Clinical and immunological characterization of a child with a homozygous TBK1 kinase-domain truncation.

TBK1 is a serine-tyrosine kinase protein that transmits signals from pattern recognition receptors to the NF-κB pathway leading to production of Type 1 Interferons. Mutations in this protein have been associated with arthritis, vasculitis, herpes simplex encephalitis and amyotrophic lateral sclerosis. In the current study, we characterized the functional consequences of a TBK1-variant bearing a truncation in exon 4 and 5 in a patient with poly arthritis resembling juvenile idiopathic arthritis and necrotizing encephalitis. The truncation was associated with reduced TBK1 protein abundance and altered phosphorylation. The variant was associated with increased basal/and or Poly-I: C induced IL-6, TNFα, IL-1β and IL-18 and type 1 Interferon ex vivo. Our findings expand the phenotypic spectrum of TBK1 loss-of-function variants and may provide insight into the management of immune dysregulation in affected patients.