Atypical Hemolytic Uremic Syndrome (aHUS) and Adenosine Deaminase (ADA)-Deficient Severe Combined Immunodeficiency (SCID)-Two Diseases That Exacerbate Each Other: Case Report.

Hemolytic uremic syndrome (HUS) is defined by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury (AKI). Atypical HUS (aHUS), distinguished by its etiology, is caused by uncontrolled overactivation of the alternative complement pathway. The correct diagnosis of aHUS is complex and involves various gene mutations. Severe combined immunodeficiency (SCID), characterized by severe T-cell lymphocytopenia and a lack of antigen-specific T-cell and B-cell immune responses, is of seldom occurrence. In 10-15% of pediatric patients, SCID is caused by adenosine deaminase (ADA) deficiency. The authors describe the case of a boy who suffered from both aHUS and ADA-deficient SCID. At the age of 9 months, the patient presented acute kidney injury with anuria and coagulopathy. The diagnosis of aHUS was established on the basis of alternative complement pathway deregulation and disease-associated gene mutations. Further examination revealed immune system failure and, at the age of 13 months, the ADA deficiency was confirmed by genetic tests and the boy was diagnosed with ADA-SCID. ADA SCID has recently been described as a possible triggering factor of aHUS development and progression. However, more research is required in this field. Nevertheless, it is crucial in clinical practice to be aware of these two co-existing life-threatening diseases.

Deficiency of Adenosine Deaminase 2 in Adults and Children: Experience From India.

OBJECTIVE: Deficiency of adenosine deaminase 2 (DADA2) is a potentially fatal monogenic syndrome characterized by variable manifestations of systemic vasculitis, bone marrow failure, and immunodeficiency. Most cases are diagnosed by pediatric care providers, given the typical early age of disease onset. This study was undertaken to describe the clinical phenotypes and treatment response both in adults and in children with DADA2 in India. METHODS: A retrospective analysis of pediatric and adult patients with DADA2 diagnosed at various rheumatology centers across India was conducted. Clinical characteristics, diagnostic findings, and treatment responses were analyzed in all subjects. RESULTS: In total, 33 cases of DADA2 were confirmed in this cohort between April 2017 and March 2020. Unlike previous studies, nearly one-half of the confirmed cases presented during adulthood. All symptomatic patients exhibited features of vasculitis, whereas constitutional symptoms and anemia were more common in pediatric patients. Cutaneous and neurologic involvement were common, and 18 subjects had experienced at least one stroke. In addition, the clinical spectrum of DADA2 was expanded by recognition of novel features in these patients, including pancreatic infarction, focal myocarditis, and diffuse alveolar hemorrhage. Treatment with tumor necrosis factor inhibitors (TNFi) was initiated in 25 patients. All of the identified disease manifestations showed marked improvement after initiation of TNFi, and disease remission was achieved in 19 patients. Two cases were complicated by tuberculosis infection, and 2 deaths were reported. CONCLUSION: This report presents the first case series of patients with DADA2 from India, diagnosed by adult and pediatric care providers. The findings raise awareness of this syndrome, particularly with regard to its presentation in adults.

Urogenital Abnormalities in Adenosine Deaminase Deficiency.

BACKGROUND: Improved survival in ADA-SCID patients is revealing new aspects of the systemic disorder. Although increasing numbers of reports describe the systemic manifestations of adenosine deaminase deficiency, currently there are no studies in the literature evaluating genital development and pubertal progress in these patients. METHODS: We collected retrospective data on urogenital system and pubertal development of 86 ADA-SCID patients followed in the period 2000-2017 at the Great Ormond Street Hospital (UK) and 5 centers in Italy. In particular, we recorded clinical history and visits, and routine blood tests and ultrasound scans were performed as part of patients' follow-up. RESULTS AND DISCUSSION: We found a higher frequency of congenital and acquired undescended testes compared with healthy children (congenital, 22% in our sample, 0.5-4% described in healthy children; acquired, 16% in our sample, 1-3% in healthy children), mostly requiring orchidopexy. No urogenital abnormalities were noted in females. Spontaneous pubertal development occurred in the majority of female and male patients with a few cases of precocious or delayed puberty; no patient presented high FSH values. Neither ADA-SCID nor treatment performed (PEG-ADA, BMT, or GT) affected pubertal development or gonadic function. CONCLUSION: In summary, this report describes a high prevalence of cryptorchidism in a cohort of male ADA-SCID patients which could represent an additional systemic manifestation of ADA-SCID. Considering the impact urogenital and pubertal abnormalities can have on patients' quality of life, we feel it is essential to include urogenital evaluation in ADA-SCID patients to detect any abnormalities, initiate early treatment, and prevent long-term complications.

