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Background: Since the onset of the COVID-19 pandemic, a main challenge for clinicians and public health decision-makers has revolved around risk stratification in vulnerable populations, in particular individuals with inborn errors of immunity (IEI). However, available reports of the clinical course of COVID-19 in patients with IEI show wide variability, from a complete lack of symptoms to severe and complicated disease. Objective: To present the clinical features and outcomes of SARS-CoV-2 infection in adult patients with IEI. Methods: We performed a retrospective chart review documenting patient characteristics and clinical course of SARS-CoV-2 infection between December 2021 and July 2022. Results: Ten adult patients with IEI followed in our center were diagnosed with COVID-19, as determined by RT-PCR or rapid antigen testing. IEI in this cohort included those with humoral and combined immunodeficiencies, as well as phagocytic defects. An underlying lung comorbidity was identified in 3 patients. Symptoms were mostly mild and self-limiting, and no severe outcomes, complications, or mortality were noted in this study. Conclusions: We suggest that patients affected by a wide range of both humoral and combined IEI may demonstrate resilience, while highlighting the possible protective effects of vaccination and immunoglobulin replacement in this population. Statement of Novelty: We report on the mild COVID-19 clinical course of 10 adults with IEI.

Background: Forkhead-box protein N1 (FOXN1) plays a critical role in the proper development and function of thymic epithelial cells, required for T cell ontogeny. Homozygous variants in the FOXN1 gene, encoding FOXN1, cause severe combined immunodeficiency (SCID), whereas heterozygous mutations are associated with variable presentations and over time, improving T cell function. Aim: To highlight the importance of broader genetic investigations to attain a definitive molecular diagnosis following abnormal newborn screening for SCID. Methods: Case report of a patient with immunodeficiency due to a novel de novo FOXN1 mutation. Results: The patient was identified following abnormal newborn screening for SCID in which T cell receptor excision circles were absent/very low. Initial immune investigations revealed severe T cell lymphopenia and poor lymphocyte function and she was diagnosed with T-B+NK+SCID. During work-up for hematopoietic stem cell transplantation, extensive genetic investigations identified a novel heterozygous mutation in FOXN1. A more conservative management approach was taken, and over the following months, the patient’s immune parameters improved. Conclusion: Newborn screening for SCID has facilitated the detection of SCID, as well as other T cell immunodeficiencies, before infectious complications and organ damage occur. Heterozygous mutations in FOXN1 are associated with more variable presentations including improving immune indices with age. Here, results of genetic investigations were essential for informing the management of this case. Statement of Novelty: We report a novel heterozygous mutation in FOXN1, presenting initially as T-B+NK+ SCID with gradual improvement of immune parameters over time.

Introduction: DiGeorge syndrome is a heterogenous disorder with various clinical presentations. Common features include thymic hypoplasia, T cell lymphopenia, conotruncal heart defects, facial dysmorphism, cleft palate, developmental delay, and hypoparathyroidism. The severity of this condition varies, however typical presentation includes congenital heart defects and characteristic facial features. Isolated hypocalcemia in DiGeorge syndrome is rarely seen in neonates but rather as the sole manifestation in older teenagers or adults. Aim: To report a case of an atypical presentation of DiGeorge syndrome. Results: We report here a case of an infant who was diagnosed with DiGeorge syndrome, with seizures being the only clinical manifestation displayed by the patient. He was found to have low T cell receptor excision circle levels on a newborn screen (NBS) for severe combined immunodeficiency (SCID). He did not have facial dysmorphism nor cardiac defect. Conclusion: Our case shows that severe hypocalcemia can be the only presenting symptom in DiGeorge syndrome. Based on this case, we recommend physicians test for calcium levels and PTH at the first encounter with a patient who screened positive during NBS for SCID. Statement of Novelty: We describe an infant with DiGeorge syndrome who presented with severe hypocalcemia.

Background: Cytotoxic T lymphocyte-associated antigen-4 (CTLA4) haploinsufficiency is characterized by a variety of phenotypes, ranging from autoimmune disorders, enteropathy, fatal combined immunodeficiency, as well as lymphoproliferation and malignancy. Aim: To broaden the genotypic spectrum and clinical presentations of patients with CTLA4 variants. Methods: We evaluated a female patient with autoimmunity and lymphopenia. Immune workup and whole exome sequencing (WES) were performed. Results: The proband presented at 11 years of age with hypothyroidism and later developed Evans syndrome, alopecia, eczema, and lymphocytic interstitial pneumonia. Immune evaluation revealed T, B, and NK lymphopenia with normal humoral immunity. Following a negative genetic panel for autoimmune lymphoproliferative syndrome (ALPS), WES analysis identified a novel heterozygous intronic variant predicted in-silico to cause skipping of exon 2 of the CTLA4 gene. Conclusion: A novel heterozygous mutation in CTLA4 caused variable presentations of immune dysregulation, one of the hallmarks of CTLA4 haploinsufficiency. Statement of Novelty: We herein report a novel mutation in CTLA4 resulting in various features of autoimmunity.

