Non-Skewed X-inactivation Results in NF-κB Essential Modulator (NEMO) Δ-exon 5-autoinflammatory Syndrome (NEMO-NDAS) in a Female with Incontinentia Pigmenti

Purpose: Genetic hypomorphic defects in X chromosomal IKBKG coding for the NF-κB essential modulator (NEMO) lead to ectodermal dysplasia and immunodeficiency in males and the skin disorder incontinentia pigmenti (IP) in females, respectively. NF-κB essential modulator (NEMO) Δ-exon 5-autoinflammatory syndrome (NEMO-NDAS) is a systemic autoinflammatory disease caused by alternative splicing and increased proportion of NEMO-Δex5. We investigated a female carrier presenting with IP and NEMO-NDAS due to non-skewed X-inactivation.

Methods: IKBKG transcripts were quantified in peripheral blood mononuclear cells isolated from the patient, her mother, and healthy controls using RT-PCR and nanopore sequencing. Corresponding proteins were analyzed by western blotting and flow cytometry. Besides toll-like receptor (TLR) and tumor necrosis factor (TNF) signaling, the interferon signature, cytokine production and X-inactivation status were investigated.

Results: IP and autoinflammation with recurrent fever, oral ulcers, hepatitis, and neutropenia, but no immunodeficiency was observed in a female patient. Besides moderately reduced NEMO signaling function, type I interferonopathy, and elevated IL-18 and CXCL10 were found. She and her mother both carried the heterozygous variant c.613 C > T p.(Gln205*) in exon 5 of IKBKG previously reported in NEMO-deficient patients. However, X-inactivation was skewed in the mother, but not in the patient. Alternative splicing led to increased ratios of NEMO-Dex5 over full-length protein in peripheral blood cell subsets causing autoinflammation. Clinical symptoms partially resolved under treatment with TNF inhibitors.

Conclusion: Non-skewed X-inactivation can lead to NEMO-NDAS in females with IP carrying hypomorphic IKBKG variants due to alternative splicing and increased proportions of NEMO-∆ex5.