Heterozygous FOXN1 Variants Cause Low TRECs and Severe T Cell Lymphopenia, Revealing a Crucial Role of FOXN1 in Supporting Early Thymopoiesis.

FOXN1 is the master regulatory gene of thymic epithelium development. FOXN1 deficiency leads to thymic aplasia, alopecia, and nail dystrophy, accounting for the nude/severe combined immunodeficiency (nu/SCID) phenotype in humans and mice. We identified several newborns with low levels of T cell receptor excision circles (TRECs) and T cell lymphopenia at birth, who carried heterozygous loss-of-function FOXN1 variants. Longitudinal analysis showed persistent T cell lymphopenia during infancy, often associated with nail dystrophy. Adult individuals with heterozygous FOXN1 variants had in most cases normal CD4+ but lower than normal CD8+ cell counts. We hypothesized a FOXN1 gene dosage effect on the function of thymic epithelial cells (TECs) and thymopoiesis and postulated that these effects would be more prominent early in life. To test this hypothesis, we analyzed TEC subset frequency and phenotype, early thymic progenitor (ETP) cell count, and expression of FOXN1 target genes (Ccl25, Cxcl12, Dll4, Scf, Psmb11, Prss16, and Cd83) in Foxn1nu/+ (nu/+) mice and age-matched wild-type (+/+) littermate controls. Both the frequency and the absolute count of ETP were significantly reduced in nu/+ mice up to 3 weeks of age. Analysis of the TEC compartment showed reduced expression of FOXN1 target genes and delayed maturation of the medullary TEC compartment in nu/+ mice. These observations establish a FOXN1 gene dosage effect on thymic function and identify FOXN1 haploinsufficiency as an important genetic determinant of T cell lymphopenia at birth.

Long-term outcome of LRBA deficiency in 76 patients after various treatment modalities as evaluated by the immune deficiency and dysregulation activity (IDDA) score.

BACKGROUND: Recent findings strongly support hematopoietic stem cell transplantation (HSCT) in patients with severe presentation of LPS-responsive beige-like anchor protein (LRBA) deficiency, but long-term follow-up and survival data beyond previous patient reports or meta-reviews are scarce for those patients who do not receive a transplant. OBJECTIVE: This international retrospective study was conducted to elucidate the longitudinal clinical course of patients with LRBA deficiency who do and do not receive a transplant. METHOD: We assessed disease burden and treatment responses with a specially developed immune deficiency and dysregulation activity score, reflecting the sum and severity of organ involvement and infections, days of hospitalization, supportive care requirements, and performance indices. RESULTS: Of 76 patients with LRBA deficiency from 29 centers (median follow-up, 10 years; range, 1-52), 24 underwent HSCT from 2005 to 2019. The overall survival rate after HSCT (median follow-up, 20 months) was 70.8% (17 of 24 patients); all deaths were due to nonspecific, early, transplant-related mortality. Currently, 82.7% of patients who did not receive a transplant (43 of 52; age range, 3-69 years) are alive. Of 17 HSCT survivors, 7 are in complete remission and 5 are in good partial remission without treatment (together, 12 of 17 [70.6%]). In contrast, only 5 of 43 patients who did not receive a transplant (11.6%) are without immunosuppression. Immune deficiency and dysregulation activity scores were significantly lower in patients who survived HSCT than in those receiving conventional treatment (P = .005) or in patients who received abatacept or sirolimus as compared with other therapies, and in patients with residual LRBA expression. Higher disease burden, longer duration before HSCT, and lung involvement were associated with poor outcome. CONCLUSION: The lifelong disease activity, implying a need for immunosuppression and risk of malignancy, must be weighed against the risks of HSCT.

Classification of asthma.

Asthma is a chronic inflammatory disorder of the airways that results, physiologically, in hyperreactivity and, clinically, in recurrent episodes of wheezing, chest tightness, or coughing. Airway inflammation, smooth-muscle contraction, epithelial sloughing, mucous hypersecretion, bronchial hyperresponsiveness, and mucosal edema contribute to the underlying pathophysiology of asthma. Diagnostic tests such as methacholine or mannitol challenges or spirometry (pre- and postbronchodilator responses) help to identify such underlying pathophysiology via assessments of bronchial hyperreactivity and lung mechanics but are imperfect and, ultimately, must be viewed in the context of a patient's clinical presentation, including response to pharmacotherapy. Asthma can be classified into either intermittent or persistent, and the latter is either mild, moderate, or severe. Some patients change, in either direction, from intermittent to persistent asthma. In addition, patients with asthma may be classified as allergic (immunoglobulin E mediated), nonallergic (often triggered by viral upper respiratory tract infections or no apparent cause), occupational, aspirin-exacerbated respiratory disease, potentially fatal, exercise-induced, and cough variant asthma. In the latter, the patients have a nonproductive cough that responds to treatment for asthma but not with antibiotics, expectorants, mucolytics, antitussives, or beta2-adrenergic agonists, and to treatment for acid reflux and rhinosinusitis. Thus, cough variant asthma is in the differential diagnosis of chronic cough.

The infant and toddler with wheezing.

