[Clinical features and functional validation of IRAK4 gene deficiency]

Objective: To characterize the clinical and genetic features of 2 patients with interleukin-1 receptor associated kinase (IRAK) 4 deficiency and to assess the pathogenicity of their genetic variants. Methods: This case series included two patients diagnosed with IRAK4 gene deficiency at Shenzhen Children's Hospital and the University of Hong Kong-Shenzhen Hospital between 2019 and 2024. Six healthy children without recent infections or immunodeficiency served as controls. Peripheral blood mononuclear cells were stimulated in vitro with Toll-like receptor 4 (TLR4) agonists, and cytokine levels were quantified using a protein chip assay. Results: The 2 patients, a 5-year-old boy and a 10-year-old girl, presented with recurrent invasive or non-invasive bacterial infections and impaired acute-phase inflammatory responses. Genetic testing identified a homozygous frameshift variant (c.540delT, p.F180Lfs*26) in Patient 1 and compound heterozygous frameshift variants (c.166delT, p.F56fs and c.629delG, p.R210fs) in Patient 2, all predicted to result in truncated IRAK4 proteins. Both patients received regular infection prophylaxis with favorable clinical outcomes. Controls consists of 3 males and 3 females, aged 5-17 years. Following TLR4 stimulation, cytokine levels in Patient 1, Patient 2, and controls (tumor necrosis factor-α 68.6, 103.0, 618.7 (392.7, 824.1); interleukin (IL)-1β 39.8, 10.8, 1 975.5 (1 556.0, 2 096.5); interferon-γ 8.6, 6.2, 13.5 (12.7, 14.9); granulocyte colony-stimulating factor 17.6, 15.9, 2 890.0 (1 622.0, 4 692.8); IL-6 140.1, 352.7, 7 222.5 (5 768.5, 8 043.5); and IL-17 47.5, 44.5, 59.7 (43.4, 69.5), respectively. Conclusions: IRAK4 deficiency should be suspected in patients with early-onset recurrent bacterial infections and attenuated inflammatory response. Homozygous and compound heterozygous frameshift variants in IRAK4 gene lead to truncated IRAK4 proteins and impared innate immune signaling.