Survival of human cadaver skin on severe combined immune deficiency pigs: Proof of concept.

Transplantation of human xenografts onto immunocompromised mice is a powerful research tool for studying wound healing. However, differences in healing between humans and mice and their small size limit this model. We determined whether human cadaver skin xenografts transplanted onto pigs with severe combined immune deficiency (SCID) would survive and not be rejected. Meshed (1:1.5), cryopreserved human cadaver skin was transplanted onto 10 partial thickness dermatome wounds in each of two normal domestic pigs and two SCID pigs. Autografts (n = 2/animal) from the four animals were used as controls. In normal pigs, all autografts were engrafted and healed with a minimal, if any, inflammation and scarring. All human xenografts were rejected by the normal pigs within 5-11 days and associated with an intense T-cell inflammatory response. In contrast, both autografts and xenografts were engrafted and survived the 28-day study in the SCID pigs with a minimal inflammation and no gross scarring.

Reticular dysgenesis-associated AK2 protects hematopoietic stem and progenitor cell development from oxidative stress.

Adenylate kinases (AKs) are phosphotransferases that regulate the cellular adenine nucleotide composition and play a critical role in the energy homeostasis of all tissues. The AK2 isoenzyme is expressed in the mitochondrial intermembrane space and is mutated in reticular dysgenesis (RD), a rare form of severe combined immunodeficiency (SCID) in humans. RD is characterized by a maturation arrest in the myeloid and lymphoid lineages, leading to early onset, recurrent, and overwhelming infections. To gain insight into the pathophysiology of RD, we studied the effects of AK2 deficiency using the zebrafish model and induced pluripotent stem cells (iPSCs) derived from fibroblasts of an RD patient. In zebrafish, Ak2 deficiency affected hematopoietic stem and progenitor cell (HSPC) development with increased oxidative stress and apoptosis. AK2-deficient iPSCs recapitulated the characteristic myeloid maturation arrest at the promyelocyte stage and demonstrated an increased AMP/ADP ratio, indicative of an energy-depleted adenine nucleotide profile. Antioxidant treatment rescued the hematopoietic phenotypes in vivo in ak2 mutant zebrafish and restored differentiation of AK2-deficient iPSCs into mature granulocytes. Our results link hematopoietic cell fate in AK2 deficiency to cellular energy depletion and increased oxidative stress. This points to the potential use of antioxidants as a supportive therapeutic modality for patients with RD.

Inborn errors of the development of human natural killer cells.

PURPOSE OF REVIEW: Inborn errors of human natural killer (NK) cells may affect the development of these cells, their function, or both. There are two broad categories of genetic defects of NK cell development, depending on whether the deficiency is apparently specific to NK cells or clearly affects multiple hematopoietic lineages. We review here recent progress in the genetic dissection of these NK deficiencies (NKDs). RECENT FINDINGS: Patients with severe combined immunodeficiencies bearing mutations of adenosine deaminase, adenylate kinase 2, interleukin-2 receptor gamma chain, and Janus kinase 3 genes present NKDs and are prone to a broad range of infections. Patients with GATA binding protein 2 deficiency are susceptible to both mycobacterial and viral infections, and display NKDs and a lack of monocytes. Rare patients with mini chromosomal maintenance 4 deficiency display an apparently selective NKD associated with viral infections, but they also display various nonhematopoietic phenotypes, including adrenal insufficiency and growth retardation. SUMMARY: These studies have initiated a genetic dissection of the development of human NK cells. Further studies are warranted, including the search for genetic causes of NKD in particular. This research may lead to the discovery of molecules specifically controlling the development of NK cells and to improvements in our understanding of the hitherto elusive function of these cells in humans.

