- D1.338 - Divergent Clinical and Functional Consequences of Canonical NF-κB Pathway Defects

The canonical NF-κB pathway is a central regulator of innate and adaptive immunity. Upon pro-inflammatory stimulation, activation of the IKK complex (IKKα, IKKβ, and IKKγ/NEMO) leads to phosphorylation and degradation of IκBα, enabling NF-κB–dependent transcription of genes involved in inflammation and cell survival. Defects in this pathway underlie inborn errors of immunity with diverse phenotypes, ranging from immunodeficiency to immune dysregulation and malignancy. We describe a multicentre cohort of patients with canonical NF-κB signaling defects and functionally characterize the impact of known and novel variants.

The cohort included 7 patients with X-linked variants in IKBKG (NEMO), including one previously unreported variant; 2 patients with NFKBIA (IκBα) variants, including one novel variant; and 1 patient with novel variant in RELA (RelA). Peripheral blood leukocytes were analyzed using 12-color immunophenotyping. Cytokine production was assessed by flow cytometry and Luminex assays. NF-κB activation was evaluated using single-cell phospho-flow cytometry and western blotting for phosphorylated NF-κB p65 (Ser536) and IκBα, complemented by mRNA quantification of five NF-κB target genes. 

Patients with previously reported IKBKG loss-of-function (LOF) variants presented with infections, neutropenia or lymphopenia, reduced mature B cells, and hypogammaglobulinemia. In contrast, a patient with a novel IKBKG variant exhibited ectodermal dysplasia, infancy-onset fever with elevated inflammatory markers, thrombocytosis, neutrophilia, lymphocytosis, and hypergammaglobulinemia. One patient with NFKBIA variant developed inflammatory bowel disease, while another presented with ectodermal dysplasia, early-onset systemic inflammation, cutaneous papulopustulosis, multiorgan inflammatory disease, thrombocytosis, neutrophilia, and combined immunodeficiency. The patient with RELA variant developed Hodgkin lymphoma. Functionally, IKBKG LOF variants were associated with impaired NF-κB activation and reduced IL-1β, IL-6, and TNF-α production. In contrast, patients with novel IKBKG and NFKBIA variants showed increased production of IL-1β, IL-6, and IL-8, consistent with hyperinflammatory immune dysregulation and are being further investigated.

Canonical NF-κB pathway defects can result in either impaired or excessive immune activation. Detailed functional characterization of novel variants is essential for accurate diagnosis and optimized clinical management.