Background: The T cell receptor (TCR)-α chain plays a key role in TCR structure and function. Biallelic mutations in TRAC, encoding the constant region of the TCR-α chain, obliterates TCR expression and results in immunodeficiency. TCR-α chain deficiency presents at infancy or childhood with repeated viral and bacterial infections, enlarged liver, spleen, and lymph nodes as well as autoimmune features and lymphoma (OMIM #615387). Aim: To broaden the genotypic and phenotypic spectrum of TCR-α chain deficiency. Methods: We present a case report of a patient with severe combined immunodeficiency (SCID) due to a novel autosomal recessive mutation in TRAC. Results: Our patient was identified at 13 days of life due to abnormal T cell receptor excision circle levels detected by newborn screening (NBS). Immune evaluation revealed profound lymphopenia, depressed responses to the mitogen PHA and a skewed T cell repertoire, all consistent with SCID. The patient was found to carry a novel homozygous mutation in the TRAC gene. Conclusion: A novel homozygous mutation in the TRAC gene caused profound T cell lymphopenia and aberrant in vitro mitogenic response, the hallmarks of SCID. Statement of Novelty: TCR-α chain deficiency is a rare and relatively new condition and not very well defined. We herein report a novel mutation in TRAC resulting in SCID.

In more than one-third of primary immunodeficiency (PID) patients, extensive genetic analysis including whole-exome sequencing (WES) fails to identify the genetic defect. Whole-genome sequencing (WGS) is able to detect variants missed by other genomics platforms, enabling the molecular diagnosis of otherwise unresolved cases. Here, we report two siblings, offspring of consanguineous parents, who experienced similar severe events encompassing early onset of colitis, lymphoproliferation, and hypogammaglobulinemia, typical of lipopolysaccharide-responsive and beige-like anchor (LRBA) or cytotoxic T lymphocyte antigen 4 (CTLA4) deficiencies. Gene-panel sequencing, comparative genomic hybridization (CGH) array, and WES failed to reveal a genetic aberration in relevant genes. WGS of these patients detected a 12.3 kb homozygous tandem duplication that was absent in control cohorts and is predicted to disrupt the reading frame of the LRBA gene. The variant was validated by PCR and Sanger sequencing, demonstrating the presence of the junction between the reference and the tandem-duplicated sequence. Droplet digital PCR (ddPCR) further confirmed the copy number in the unaffected parents (CN = 3, heterozygous) and affected siblings (CN = 4, homozygous), confirming the expected segregation pattern. In cases of suspected inherited immunodeficiency, WGS may reveal a mutation when other methods such as microarray and WES analysis failed to detect an aberration.

Background: The Forkhead box protein N1 (FOXN1) is a key regulator of thymic epithelial development, and its complete deficiency leads to a nude-severe combined immunodeficiency (SCID) phenotype. More recently, heterozygous mutations in FOXN1 have been linked with a syndrome of congenital lymphopenia and a wide clinical spectrum, with most cases being caused by missense mutations. Aim: To broaden the genotypic and phenotypic spectrum of heterozygous FOXN1 deficiency. Methods: Case report of a patient with FOXN1 haploinsufficiency due to a novel splice-site mutation. Results: Our patient was identified at 3 weeks of life given an abnormal newborn screen (NBS) for SCID, and was found to have congenital lymphopenia preferentially affecting CD8+ T-cells. Her cellular and humoral function were both excellent, and she has remained entirely asymptomatic and thriving for the first 3 years of her life. The patient was found on whole exome sequencing to carry a heterozygous splice-site mutation in the FOXN1 gene, affecting the Forkhead domain. The mutation was also identified in her asymptomatic mother. Conclusion: Heterozygous FOXN1 mutations are an increasingly-recognized cause of congenital lymphopenia. Our experience suggests most patients remain clinically well, with main manifestation including T-lymphopenia, mostly affecting CD8+ cells. Identification of the same variant in an asymptomatic parent suggests age-dependent improvement in T-cell counts and an overall benign course, while provides impetus for diligent conservative management with regular follow-up. Statement of novelty: Heterozygous FOXN1 deficiency is a relatively new entity, attributed in most cases to missense mutations in FOXN1. To further expand the knowledge basis regarding this emerging disorder, as well as its genotypic repertoire, we herein report a case of heterozygous FOXN1 deficiency caused by a splice site mutation.

BACKGROUND STAT1 gain-of-function (GOF) is an immune dysregulatory disorder with poorly studied genotype-phenotype correlation, impeding prognostication and early intervention. Given previous mechanistic studies, as well as anecdotal clinical reports, we sought to systematically determine whether DNA-binding domain (DBD) mutations in STAT1 result in a different phenotype than mutations in other gene domains. METHODS Negative prognostic features previously identified by the International STAT1 GOF Study Group (invasive infections, intracranial aneurysms, and malignancy), as well as other clinical features and mortality, were compared within a cohort of 30 patients with STAT1 GOF diagnosed at our center, consisting of 9 patients with DBD mutations and 21 patients with non-DBD mutations. We subsequently re-analyzed mortality data from a large, previously-published 274-patient cohort by the International STAT1 GOF Study Group. RESULTS While no differences were noted with respect to malignancy or symptomatic aneurysms, invasive /opportunistic infections were substantially more common among DBD patients, as were sinopulmonary infections, bronchiectasis, enteropathy, endocrinopathies, lymphoproliferative manifestations, and recurrent fevers/HLH. DBD patients also had a lower probability of survival and younger age of mortality compared with non-DBD patients. Our re-evaluation of the published data from the International STAT1 GOF Study Group revealed a similar finding of earlier mortality among patients harboring DBD mutations. CONCLUSION We report that STAT1 GOF patients with DBD mutations may be regarded as a unique subgroup, impacted more by early-onset profound combined immunodeficiency and with earlier mortality. These findings may impact clinical decision making with respect to early intervention, and in particular hematopoietic stem cell transplant considerations, in such patients.