T Cell Receptor Excision Circle Screening Research Articles

Evolving Patterns in Inpatient Pediatric Consultations to Allergy/Immunology at an Academic Medical Center

Background: Consultations to pediatric allergy/immunology are of benefit to many hospitalized inpatients, but there is limited current information about how T-cell receptor excision circles (TREC) screening may have changed these patterns for pediatric populations. We aimed to determine the types of consults being requested and their relative frequencies for primary pediatric allergy/immunology consults under an academic fellowship program since the start of TREC screening in 2016. Information gained could help identify focal concepts for pediatric allergy inpatient training curricula for fellowship and graduate medical education programs. Methods: Under an IRB approved study of an academic allergy fellowship consultation log, we retrospectively reviewed electronic medical records of pediatric allergy and immunology consults and categorized consultations by their primary indication. Results: Three-hundred and eighty-three pediatric allergy/immunology consultations were seen between September 4, 2016 to November 24, 2022. In terms of frequency, the most common consultation was for immunodeficiency evaluation or treatment, n=205 (53.5%), followed by drug allergy n=55 (14.4%), general allergy concerns n=43 (11.2%), skin allergy n=35 (9.1%), and less commonly inflammatory syndromes, n=26 (6.8%) and food allergy, n=19 (5.0%). Questions related to TREC screening comprised 21% of all immunodeficiency consults, at n=43. Conclusion: At an academic allergy center where all allergy/immunology service lines are currently provided, the most common reason for pediatric consultations were for help with immunodeficiency evaluation/treatment and drug allergy. TREC screening is a new key indication for consultation. Fellowship programs may benefit from focusing on these content areas for the pediatric inpatient setting.

Screening newborns for low T cell receptor excision circles (TRECs) Fails to Detect Immunodeficiency, Centromeric Instability, and Facial Anomalies Syndrome.

Assessment of T-cell receptor excision circles (TRECs) in dried blood spots of newborns allows the detection of severe combined immunodeficiency (SCID) (T cells <300/μL at birth) with a presumed sensitivity of 100%. TREC screening also identifies patients with selected combined immunodeficiency (CID) (T cells >300/μL, yet <1500/μL at birth). Nevertheless, relevant CIDs that would benefit from early recognition and curative treatment pass undetected. We hypothesized that TREC screening at birth cannot identify CIDs that develop with age. We analyzed the number of TRECs in dried blood spots in archived Guthrie cards of 22 children who had been born in the Berlin-Brandenburg area between January 2006 and November 2018 and who had undergone hematopoietic stem-cell transplantation (HSCT) for inborn errors of immunity. All patients with SCID would have been identified by TREC screening, but only 4 of 6 with CID. One of these patients had immunodeficiency, centromeric instability, and facial anomalies syndrome type 2 (ICF2). Two of 3 patients with ICF whom we have been following up at our institution had TREC numbers above the cutoff value suggestive of SCID at birth. Yetall patients with ICF had a severe clinical course that would have justified earlier HSCT. In ICF, naïve T cells may be present at birth, yet they decline with age. Therefore, TREC screening cannot identify these patients. Early recognition is nevertheless crucial, as patients with ICF benefit from HSCT early in life.

Postnatal corticosteroid treatment as a risk factor for false positivity in severe combined immunodeficiency newborn screening.

From 2011, 37 children were referred to a hospital due to low levels of T cell receptor excision circles (TRECs) from newborn screening. Among them, three children were immunologically characterized and followed up to show that postnatal corticosteroid usage may be among the causes of false positivity in TRECs screening.

