC quantification on NBS. Three of the six WHIM infants had low TREC levels on NBS. All six patients were lymphopenic but only one infant had a T cell count below 1,500 cells/μL. The most common clinical manifestation was viral bronchiolitis requiring hospitalization. One infant died of complications related to Tetralogy of Fallot, a known WHIM phenotype.

CONCLUSION

The results suggest that WHIM syndrome should be considered in the differential diagnosis of newborns with low NBS TREC levels.

TRIAL REGISTRATION

Not applicable.

Hypocalcemia and a Positive Metabolic Screen for Severe Combined Immunodeficiency in an 11-Day-Old Male With DiGeorge Syndrome

22q11 deletion syndrome (22q11DS), also known as DiGeorge syndrome or velocardiofacial syndrome, is the most common human genetic microdeletion. Hypocalcemia secondary to hypoparathyroidism is a common finding in this condition and may present with seizures. We describe a case of an 11-day-old male presenting with hypocalcemic seizures and a positive newborn screen for severe combined immunodeficiency as the primary manifestations of 22q11DS. Given the potential for wide phenotypic variability, clinicians should maintain a high index of suspicion for this syndrome, especially in the neonate presenting with hypocalcemia.

Nonsevere combined immunodeficiency T-cell lymphopenia identified through newborn screening

PURPOSE OF REVIEW

Although severe combined immunodeficiency (SCID) is the primary target condition for newborn screening (NBS), over 25 secondary targets, conditions other than SCID, have been identified. There is no standard method for evaluating neonates with non-SCID T-cell lymphopenia (TCL) and no standard approaches to treatment. We will describe these conditions and discuss recommendations for evaluating and follow-up of non-SCID TCL detected by NBS.

RECENT FINDINGS

The birth prevalence of non-SCID TCL detected through SCID NBS is higher than SCID and can be a burden on NBS programs. We will present some publications discussing outcomes and comorbidities in these patients.

SUMMARY

NBS for SCID has been very successful in identifying infants with SCID at birth to institute early life saving therapies. TCL due to other conditions can cause significant immune deficiency and treatment is dependent on the cause of the defect, as well as the magnitude of the immunodeficiency. Data collection from NBS programs should include assessment of various therapies and clinical outcomes. Better systems for recording long-term outcomes of SCID NBS including both SCID and non-SCID conditions should become a priority for NBS programs. This will help to advance the goal of NBS programs: improve outcomes in the most cost-effective manner.

Candidate modifier genes for immune function in 22q11.2 deletion syndrome

Background

The 22q11.2 deletion syndrome (22q11.2DS) is the most common contiguous microdeletion affecting humans and exhibits extreme phenotypic heterogeneity. Patients can manifest any combination of comorbidities including congenital heart disease, hypoparathyroidism, cleft palate, kidney abnormalities, neurodevelopmental disorders, and immune dysfunction. Immunodeficiency is present in the majority of patients with 22q11.2DS and is the second leading cause of death in these patients. Knowing the genetic determinants of immune dysfunction will aid in prognostication and potentially novel treatments.

Methods

We performed exome sequencing and gene‐based variant association analysis on 31 deeply phenotyped individuals with the canonical 3Mb 22q11.2 deletion to identify what genes outside the 22q11.2 locus may be modifying the immune dysregulated phenotype. Immunophenotyping was performed using preexisting medical data and a novel scoring system developed from numerous clinical laboratory values including immunoglobulin levels, lymphocyte transformation to antigens (LTA), lymphocyte transformation to mitogens (LTM), and peripheral blood flow cytometry. Immunophenotypic scoring was validated against newborn screening T‐cell receptor excision circle (TREC) results.

Results

Rare DNA variants in transcriptional regulators involved in retinoic acid signaling (NCOR2, OMIM *600848 and EP300, OMIM *602700) were found to be associated with immunophenotype.

Conclusion

The expression of TBX1, which seems to confer the major phenotypic features of 22q11.2DS, is regulated via retinoic acid signaling, and alterations in retinoic acid signaling during embryonic development can lead to phenocopies of 22q11.2DS. These observations support the hypothesis that genetic modifiers outside the microdeletion locus may influence the immune function in 22q11.2DS patients.

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.