IL-22 and IDO1 affect immunity and tolerance to murine and human vaginal candidiasis.

The ability to tolerate Candida albicans, a human commensal of the gastrointestinal tract and vagina, implicates that host defense mechanisms of resistance and tolerance cooperate to limit fungal burden and inflammation at the different body sites. We evaluated resistance and tolerance to the fungus in experimental and human vulvovaginal candidiasis (VVC) as well as in recurrent VVC (RVVC). Resistance and tolerance mechanisms were both activated in murine VVC, involving IL-22 and IL-10-producing regulatory T cells, respectively, with a major contribution by the enzyme indoleamine 2,3-dioxygenase 1 (IDO1). IDO1 was responsible for the production of tolerogenic kynurenines, such that replacement therapy with kynurenines restored immunoprotection to VVC. In humans, two functional genetic variants in IL22 and IDO1 genes were found to be associated with heightened resistance to RVVC, and they correlated with increased local expression of IL-22, IDO1 and kynurenines. Thus, IL-22 and IDO1 are crucial in balancing resistance with tolerance to Candida, their deficiencies are risk factors for RVVC, and targeting tolerance via therapeutic kynurenines may benefit patients with RVVC.

Diseases associated with defective responses to DNA damage.

Within the last decade, multiple novel congenital human disorders have been described with genetic defects in known and/or novel components of several well-known DNA repair and damage response pathways. Examples include disorders of impaired nucleotide excision repair, DNA double-strand and single-strand break repair, as well as compromised DNA damage-induced signal transduction including phosphorylation and ubiquitination. These conditions further reinforce the importance of multiple genome stability pathways for health and development in humans. Furthermore, these conditions inform our knowledge of the biology of the mechanics of genome stability and in some cases provide potential routes to help exploit these pathways therapeutically. Here, I will review a selection of these exciting findings from the perspective of the disorders themselves, describing how they were identified, how genotype informs phenotype, and how these defects contribute to our growing understanding of genome stability pathways.

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 forms of 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.

The long quest for neonatal screening for severe combined immunodeficiency.

Early recognition of severe combined immunodeficiency (SCID) is a pediatric emergency because a diagnosis before live vaccines or nonirradiated blood products are given and before development of infections permits lifesaving unfractionated HLA-identical or T cell-depleted haploidentical hematopoietic stem cell transplantation, enzyme replacement therapy, or gene therapy. The need for newborn screening for this condition has been recognized for the past 15 years. However, implementation of screening required development of an assay for T-cell lymphopenia that could be performed on dried bloodspots routinely collected from newborn infants for the past 48 years. This was accomplished 6 years ago, and there have already been 7 successful pilot studies. A recommendation to add SCID to the routine newborn-screening panel was approved by the Secretary's Advisory Committee on Heritable Disorders of Newborns and Children in 2010 and was soon after approved by the Secretary of Health and Human Services. It is important for allergists, immunologists, and other health care providers to take an active role in promoting newborn screening for SCID and other T-lymphocyte abnormalities in their states. Even more important will be their roles in establishing accurate diagnoses for infants with positive screen results and in ensuring that they are given the best possible treatment.

CD27 deficiency is associated with combined immunodeficiency and persistent symptomatic EBV viremia.