Delayed onset ADA-SCID presenting as secondary HLH in a patient with normal newborn screening

Severe combined immunodeficiency (SCID) is a rare genetic syndrome caused by aberrant immune cell development or function and is fatal without early identification and treatment. The Centers for Disease Control estimates the annual incidence of SCID to be one case per 40,000 to 100,000 live births. Newborn screening using T-cell receptor excision circles (TREC) allows for early detection and timely treatment of SCID. Adenosine deaminase (ADA) is a vital enzyme in the purine salvage pathway, and its deficiency results in disruption of T, B and NK cell development, accounting for 10–20% of SCID cases. The timing of ADA-SCID presentation ranges from birth to delayed onset disease. Importantly, without early recognition and treatment, delayed onset ADA-SCID results in accumulation of toxic metabolites causing immune dysfunction, recurrent infections, and subsequent organ damage. Recently, some groups have questioned whether traditional TREC newborn screening adequately identifies ADA-SCID, especially those cases with delayed onset. We present the case of a 2-year-old male with normal newborn screening but a history of recurrent otitis media and respiratory infections who developed multisystem organ failure and septicemia with Escherichia coli, candida, adenovirus and enterovirus despite broad-spectrum antimicrobials. The patient also had features of a hyperinflammatory syndrome with fever, pancytopenia, hypertriglyceridemia, and hyperferritinemia and was treated for hemophagocytic lymphohistiocytosis (HLH) with dexamethasone and plasma exchange followed by anakinra, etoposide, and emapalumab. The patient was maximally supported with mechanical ventilation, extracorporeal membrane oxygenation, and renal replacement therapy but had progressive clinical deterioration and ultimately expired. Autopsy was notable for thymic aplasia and erythrophagocytosis in the bone marrow and lymph nodes. Genetic testing revealed a heterozygous missense pathogenic variant in exon 7 in the ADA gene as well as novel heterozygous intronic variant of unknown significance in the ADA gene. Postmortem data suggests this patient had ADA-SCID with multi-pathogen infections and secondary HLH. This case potentially identifies a novel pathogenic variant in ADA missed by traditional TREC newborn screening and highlights the need to retain a high clinical suspicion of SCID in patients with a history of recurrent infections despite normal TREC screening.

Premature Infants Have Normal Maturation of the T Cell Receptor Repertoire at Term.

Premature infants are known to have immature immune systems compared to term infants; however, the impacts of ex utero immune development are not well characterized. Our previous retrospective clinical review showed prolonged T cell lymphopenia in a subset of extremely premature infants, suggesting that they may have lasting abnormalities in their T cell compartments. We used T cell receptor (TCR) repertoire sequencing to analyze the composition of the T cell compartment in premature and term infants in our NICU. We collected twenty-eight samples from individual subjects and analyzed the number of clonotypes, repertoire diversity, CDR3 length, and V gene usage between groups based on gestational age at birth and postmenstrual age at the time of sample collection. Further, we examined the TCR repertoire in infants with severe bronchopulmonary dysplasia (BPD) and those with abnormal T cell receptor excision circle (TREC) assays. Former extremely premature infants who were corrected to term postmenstrual age had TCR repertoire diversity that was more similar to term born infants than extremely premature infants, supporting normal maturation of the repertoire. Infants with severe BPD did not appear to have increased abnormalities in repertoire diversity. Decreased TCR repertoire diversity was associated with repeatedly abnormal TREC screening, although the diversity was within the normal range for subjects without low TRECs. This study suggests that extremely premature infants demonstrate normal maturation of the T cell repertoire ex utero. Further work is needed to better characterize postnatal T cell development and function in this population.

TREC Screening for WHIM Syndrome.

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. We have now retrospectively reviewed the birth and clinical histories of all known WHIM infants born after the implementation of NBS for SCID. 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 sixpatients were lymphopenic but only one infant had a T cell count below 1,500 cells/μL. The most commonclinical manifestation was viral bronchiolitis requiring hospitalization. One infant died of complications related toTetralogy of Fallot, a known WHIM phenotype. The results suggest that WHIM syndrome should be considered in the differential diagnosis of newborns with low NBS TREC levels. Not applicable.

Newborn Screening through TREC, TREC/KREC System for Primary Immunodeficiency with limitation of TREC/KREC. Comprehensive Review.

