Comprehensive Targeted Sequencing Identifies Monogenic Disorders in Patients With Early‐onset Refractory Diarrhea

ABSTRACT Objectives: Causes of early‐onset refractory diarrhea include exudative diarrhea associated with very early‐onset inflammatory bowel diseases, osmotic or secretory diarrhea, and protein‐losing enteropathy. Monogenic disorders are included in these diseases, yet a comprehensive genetic analysis has not been fully established. Methods: We established targeted gene panels covering all responsible genes for early‐onset diarrhea. In total, 108 patients from 15 institutions were enrolled in this study. We collected clinical data from all patients. Seventy‐three patients with exudative diarrhea, 4 with osmotic or secretory diarrhea and 8 with protein‐losing enteropathy were subjected to genetic analysis. Results: A total of 15 out of the 108 enrolled patients (13.9%) were identified as monogenic. We identified 1 patient with RELA , 2 with TNFAIP3 , 1 with CTLA4 , 1 with SLCO2A1 , 4 with XIAP , 3 with IL10RA , 1 with HPS1 , 1 with FOXP3 , and 1 with CYBB gene mutations. We also identified 1 patient with NFKB2 and 1 with TERT mutations from the gene panel for primary immunodeficiency syndromes. The patient with refractory diarrhea caused by heterozygous truncated RelA protein expression is the first case identified worldwide, and functional analysis revealed that the mutation affected nuclear factor kappa B signaling. Genotypes were significantly associated with the clinical and pathological findings in each patient. Conclusions: We identified variable monogenic diseases in the patients and found that genes responsible for primary immunodeficiency diseases were frequently involved in molecular pathogenesis. Comprehensive genetic analysis was useful for accurate molecular diagnosis, understanding of underlying pathogenesis, and selecting the optimal treatment for patients with early‐onset refractory diarrhea. An infographic for this article is available at: http://links.lww.com/MPG/B853 .