Recurrent wheezing is common in young infants and toddlers, with 50% of all children having at least one wheezing episode in the first 6 years of life. Initial wheezing episodes in young children often are linked to respiratory infections due to viral pathogens, such as respiratory syncytial virus, human rhinovirus, human metapneumovirus, and influenza virus. Bacterial colonization of the neonatal airway also may be significant in the late development of recurrent wheeze and asthma. Wheezing in young children can be classified into specific phenotypes based on the onset and persistence of wheezing. Although some children will only wheeze transiently in early childhood, persistent wheezing is often classified as immunoglobulin E (IgE) associated and/or atopic or nonatopic. By using a modified asthma predictive index, future development of asthma can be interpreted, especially in high-risk populations. It is recommended to follow National Asthma Education and Prevention Program (NAEPP) guidelines for initiation of treatment; however, asthma management of young children often requires tailored regimens. Inhaled corticosteroids used as a daily controller medication have been shown to aid symptoms and exacerbation control; however, these do not change the natural course of the disease or progression to asthma. Although randomized double-blind studies in preschoolers investigated a role of macrolide antibiotics in early infection as well as high-dose inhaled corticosteroids during severe lower respiratory tract infections, more research is needed in this field to understand mechanisms of asthma development and optimal treatment in this young age group.

A 2-Year-Old Child with Alazami Syndrome with Newly Reported Findings of Immune Deficiency, Periventricular Nodular Heterotopia, and Stroke; Broadening the Phenotype of Alazami.

Alazami syndrome is a rare autosomal recessive neurodevelopmental disorder due to loss-of-function variants in the La ribonucleoprotein 7 (LARP7) gene. Children with Alazami syndrome are most often affected by a combination of primordial dwarfism, intellectual disability, and distinctive facial features. Previous cases have been primarily found in consanguineous families from the Middle East, Asia, and North Africa. We present a 21-month-old Caucasian male from the Midwest United States with nonconsanguineous parents who presented with frequently reported findings of unusual facial features, poor growth, cardiac and genitourinary findings, and developmental delay; less-frequently reported findings, including transient erythroblastopenia of childhood (TEC) and immune deficiency; and never-before reported findings of periventricular nodular heterotopia and stroke. He developed stroke during a hospitalization for Hemophilus influenzae meningitis. The possible contributions of LARP7 to TEC, immune deficiency, brain malformation, and stroke are discussed. Guidelines for the care of Alazami patients are proposed.

Lysophosphatidic acid stimulates epidermal growth factor-family ectodomain shedding and paracrine signaling from human lung fibroblasts.

Lysophospatidic acid (LPA) is a bioactive lipid mediator implicated in tissue repair and wound healing. It mediates diverse functional effects in fibroblasts, including proliferation, migration and contraction, but less is known about its ability to evoke paracrine signaling to other cell types involved in wound healing. We hypothesized that human pulmonary fibroblasts stimulated by LPA would exhibit ectodomain shedding of epidermal growth factor receptor (EGFR) ligands that signal to lung epithelial cells. To test this hypothesis, we used alkaline phosphatase-tagged EGFR ligand plasmids transfected into lung fibroblasts, and enzyme-linked immunosorbent assays to detect shedding of native ligands. LPA induced shedding of alkaline phosphatase-tagged heparin-binding epidermal growth factor (HB-EGF), amphiregulin, and transforming growth factor-a; non-transfected fibroblasts shed amphiregulin and HBEGF under baseline conditions, and increased shedding of HB-EGF in response to LPA. Treatment of fibroblasts with LPA resulted in elevated phosphorylation of extracellular signal-regulated kinase 1/2, enhanced expression of mRNA for c-fos, HB-EGF and amphiregulin, and enhanced proliferation at 96 hours. However, none of these fibroblast responses to LPA required ectodomain shedding or EGFR activity. To test the ability of LPA to stimulate paracrine signaling from fibroblasts, we transferred conditioned medium from LPA-stimulated cells, and found enhanced EGFR and extracellular signal-regulated kinase 1/2 phosphorylation in reporter A549 cells in excess of what could be accounted for by transferred LPA alone. These data show that LPA mediates EGF-family ectodomain shedding, resulting in enhanced paracrine signaling from lung fibroblasts to epithelial cells.

Dysregulated specific IgE production to bystander foods in children with peanut allergy but not egg allergy.

Background: Food specific immunoglobulin E (sIgE) levels are associated with the development of allergic responses and are used in the clinical evaluation of food allergy. Food sIgG4 levels have been associated with tolerance or clinical nonresponsiveness, particularly in interventional studies. Objective: We aimed to characterize food-specific antibody responses and compare responses with different foods in food allergy. Methods: Serum sIgA, sIgG4, and sIgE to whole peanut, egg white, and wheat, along with total IgE were measured in 57 children. Children with food allergy, children with natural tolerance, and controls were studied. The Mann-Whitney test or Kruskall Wallis test with the Dunn correction were used for statistical analysis. Results: As expected, total IgE levels were highest in the subjects with food allergy compared with the subjects who were nonallergic (p < 0.001) or the subjects who were naturally tolerant (p < 0.001). Peanut sIgE levels were higher in subjects with peanut allergy compared with the subjects who were naturally tolerant (p < 0.0001) and the control subjects (p < 0.03). Interestingly, peanut sIgG4 levels were also highest in children with peanut allergy compared with subjects who were naturally tolerant and control subjects (p = 0.28 and p < 0.001, respectively). Subjects with peanut allergy alone had comparable egg white sIgE levels to children with egg white allergy. In addition, the subjects with peanut allergy alone also had higher levels of egg white and wheat sIgE compared with the control subjects (p < 0.02 and p = 0.001, respectively). In contrast, the subjects with egg white allergy did not demonstrate elevated peanut or wheat sIgE levels. Conclusion: These novel findings suggested that IgE production is dysregulated in patients with peanut allergy, who are much less likely to outgrow their allergy, and suggest that the mechanisms that drive more persistent forms of food allergy may be distinct from more transient forms of food allergy.