Newborn screening (NBS) by quantifying T cell receptor excision circles (TRECs) and Kappa receptor excision circles in neonatal dried blood spots (DBS) enables early diagnosis of different types of primary immune deficiencies. Global newborn screening for PID, using an assay to detect T-cell receptor excision circles (TREC) in dried blood spots (DBS), is now being performed in all states in the United States. In this review, we discuss the development and outcomes of TREC, TREC/KREC combines screening, and continued challenges to implementation. To review the diagnostic performance of published articles for TREC and TREC/ KREC based NBS for PID and its different types. Different research resources were used to get an approach for the published data of TREС and KREC based NBS for PID like PubMed, Scopus, Google Scholar, Research gate EMBASE. We extracted TREC and KREC screening Publisher with years of publication, content and cut-off values, and a number of retests, repeat DBS, and referrals from the different published pilot, pilot cohort, Case series, and cohort studies. We included the results of TREC, combined TREC/KREC system based NBS screening from different research articles, and divided these results between the Pilot studies, case series, and cohort. For each of these studies, different parameter data are excluded from different articles. Thirteen studies were included, re-confirming 89 known SCID cases in case series and reporting 53 new SCID cases in 3.15 million newborns. Individual TREC contents in all SCID patients were <25 TRECs/μl (except in those evaluated with the New York State assay). TREC and KREC sensitivity for typical SCID and other types of PID was 100 %. It shows its importance and anticipating the significance of implementation in different undeveloped and developed countries in the NBS program in upcoming years. Data adapting the screening algorithm for pre-term/ill infants reduce the amount of false-positive test results.

Multiplex PCR-Based Newborn Screening for Severe T and B-Cell Lymphopenia: The first Pilot Study in Turkey.

Objectives:Severe combined immunodeficiency disease (SCID), non-SCID T-cell lymphopenia, and other primary immunodeficiency diseases with T-cell and B-cell lymphopenia have low the T-cell-receptor-excision circles (TRECs) and κ-deleting-recombination-excision circles (KRECs) levels that can be measured in dried blood spots (DBS) of the newborn. The incidence of SCID and non-SCID T-cell lymphopenia in Western societies has been reported by TREC screening of newborns as 1: 58,000 and 1: 7300, respectively. Since there is no similar study in our country, we aimed to perform the first pilot study of TREC and KREC screening of newborn for SCID and non-SCID T-cell lymphopenia in Turkey.Methods:The heel blood samples of newborns born between 1st October 2015 and 31st December 2016 at two major hospitals in our city were included in this study. TREC and KREC copies were determined by a multiplex quantitative PCR-based method from newborn DBS. Cutoff levels were used as 7 copies per DBS for TRECs and KRECs, 1000 copies for ACTB (internal control). Failed samples or abnormal results in measurements were tested the second time. An immunologist evaluated data of newborns with low TREC and KREC copies clinically and through the laboratory.Results:A total of 1960 DBS were tested. The results of 1856 newborns were evaluated. The low TRECs and/or KRECs levels were detected in 71 newborns (3.8 %). The low TRECs rate was 1.1 %. Preterm newborns have lower levels of TRECs and KRECs than term newborns (both p <0.0001). As a result of immunological research, we did not detect any SCID, but we detected 2 newborns with non-SCID T-cell lymphopenia (1:928). These 2 newborns were found to have frequent and severe infectious diseases or hypogammaglobulinemia in their clinical follow-up, although they did not have absolute lymphopenia.Conclusion:Non-SCID T-cell lymphopenia is common in our country than in western societies. TRECs and KRECs assay should be considered for routine NBS programs in our country. Studies involving more newborns should be conducted to detect SCID.

Universal Newborn Screening for Severe Combined Immunodeficiency (SCID).

Patients with severe combined immunodeficiency (SCID) are born with profound deficiency of functional T-lymphocytes. Early detection and diagnosis would allow for prompt institution of isolation from infection and referral for definitive treatment with allogeneic hematopoietic stem cell transplantation. Universal newborn screening for SCID, using an assay to detect T-cell receptor excision circles (TREC) in dried blood spots (DBS), is now being performed in all states in the United States. In this review, we discuss the development and outcomes of TREC screening, and continued challenges to implementation.

