Functional studies associate novel DUOX2 gene variants detected in heterozygosity to Crohn's disease

Crohn's disease is a chronic gastrointestinal inflammatory disease with possible extraintestinal symptoms. There are predisposing genetic factors and even monogenic variants of the disorder. One of the possible genetic factors are variants of the DUOX2 gene. The protein product of the DUOX2 gene is a dual oxidase enzyme producing H₂O₂ in the bowel. Reduced H₂O₂ levels impact mucosal homeostasis and contribute to the development of inflammatory bowel disease. Thus far, only 19 patients with IBD with the DUOX2 variants have been described.

Here we present a case report of an adolescent female diagnosed at eleven years of age with IBD that was subsequently reclassified as Crohn's disease. She was treated with immunosuppressants and biological therapy but experienced additional complications. Her peripheral blood lymphocyte DNA was studied using massive parallel sequencing. Detected variants were functionally studied.

Whole exome sequencing found two novel DUOX2 gene variants: a de novo variant c.3646C>T; p.R1216W and a maternally inherited variant c.3391G>A; p.A1131T which were initially classified as variants of unknown significance. However, follow-up functional studies demonstrated that both DUOX2 variants led to impaired H₂O₂ generation, which led to their reclassification to the likely pathogenic class according to the ACMG.net. Therefore, we conclude that these variants are causative for the disease.

Identifying novel variants in patients with Crohn's disease and their families is important for precision medicine approaches and understanding of the pathogenesis of likely "monogenic" rare forms of inflammatory bowel disease.