BACKGROUND: CD27 is a lymphocyte costimulatory molecule that regulates T-cell, natural killer (NK) cell, B-cell, and plasma cell function, survival, and differentiation. On the basis of its function and expression pattern, we considered CD27 a candidate gene in patients with hypogammaglobulinemia. OBJECTIVE: We sought to describe the clinical and immunologic phenotypes of patients with genetic CD27 deficiency. METHODS: A molecular and extended immunologic analysis was performed on 2 patients lacking CD27 expression. RESULTS: We identified 2 brothers with a homozygous mutation in CD27 leading to absence of CD27 expression. Both patients had persistent symptomatic EBV viremia. The index patient was hypogammaglobulinemic, and immunoglobulin replacement therapy was initiated. His brother had aplastic anemia in the course of his EBV infection and died from fulminant gram-positive bacterial sepsis. Immunologically, lack of CD27 expression was associated with impaired T cell-dependent B-cell responses and T-cell dysfunction. CONCLUSION: Our findings identify a role for CD27 in human subjects and suggest that this deficiency can explain particular cases of persistent symptomatic EBV viremia with hypogammaglobulinemia and impaired T cell-dependent antibody generation.

Essential role for DNA-PK-mediated phosphorylation of NR4A nuclear orphan receptors in DNA double-strand break repair.

DNA-dependent protein kinase (DNA-PK) is a central regulator of DNA double-strand break (DSB) repair; however, the identity of relevant DNA-PK substrates has remained elusive. NR4A nuclear orphan receptors function as sequence-specific DNA-binding transcription factors that participate in adaptive and stress-related cell responses. We show here that NR4A proteins interact with the DNA-PK catalytic subunit and, upon exposure to DNA damage, translocate to DSB foci by a mechanism requiring the activity of poly(ADP-ribose) polymerase-1 (PARP-1). At DNA repair foci, NR4A is phosphorylated by DNA-PK and promotes DSB repair. Notably, NR4A transcriptional activity is entirely dispensable in this function, and core components of the DNA repair machinery are not transcriptionally regulated by NR4A. Instead, NR4A functions directly at DNA repair sites by a process that requires phosphorylation by DNA-PK. Furthermore, a severe combined immunodeficiency (SCID)-causing mutation in the human gene encoding the DNA-PK catalytic subunit impairs the interaction and phosphorylation of NR4A at DSBs. Thus, NR4As represent an entirely novel component of DNA damage response and are substrates of DNA-PK in the process of DSB repair.

Omenn syndrome does not live by V(D)J recombination alone.

PURPOSE OF REVIEW: During the past decade, easy access to sequence analyses has allowed us to increase our understanding of the pathogenesis of severe combined immunodeficiencies. Here, we describe the expanding clinical and immunological spectrum associated with Omenn syndrome phenotype. In particular, we review the cellular and molecular mechanisms involved in the pathophysiology of 'classical' Omenn syndrome due to the recombination activating gene (RAG) defects and of a new subgroup of Omenn-like disorders. RECENT FINDINGS: Different types of mutations are associated with the Omenn phenotype characterized by skin erythroderma, oligoclonal-activated T cells and elevated IgE in the absence of circulating B cells. Extensive studies conducted over the last few years have allowed the definition of the 'classical form' of Omenn syndrome due to hypomorphic defects in genes involved in V(D)J recombination, mainly RAG genes, and 'Omenn-like' features associated with mutations in genes involved in the maturation steps of lymphoid cells other than V(D)J recombination. Moreover, an increasing number of diseases other than those due to V(D)J recombination defects develop Omenn signs. SUMMARY: Impaired but not abolished V(D)J recombination process leads to the generation of a few T cells which expand in the periphery, infiltrate target organs such as skin and gut, resulting in severe erythroderma and colitis, both typical signs of Omenn syndrome. Extensive molecular studies now demonstrate that genes other than V(D)J molecules have a role in the pathogenesis of this disease, supporting the evidence that 'Omenn' defines an inflammatory condition associated with various genetic defects.

Clinical characteristics and molecular analysis of three Chinese children with Omenn syndrome.