ABNORMAL TRECS AND SEVERE LYMPHOPENIA SECONDARY TO MATERNAL USE OF AZATHIOPRINE

Introduction T-cell receptor excision circles (TREC) analysis is an important addition to the newborn screen (NBS) for early identification of primary immune deficiency disorders (PID), specifically severe combined immune deficiency (SCID). TREC screening has also identified T-cell lymphopenias secondary to causes not associated with PID. Our case illustrates a neonate whose profound lymphopenia was likely caused by in-utero exposure to an immunomodulatory medication. Case Description A term male infant, born to a mother on azathioprine for systemic erythematous lupus, was referred for abnormal TRECs on NBS. Flow cytometry revealed marked lymphopenia affecting T, B and NK cell lines (338/mm3, 1/mm3 and 9/mm3, respectively). Flow cytometry showed 56% CD3/CD4/RA+ cells, higher than expected in SCID, yet below normal for age. Repeat flow cytometry one week later demonstrated slightly improved CD3/4/8 counts, ongoing severe B cell lymphopenia, with normalization of NK cell counts. Genetic testing for 207 known PID mutations was non-diagnostic. Three weeks later, B-cell counts normalized, and T-cell counts dramatically improved. Placental transfer of azathioprine was felt to be responsible for the previous lab abnormalities. Discussion In addition to SCID, transient T-cell lymphopenias of unclear clinical significance are identified by TREC screening. It remains uncertain which of these patients warrant further work up, and infants and their families may be subject to unnecessary testing and emotional stress. This case is a reminder that the family medical history is crucial in identifying possible secondary causes of abnormal TRECs. It also raises demonstrates the potential impact of maternal immunosuppression on infant hematopoiesis.

Narrative review of severe combined immunodeficiency—a purine metabolism disorder

Severe combined immunodeficiency (SCID) is a primary immune deficiency that is a pediatric emergency. Left untreated, patients will die prior to 2 years of age from overwhelming infection. There are many known causes of SCID, but this review focuses on adenosine deaminase (ADA) deficiency. ADA is a ubiquitous “housekeeping” enzyme, and its deficiency leads to buildup of toxic metabolites, which preferentially affects lymphocytes but also causes non-immune manifestations of disease. While previously diagnosed based on recurrent, severe, or unusual infection, SCID is now being diagnosed during its initial asymptomatic period thanks to recent implementation of T cell receptor excision circle (TREC) newborn screening, thus greatly improving survival of patients as treatment can occur before the onset of infection. To date, TREC screening has shown 100% sensitivity for SCID but also has brought to light other causes of T cell lymphopenia that were previously lesser known. ADA-deficient SCID can be treated through enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), or gene therapy, and advances continue to be made every day that improve cost-effectiveness and efficacy of these therapies and make them more widely available to patients.

