Very early-onset inflammatory bowel disease (VEO-IBD), defined as IBD diagnosed before 6 years of age, is highly influenced by genetic factors. Monogenic IBD is a type of enterocolitis caused by a single pathogenic variant. However, information on Asian patients with VEO-IBD and monogenic IBD is limited. This study investigated real-world data on VEOIBD and monogenic IBD in Japan. We evaluated patients with VEO-IBD registered in the Japanese Pediatric Inflammatory Bowel Disease Registry, a multicenter prospective registry study conducted between 2012 and 2021. We categorized patients into monogenic and non-monogenic IBD groups and compared their clinical characteristics and outcomes. Among 703 pediatric patients with IBD, 68 (9.7%) had VEO-IBD. Of these, 26 (38.2%) had ulcerative colitis, 16 (23.5%) had Crohn's disease, 23 (33.8%) had unclassified IBD (IBD-U), and 3 (4.4%) had Behçet's disease. Genetic testing was performed in 25 patients (36.8%), and monogenic IBD was identified in 5 of the 23 patients with IBD-U (7.4% of the VEO-IBD cohort). All 5 monogenic cases presented with an IBD-U phenotype. Monogenic IBD included A20 haploinsufficiency, interleukin-10 receptor subunit alpha deficiency, chronic granulomatous disease, Wiskott-Aldrich syndrome, and Hermansky-Pudlak syndrome. Monogenic IBD was significantly associated with IBD-U phenotype (P= 0.015) and severe infections before 1 year of age (P= 0.004). Patients with VEO-IBD who present an IBD-U phenotype and have a history of severe infections during infancy should be prioritized for genetic analysis to investigate the possibility of monogenic IBD.

Hermansky-Pudlak Syndrome (HPS) type 1 (HPS-1) is an autosomal recessive disorder characterized by oculocutaneous albinism, platelet dysfunction, and pulmonary fibrosis (HPS-PF), the leading cause of mortality in these patients. HPS-PF manifests earlier than idiopathic pulmonary fibrosis, typically between 30 and 40 years of age. The etiology and drivers of HPS-PF progression remain poorly understood, and no FDA-approved therapies exist. Neutrophil extracellular traps (NETs) and neutrophil-derived mediators have emerged as key players in fibrosis, promoting lung injury, inflammation, and fibroblast activation. This study evaluates the role of neutrophil activation in age-related changes in patients with HPS-1, focusing on differences in inflammatory markers, neutrophil granules, and NETosis capacity. We observed significantly elevated levels of NETs, neutrophil granule proteins (NE, NGAL, LF), and inflammatory cytokines (IL-8, IL-6) in patients with HPS-1 older than 40 years compared to younger patients and healthy controls. Additionally, fibrosis-related markers (MMP-7 and MMP-8) were significantly higher in older patients. Elevated levels of anandamide (AEA), a circulating marker of HPS-PF, were positively associated with neutrophil granule markers in older patients, suggesting its association with fibrosis. Neutrophils from older patients also demonstrated increased NETosis capacity. These findings suggest that age-related neutrophil activation may contribute to an inflammatory environment that promotes fibrosis progression in HPS-1.

The longitudinal cellular interactions that drive pulmonary fibrosis are not well understood. To investigate the disease underpinnings associated with fibrosis onset and progression, we generated a scRNA-seq atlas of lungs from young and aged mouse models of multiple subtypes of Hermansky-Pudlak syndrome (HPS), a collection of rare autosomal recessive diseases associated with albinism, platelet dysfunction, and pulmonary fibrosis. We have identified an age-dependent increase in SAA3+ inflammatory lung fibroblasts in HPS mice, including in double-mutant HPS1-2 mice which develop spontaneous fibrosis. HPS1 fibroblasts show increased expression of IL-1R1, whereas alveolar type II epithelial cells from HPS2 mice induce the inflammatory gene signature in co-cultured fibroblasts. scRNA-seq of lung tissue from three HPS1 patients similarly shows the presence of inflammatory fibroblasts and increased IL1R1 expression on fibroblasts. These data posit complex interactions between dysfunctional epithelial cells, inflammatory fibroblasts, and recruited immune cells, suggesting potential opportunities for mitigation of the fibrotic cascade.

Congenital neutropenia (CoN) is a heterogeneous group of inborn errors of immunity (IEI) characterized by recurrent infections and early onset of neutropenia (NP). This study aimed to investigate the demographic and clinical data of children with CoN and idiopathic neutropenia (IN) in Morocco. We performed a retrospective study of patients with CoN and analyzed the clinical and laboratory findings of patients with CoN and IN diagnosed between 1999 and 2018 in a clinical immunology unit of a large pediatric hospital. We identified 88 patients, 51 with IN and 37 with CoN. Fifty-seven percent were males, and 43% were females, ranging from 1 month to 19 years. The median age at onset was 8 months, and the median at diagnosis was 36 months. Consanguinity was observed in 57% of the cases, and a history of recurrent infections in the siblings was found in 27.3%. The most common infectious complications were ear, nose, and throat (ENT) infections, skin and soft tissue infections, and lung infections. Patients with CoN were classified into seven syndromes: 9 with severe congenital neutropenia, 11 with cyclic neutropenia, 6 with glycogen storage disease type 1b, 5 with poikiloderma with neutropenia, 3 with Griscelli syndrome, 2 with Hermansky-Pudlak syndrome type II, and 1 with Cohen syndrome. This study provides a comprehensive overview of CoN and IN in a pediatric cohort from Morocco, representing the country's most considerable single-center investigation of these conditions. Our findings highlight the significant burden of CoN, accounting for 5% of IEI in the Moroccan registry, a proportion higher than in some neighboring countries. The study emphasizes the early onset and severity of bacterial infections in CoN patients, underlining the critical need for timely and accurate diagnosis.

Hermansky-Pudlak syndrome (HPS) is a genetic disorder of endosomal protein trafficking associated with pulmonary fibrosis in specific subtypes, including HPS-1 and HPS-2. Single-mutant HPS1 and HPS2 mice display increased fibrotic sensitivity while double-mutant HPS1/2 mice exhibit spontaneous fibrosis with aging, which has been attributed to HPS mutations in alveolar epithelial type II (AT2) cells. We utilized HPS mouse models and human lung tissue to investigate mechanisms of AT2 cell dysfunction driving fibrotic remodeling in HPS. Starting at 8 weeks of age, HPS mice exhibited progressive loss of AT2 cell numbers. HPS AT2 cell function was impaired ex vivo and in vivo. Incorporating AT2 cell lineage tracing in HPS mice, we observed aberrant differentiation with increased AT2-derived alveolar epithelial type I cells. Transcriptomic analysis of HPS AT2 cells revealed elevated expression of genes associated with aberrant differentiation and p53 activation. Lineage-tracing and organoid-modeling studies demonstrated that HPS AT2 cells were primed to persist in a Keratin-8-positive reprogrammed transitional state, mediated by p53 activity. Intrinsic AT2 progenitor cell dysfunction and p53 pathway dysregulation are mechanisms of disease in HPS-related pulmonary fibrosis, with the potential for early targeted intervention before the onset of fibrotic lung disease.