Identification of 22q11.2 deletion syndrome via newborn screening for severe combined immunodeficiency. Two years' experience in Catalonia (Spain)

BACKGROUND

The current scenario of newborn screening is changing as DNA studies are being included in the programs of several countries. Severe combined immunodeficiency (SCID) disorders can be detected using quantitative PCR assays to measure T-cell receptor excision circles (TRECs), a byproduct of correct T-cell development. However, in addition to SCID, other T-cell-deficient phenotypes such as 22q11.2 deletion syndrome 22q11.2 duplication syndrome, CHARGE syndrome, and trisomy 21 are detected.

METHODS

We present our experience with the detection of 22q11.2 deletion syndrome and 22q11.2 duplication syndrome in a series of 103,903 newborns included in the newborn screening program of Catalonia (Spain).

RESULTS

Thirty newborns tested were positive (low TREC levels) and five were found to have copy number variations at the 22q11 region (4 deletions and 1 duplication) when investigated with array comparative genomic hybridization technology and MLPA.

CONCLUSION

Newborn screening for SCID enables detection of several conditions, such as 22q syndromes, which should be managed by prompt, proactive approaches with adequate counseling for families by a multidisciplinary team.

A Cost-Effectiveness Analysis of Newborn Screening for Severe Combined Immunodeficiency in the UK

Severe combined immunodeficiency (SCID) can be detected through newborn bloodspot screening. In the UK, the National Screening Committee (NSC) requires screening programmes to be cost-effective at standard UK thresholds. To assess the cost-effectiveness of SCID screening for the NSC, a decision-tree model with lifetable estimates of outcomes was built. Model structure and parameterisation were informed by systematic review and expert clinical judgment. A public service perspective was used and lifetime costs and quality-adjusted life years (QALYs) were discounted at 3.5%. Probabilistic, one-way sensitivity analyses and an exploratory disbenefit analysis for the identification of non-SCID patients were conducted. Screening for SCID was estimated to result in an incremental cost-effectiveness ratio (ICER) of £18,222 with a reduction in SCID mortality from 8.1 (5-12) to 1.7 (0.6-4.0) cases per year of screening. Results were sensitive to a number of parameters, including the cost of the screening test, the incidence of SCID and the disbenefit to the healthy at birth and false-positive cases. Screening for SCID is likely to be cost-effective at £20,000 per QALY, key uncertainties relate to the impact on false positives and the impact on the identification of children with non-SCID T Cell lymphopenia.

Noninvasive screening by cell-free DNA for 22q11.2 deletion: Benefits, limitations, and challenges

Cell-free DNA (cfDNA) testing for fetal aneuploidy is one of the most important technical advances in prenatal care. Additional chromosome targets beyond common aneuploidies, including the 22q11.2 microdeletion, are now available because of this clinical testing technology. While there are numerous potential benefits, 22q11.2 microdeletion screening using cfDNA testing also presents significant limitations and pitfalls. Practitioners who are offering this test should provide comprehensive pretest and posttest prenatal counselling. The discussion should include the possibility of an absence of a result, as well as the risk of possible discordance between cfDNA screening results and the actual fetal genetic chromosomal constitution. The goal of this review is to provide an overview of the cfDNA testing technologies for 22q11.2 microdeletions screening, describe the current state of test validation and clinical experience, review "no results" and discordant findings based on differing technologies, and discuss management options.

Detecting 22q11.2 Deletion Syndrome in Newborns with Low T Cell Receptor Excision Circles from Severe Combined Immunodeficiency Screening

OBJECTIVE

Based on experiences and results from newborn screening for severe combined immunodeficiency (SCID), we evaluated the occurrence of chromosome 22q11.2 deletion syndrome (22q11.2DS) in newborns with different T cell receptor excision circles (TREC) results and established a second tier genetic test for 22q11.2DS.

STUDY DESIGN

Recalled dried blood spots from 486 newborns with TREC results <90 copies/uL were tested from the SCID newborn screening. Quantitative real-time polymerase chain reaction assay was used to detect the copy number of TBX1 and HIRA genes by simple DNA extraction method. Multiplex ligation dependent probe amplification was used for further confirmation.

RESULTS

Four hundred sixty-eight cases were considered negative because their haploid copy number of TBX1 and HIRA genes was >0.75. Eighteen cases with TBX1 and/or HIRA gene copy number <0.75 were suspected as positive, and 13 cases were further confirmed with 22q11.2DS. Detection rates of 22q11.2DS were 10.7% (6/56) in TREC <30 copies, 6.8% (9/132) in <50 TREC copies, 4.6% (12/260) in <70 TREC copies, and 2.7% (13/486) in <90 TREC copies.