Diagnostic Challenges in the Era of Genomic Sequencing and Newborn Screening

Early diagnosis of rare immune disorders is important for clinical care and of great interest for the study of immune pathways. Severe combined immunodeficiency (SCID) is a collective term for the most profound inherited defects of T cell development combined with B cell defects or dysfunction. While fatal without treatment, SCID is treatable by allogeneic hematopoietic cell transplantation, or in certain genotypes by enzyme or gene therapy. Avoidance of life-threatening infections to provide optimal treatment and outcomes for affected infants has led to population-based SCID newborn screening (NBS). Infants with SCID fail to generate a diverse repertoire of functional T cells, and consequently have very low numbers of T cells and T cell receptor excision circles (TRECs), DNA byproducts of T cell receptor gene rearrangement. TRECs are readily measured in DNA isolated from newborn dried blood spots (DBS) collected for population based screening. Thus newborn screening for insufficient TRECs identifies SCID before infections occur. As SCID NBS has become widespread, new disease definitions are required for healthy-appearing affected infants without failure to thrive or opportunistic infections. Typical SCID cases have <300 autologous T cells/uL, <10% of the lower range of normal proliferation to the mitogen phytohemmaglutinin A, and/or detectable maternal T cell engraftment, most often with deleterious mutations in recognized SCID genes. One fourth of all SCID cases are “leaky” due to hypomorphic SCID gene mutations; these cases are also detected by TREC testing; they may have >300 T cells/uL, but have impaired T cell function and lack naïve CD4 T cells expressing CD45RA. A subset of infants with leaky SCID have Omenn syndrome, with expansion of oligoclonal, dysregulated T cells leading to adenopathy, erythroderma, hepatosplenomegaly, eosinophilia, and elevated IgE. In addition to these primary target disorders of population screening for SCID, the TREC test identifies infants with additional conditions due to either impaired production or increased loss of T cells. Non-SCID congenital syndromes with variable degrees of T cell lymphopenia (TCL) include DiGeorge syndrome/22q11.2 deletion, CHARGE syndrome, trisomy 21, and ataxia telangiectasia, among others. TREC NBS also finds infants with secondary TCL, in which T cell generating capacity is intrinsically normal, but circulating T cells are diminished as a consequence of other factors, including hydrops, congenital heart disease, chylothorax, neonatal leukemia, maternal immunosuppressive medications taken during pregnancy, or extreme preterm birth. The T cells of these infants normalize once their primary problems resolve. A particularly challenging group of infants are those with abnormal TREC screen results and non-SCID TCL, but no immediate diagnosis. About half of these have syndromes, such as DiGeorge/22q deletion, but with mild or initially unapparent features; others experience resolution of TCL over time, while still others prove to have previously unknown immune disorders that may be diagnosed after deep sequencing and research functional studies. It is important to remember that many serious disorders of T cells are not identified by TREC screening if the block in T cell development or function occurs at a later stage than T cell receptor rearrangement; combined immunodeficiencies (CIDs) with TRECs that are often normal include Zap-70 deficiency and MHC class I and II non-expression. Thus, while virtually completely sensitive and highly specific for the intended target, SCID, population based TREC screening leaves us with both diagnostic dilemmas presented by non-symptomatic infants with low T cells and inability to capture individuals with the >300 non-SCID primary immunodeficiency disorders that would also benefit from early intervention. Deep sequencing is not yet clinically useful, not only due to cost, turnaround time and technical limitations, but primarily due to problems of interpretation, given the extraordinary number of genomic variants of uncertain significance. DisclosuresPuck:InVitae, a clinical DNA sequencing company: Other: Spouse employment and stock options; UpToDate: Patents & Royalties: Recieve royalties to write and edit entries on primary immune disorders.

Newborn Screening for Primary Immunodeficiency Diseases: The Past, the Present and the Future

Primary immunodeficiency diseases (PID) are a heterogeneous group of disorders caused by inborn errors of immunity, with affected children presenting with severe, recurrent or unusual infections. Over 300 distinct genetic molecular abnormalities resulting in PID have been identified, and this number continues to rise. Newborn screening for PID has been established in many countries, with the majority of centers using a PCR-based T cell receptor excision circle (TREC) assay to screen for severe combined immunodeficiency (SCID) and other forms of T cell lymphopenia. Multiplexed screening including quantitation of kappa-recombining exclusion circles (KREC) has also been described, offering advantages over TREC screening alone. Screening technologies are also expanding to include protein-based assays to identify complement deficiencies and granulocyte disorders. Given the rapid advances in genomic medicine, a potential future direction is the application of next-generation sequencing (NGS) technologies to screen infants for a panel of genetic mutations, which would enable identification of a wide range of diseases. However, several ethical and economic issues must be considered before moving towards this screening strategy.

