We identified the genotype using a commercial lab (n = 92, 38.5%), the NGC in Oman (n = 20, 8.4%), and through external expert research BGLAP laboratories (n = 8, 3.3%). retrospectively report the epidemiological, clinical, immunological, and molecular findings and outcomes from 239 patients with IEI who were diagnosed and managed at the Royal Hospital, Oman, from January 2010 to October 2021. Results The estimated annual cumulative mean incidence of IEI was 25.5 per 100,000 Omani live births with a total prevalence of 15.5 per 100,000 Omani population. Both the high incidence and prevalence are attributed to the high rate of consanguinity (78.2%). Defects affecting cellular and humoral immunity including severe combined immunodeficiency (SCID), combined immunodeficiency (CID), and CID with syndromic features were the predominant defects in IEI (36%). Immune dysregulation was MX-69 a prominent manifestation and occurred in approximately a third of all patients with IEI (32%), with a mean age of onset of 81 months and a mean diagnostic delay of 50.8 months. The largest percentage of patients who showed such clinical signs were in the category of diseases of immune dysregulation (41%), followed by predominantly antibody deficiency (18%). The overall mortality rate MX-69 in our cohort was 25.1%, with higher death rates seen in CID including SCID and diseases of immune dysregulation. Conclusion Immune dysregulation is a frequent manifestation of Omani patients with IEI. Early detection through raising awareness of signs of IEI including those of immune dysregulation and implementation of newborn screening programs will result in early intervention and improved overall MX-69 outcome. Excel and GraphPad Prism-9 (GraphPad Software, Inc., San Diego, CA, USA). The results are expressed as means and medians with ranges and frequency (%) for continuous and categorical variables, respectively. The study was approved by the Research and Ethics Review and Approval Committee in the Ministry of Health, Sultanate of Oman. Patients We performed an analysis of a cohort of 239 children and adults with IEI, MX-69 who were seen and managed at the Royal Hospitalthe main governmental tertiary hospital in Omanfrom January 2010 to October 2021. The epidemiological details included the annual incidence per Omani live birth and the prevalence among the Omani population. The cumulative incidence MX-69 was calculated by defining the mean of the yearly new diagnoses of IEI from the annual population of Omani live births obtained from local registries for the last 11 years. Given that most of our cohort were from the pediatric age group, the Omani live birth group was considered a reasonable population at risk to extrapolate a relatively true incidence. However, prevalence included all patients with IEI who were diagnosed from the Omani population over the last 11 years. Additionally, other information such as demographics (sex and age), family history, and clinical manifestations of infection, immune dysregulation, and malignancy, as well as molecular diagnosis, long-term events, and outcomes were collected into an electronic database. The adopted diagnostic criteria were based on The European Society for Immunodeficiencies (ESID) Registry Working Definitions for the Clinical Diagnosis of IEI (14). The classification and subclassification of IEI were based on the Human Inborn Errors of Immunity: 2019 Update of the International Union of Immunological Societies (IUIS) Phenotypical Classification (1, 2). Age Categories and International Union of Immunological Societies (IUIS) Classification The age of onset and age of diagnosis were grouped into the following eight categories: 0C2, 3C5, 6C10, 11C15, 16C20, 21C30, 31C40, and 40 years. The phenotypic and genotypic classification was based on the main categories of IEI described in the IUIS (1, 2). Autoinflammatory disorders and syndromes of familial hemophagocytic lymphohistocytosis were excluded from the analysis due to the unavailability of patients details. Unclassified IEI was defined when the clinical phenotype and genotype did not fit the.