CONCLUSIONS

22q11.2DS detection can be incorporated into the second-tier assay in subjects with low TREC copies in SCID screening. The dried blood spot methods were feasible for 22q11.2DS newborn screening.

Immune and Genetic Features of the Chromosome 22q11.2 Deletion (DiGeorge Syndrome)

PURPOSE OF REVIEW

This review provides an update on the progress in identifying the range of immunological dysfunction seen in DiGeorge syndrome and on more recent diagnostic and treatment approaches.

RECENT FINDINGS

Clinically, the associated thymic hypoplasia/aplasia is well known and can have profound effects on T cell function. Further, the humoral arm of the immune system can be affected, with hypogammaglobulinemia and poor vaccine-specific antibody response. Additionally, genetic testing utilizing chromosomal microarray demonstrates a small but significant number of 22q11 deletions that are not detectable by standard FISH testing. The recent addition of a TREC assay to newborn screening can identify a subset of infants whose severe immune defects may result from 22q11 deletion. This initial presentation now also places the immunologist in the role of "first responder" with regard to diagnosis and management of these patients. DiGeorge syndrome reflects a clinical phenotype now recognized by its underlying genetic diagnosis, chromosome 22q11.2 deletion syndrome, which is associated with multisystem involvement and variable immune defects among patients. Updated genetic and molecular techniques now allow for earlier identification of immune defects and confirmatory diagnoses, in this disorder with life-long clinical issues.

Newborn Screening for Severe Combined Immunodeficiency

PURPOSE OF REVIEW

This review provides a brief history of newborn screening (NBS) for severe combined immunodeficiency (SCID), discusses the theoretical basis for the T cell receptor excision circle (TREC) assay, highlights the results of recent studies using the TREC, and provides practical advice for the evaluation of infants with an abnormal TREC assay.

RECENT FINDINGS

Currently, all but three states perform NBS for SCID in the USA. NBS using the TREC assay is highly sensitive in identifying infants with SCID and may also identify infants with T cell lymphopenia due to other causes such as congenital syndromes, multiple congenital anamolies, and some combined immunodeficiencies. Regardless of the genetic etiology, all forms of SCID are characterized by a severe deficiency of naïve T cells. TRECs are a biomarker of newly formed, naïve T cells that have recently left the thymus. Consequently, the TREC assay identifies infants with SCID and other causes of severe T cell lymphopenia.

First Year of Israeli Newborn Screening for Severe Combined Immunodeficiency-Clinical Achievements and Insights

Severe combined immunodeficiency (SCID), the most severe form of T cell immunodeficiency, is detectable through quantification of T cell receptor excision circles (TRECs) in dried blood spots obtained at birth. Herein, we describe the results of the first year of the Israeli SCID newborn screening (NBS) program. This important, life-saving screening test is available at no cost for every newborn in Israel. Eight SCID patients were diagnosed through the NBS program in its first year, revealing an incidence of 1:22,500 births in the Israeli population. Consanguine marriages and Muslim ethnic origin were found to be a risk factor in affected newborns, and a founder effect was detected for both IL7Rα and DCLRE1C deficiency SCID. Lymphocyte subset analysis and TREC quantification in the peripheral blood appear to be sufficient for confirmation of typical and leaky SCID and ruling out false positive (FP) results. Detection of secondary targets (infants with non-SCID lymphopenia) did not significantly affect the management or outcomes of these infants in our cohort. In the general, non-immunodeficient population, TREC rises along with gestational age and birth weight, and is significantly higher in females and the firstborn of twin pairs. Low TREC correlates with both gestational age and birth weight in extremely premature newborns. Additionally, the rate of TREC increase per week consistently accelerates with gestational age. Together, these findings mandate a lower cutoff or a more lenient screening algorithm for extremely premature infants, in order to reduce the high rate of FPs within this group. A significant surge in TREC values was observed between 28 and 30 weeks of gestation, where median TREC copy numbers rise by 50% over 2 weeks. These findings suggest a maturational step in T cell development around week 29 gestation, and imply moderate to late preterms should be screened with the same cutoff as term infants. The SCID NBS program is still in its infancy, but is already bearing fruit in the early detection and improved outcomes of children with SCID in Israel and other countries.