Newborn Screening for Severe Primary Immunodeficiency Diseases in Sweden\u2014a 2-Year Pilot TREC and KREC Screening Study

Newborn screening for severe primary immunodeficiencies (PID), characterized by T and/or B cell lymphopenia, was carried out in a pilot program in the Stockholm County, Sweden, over a 2-year period, encompassing 58,834 children. T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) were measured simultaneously using a quantitative PCR-based method on DNA extracted from dried blood spots (DBS), with beta-actin serving as a quality control for DNA quantity. Diagnostic cutoff levels enabling identification of newborns with milder and reversible T and/or B cell lymphopenia were also evaluated. Sixty-four children were recalled for follow-up due to low TREC and/or KREC levels, and three patients with immunodeficiency (Artemis-SCID, ATM, and an as yet unclassified T cell lymphopenia/hypogammaglobulinemia) were identified. Of the positive samples, 24 were associated with prematurity. Thirteen children born to mothers treated with immunosuppressive agents during pregnancy (azathioprine (n = 9), mercaptopurine (n = 1), azathioprine and tacrolimus (n = 3)) showed low KREC levels at birth, which spontaneously normalized. Twenty-nine newborns had no apparent cause identified for their abnormal results, but normalized with time. Children with trisomy 21 (n = 43) showed a lower median number of both TREC (104 vs. 174 copies/μL blood) and KREC (45 vs. 100 copies/3.2 mm blood spot), but only one, born prematurely, fell below the cutoff level. Two children diagnosed with DiGeorge syndrome were found to have low TREC levels, but these were still above the cutoff level. This is the first large-scale screening study with a simultaneous detection of both TREC and KREC, allowing identification of newborns with both T and B cell defects.

Higher prevalence of immune deficiency syndrome found in infants: study finds nearly twice as many newborns affected by severe combined immunodeficiency than previous research had estimated.

Higher prevalence of immune deficiency syndrome found in infants: study finds nearly twice as many newborns affected by severe combined immunodeficiency than previous research had estimated.

Newborn screening for severe T and B cell lymphopenia identifies a fraction of patients with Wiskott–Aldrich syndrome

The lack or marked reduction of recently formed T and B cells provides a basis for neonatal screening for severe combined immunodeficiencies (SCID) and X-linked agammaglobulinemia (XLA). Newborns with other conditions are also identified if a severe T or B cell lymphopenia is present at birth. We retrospectively analyzed Guthrie card samples from 11 children with Wiskott–Aldrich syndrome (WAS), a rare disease that requires early diagnosis and treatment, to determine whether combined T-cell receptor excision circle (TREC) and kappa-deleting recombination excision circle (KREC) screening could identify these patients. 4 of 11 patients showed markedly reduced TREC or KREC copy numbers in their DBS as compared to storage-time matched controls and prospectively screened Swedish and German newborns. No correlation was observed between the WAS gene mutations, the clinical severity/course and the result of the screening assay. A diagnosis of WAS should thus be considered in newborns with positive TREC or KREC screening results.

Retrospective Analysis of TREC Based Newborn Screening Results and Clinical Phenotypes in Infants with the 22q11 Deletion Syndrome

Population-based newborn screening using T-cell receptor excision circles (TREC) identifies infants with severe T-lymphopenia, seen in severe combined immunodeficiencies (SCID), but also infants with the 22q11 deletion syndrome (22q11DS). Methods for analysis of kappa-deleting recombination excision circles (KREC) help identifying infants with B-lymphopenia. We aimed to evaluate the occurrence of abnormal TREC or KREC newborn screening results in 22q11DS patients and assessed the clinical relevance of abnormal screening reports. Simultaneous TREC and KREC analysis was performed on stored original Guthrie cards. Patients with abnormal screening reports were compared to patients with normal reports, regarding lymphocyte counts and clinical severity, obtained by retrospective analysis of medical charts. Of 48 included patients, nine (19 %) had abnormal TREC copy numbers. All 22q11DS patients with abnormal TRECs had CD3+ T-lymphopenia at the time of diagnosis, but only one patient had the complete DiGeorge syndrome. Identified 22q11DS patients with abnormal TREC copy numbers showed significantly lower CD8+ T-lymphocytes at time-of-diagnosis and were significantly more prone to viral infections, compared to 22q11DS patients with normal TREC copy numbers. All 22q11DS patients showed KREC copies within the normal range. In this retrospective study a high proportion of 22q11DS patients were identified by TREC-based newborn screening. Although only one of them had the complete DiGeorge syndrome with no T-lymphocytes, all of them had T-lymphopenia and most of them had recurrent viral infections, as well as other medical problems, warranting early recognition of the syndrome.