Omenn syndrome (OS) is a rare autosomal recessive genetic disorder and presents symptoms of severe combined immunodeficiency characterized by erythrodermia, eosinophilia, hepatosplenomegaly, lymphadenopathy, and elevated serum IgE levels. OS has been found to be caused by mutations in RAG1 or RAG2 gene that result in partial V(D)J recombination activity. No study on OS has been reported in Chinese children so far. In this study, the genotype and phenotypes of three infants with OS from three unrelated Chinese families were investigated. All the three children had most of the characteristics of OS except normal serum IgE level. Compound heterozygosity mutations in RAG1 gene (1983 G>A; 2444 C>T and 2219 C>T; 3127 C>G) were identified in two cases, and a homozygous deletion mutation with a premature stop codon was found at residue 2302 of RAG1 gene (2302delT, I729X) in the remaining case, including three novel mutations (2302delT, I729X; 2219 C>T, R699W; and 3127 C>G, Y1001X). Spectratyping analysis of T-cell receptor ß-chain variable region (TCRVß) gene rearrangement was performed in case 1 and case 2. All the 25 TCRVß subfamilies presented monoclonal or oligoclonal peaks in case 1 and 11 TCRVß subfamilies were very weak or even absent in case 2. This was the first report about OS in Chinese children. Molecular genetic testing represents an important tool for early confirmed diagnosis and may allow accurate carrier detection and prenatal diagnosis.

Somatic mosaicism caused by monoallelic reversion of a mutation in T cells of a patient with ADA-SCID and the effects of enzyme replacement therapy on the revertant phenotype.

Patients with adenosine deaminase (ADA) deficiency exhibit spontaneous and partial clinical remission associated with somatic reversion of inherited mutations. We report a child with severe combined immunodeficiency (T-B- SCID) due to ADA deficiency diagnosed at the age of 1 month, whose lymphocyte counts including CD4+ and CD8+ T and NK cells began to improve after several months with normalization of ADA activity in Peripheral blood lymphocytes (PBL), as a result of somatic mosaicism caused by monoallelic reversion of the causative mutation in the ADA gene. He was not eligible for haematopoietic stem cell transplantation (HSCT) or gene therapy (GT); therefore he was placed on enzyme replacement therapy (ERT) with bovine PEG-ADA. The follow-up of metabolic and immunologic responses to ERT included gradual improvement in ADA activity in erythrocytes and transient expansion of most lymphocyte subsets, followed by gradual stabilization of CD4+ and CD8+ T (with naïve phenotype) and NK cells, and sustained expansion of TCRγδ+ T cells. This was accompanied by the disappearance of the revertant T cells as shown by DNA sequencing from PBL. Although the patient's clinical condition improved marginally, he later developed a germinal cell tumour and eventually died at the age of 67 months from sepsis. This case adds to our current knowledge of spontaneous reversion of mutations in ADA deficiency and shows that the effects of the ERT may vary among these patients, suggesting that it could depend on the cell and type in which the somatic mosaicism is established upon reversion.

Increased resting energy expenditure is associated with failure to thrive in infants with severe combined immunodeficiency.

OBJECTIVES: To measure resting energy expenditure (REE) and determine whether increased REE (hypermetabolism) is associated with failure to thrive (FTT) in patients with severe combined immunodeficiency (SCID) at diagnosis. STUDY DESIGN: REE was measured in 26 patients with SCID in a single transplant center. Predicted REE was determined with World Health Organization standards. Measured REE >110% of predicted REE was classified as hypermetabolism. Other data collected included FTT status, infections, genotype, phenotype, and the feeding methods used. RESULTS: Fifteen of 26 patients (57.7%) had FTT, and 18 of 26 patients (69.2%) were hypermetabolic. Hypermetabolism occured in 14 of 15 patients (93%) with FTT, and only 4 of 11 patients (36%) without FTT had hypermetabolism (P = .003). There was a significant difference between the measured REE (71.75 ± 16.6 kcal/kg) and the predicted REE (52.85 ± 2.8 kcal/kg; P < .0001). Eleven of 17 patients (65%) required nasogastric feeding, parenteral nutrition, or both to meet their energy needs. CONCLUSIONS: Hypermetabolism is common in patients with SCID and may contribute to the development of FTT. The hypermetabolism in these patients may necessitate intensive nutrition support.