Susceptibility of nucleotide-binding oligomerization domain 2 mutations to Whipple's disease

Objectives: Whipple's disease (WD) results from infection of the bacteria Tropheryma whipplei (TW). This disease is characterized by macrophage infiltration of intestinal mucosa and primarily affects Caucasian males. Genetic studies of host susceptibility are scarce. Nucleotide-binding oligomerization domain containing protein 2 (NOD2) is an innate immune sensor, resides mainly in monocytes/macrophages and contributes to defence against infection and inflammatory regulation. NOD2 mutations are associated with autoinflammatory diseases. We report the association of NOD2 mutations with TW and WD for the first time. Methods: A multicentre, retrospective study of three patients with WD was conducted. Patients received extensive multidisciplinary evaluations and were cared for by the authors. NOD2 and its association with infection and inflammation were schematically represented. Results: All patients were Caucasian men and presented with years of autoinflammatory phenotypes, including recurrent fever, rash, inflammatory arthritis, gastrointestinal symptoms and elevated inflammatory markers. All patients underwent molecular testing using a gene panel for periodic fever syndromes and were identified to carry NOD2 mutations associated with NOD2-associated autoinflammatory disease. Despite initially negative gastrointestinal evaluations, repeat endoscopy with duodenal tissue biopsy ultimately confirmed WD. After initial ceftriaxone and maintenance with doxycycline and/or HCQ, symptoms were largely controlled, though mild relapses occurred in follow-up. Conclusion: Both NOD2 and TW/WD are intensively involved in monocytes/macrophages. WD is regarded as a macrophage disease. NOD2 leucin-rich repeat-associated mutations in monocytes/macrophages cause functional impairment of these cells and consequently may make the host susceptible for TW infection and WD, especially in the setting of immunosuppression.