Screening of Neonatal UK Dried Blood Spots Using a Duplex TREC Screening Assay

Severe Combined Immunodeficiency (SCID) is considered to be a paediatric emergency and unless identified promptly can be life-threatening. Frequently, infants are not diagnosed with SCID until they have become seriously ill with infection leading to treatment complications and a poorer prognosis. We aimed to test a newly available commercial duplex assay to measure T cell receptor excision circles (TRECs) to establish if this would be suitable for newborn screening for SCID in the UK. Over 5000 anonymous retrospective dried blood spots (DBS) were used alongside 18 confirmed SCID positive DBS with a newly available duplex assay to measure TRECs levels and control gene levels. We also included testing of premature babies and babies from neonatal intensive care units (NICU) as these have been shown to have high false positive rates in other TREC screening assays. All 18 SCID DBS samples were successfully identified as SCID positives in the study. The number of presumptive positives detected was dependent on the TREC cut-off threshold settings. When analysed with five different TRECs cut-off values (20, 25, 30, 35 and 40 TREC copies/μl blood) the presumptive positive rate ranged from 0.04 to 1.00 % of samples tested. Premature infants and neonates from NICU did not show high presumed false positive rates in this assay. The study demonstrated that this duplex assay kit will identify all newborns with SCID as presumptive positives. The data also shows that with suitable TREC cut-off settings the number of presumptive positives from non-SCID newborns will be manageable in the context of a national screening service.

Newborn Screening for SCID Identifies Patients with Ataxia Telangiectasia

PurposeSevere combined immunodeficiency (SCID) is characterized by failure of T lymphocyte development and absent or very low T cell receptor excision circles (TRECs), DNA byproducts of T cell maturation. Newborn screening for TRECs to identify SCID is now performed in several states using PCR of DNA from universally collected dried blood spots (DBS). In addition to infants with typical SCID, TREC screening identifies infants with T lymphocytopenia who appear healthy and in whom a SCID diagnosis cannot be confirmed. Deep sequencing was employed to find causes of T lymphocytopenia in such infants.MethodsWhole exome sequencing and analysis were performed in infants and their parents. Upon finding deleterious mutations in the ataxia telangiectasia mutated (ATM) gene, we confirmed the diagnosis of ataxia telangiectasia (AT) in two infants and then tested archival newborn DBS of additional AT patients for TREC copy number.ResultsExome sequencing and analysis led to 2 unsuspected gene diagnoses of AT. Of 13 older AT patients for whom newborn DBS had been stored, 7 samples tested positive for SCID under the criteria of California’s newborn screening program. AT children with low neonatal TRECs had low CD4 T cell counts subsequently detected (R = 0.64).ConclusionsT lymphocytopenia in newborns can be a feature of AT, as revealed by TREC screening and exome sequencing. Although there is no current cure for the progressive neurological impairment of AT, early detection permits avoidance of infectious complications, while providing information for families regarding reproductive recurrence risks and increased cancer risks in patients and carriers.

The Wisconsin approach to newborn screening for severe combined immunodeficiency

Severe combined immunodeficiency (SCID) is a life-threatening disease of infants that is curable with hematopoietic cell transplantation if detected early. Population-based screening for SCID using the T-cell receptor excision circle (TREC) assay began in Wisconsin in 2008; 5 infants with SCID or other formsof severe T-cell lymphopenia (TCL) have been detected, and no infants with SCID have been missed. This review will provide an overview of the TREC screening assay and an update of the findings from Wisconsin on all infants screened from January 1, 2008, until December 31, 2010. Importantly, we give practical recommendations regarding newborn population-based screening using the TREC assay, including the evaluation and care of infants detected.