Genetic testing of Behçet's disease using next-generation sequencing to identify monogenic mimics and HLA-B*51

Objective: Several monogenic autoinflammatory disorders and primary immunodeficiencies can present early in life with features that may be mistaken for Behçet's disease (BD). We aimed to develop a genetic analysis workflow to identify rare monogenic BD-like diseases and establish the contribution of HLA haplotype in a cohort of patients from the UK.

Methods: Patients with clinically suspected BD were recruited from four BD specialist care centres in the UK. All participants underwent whole exome sequencing (WES), and genetic analysis thereafter by 1. examining genes known to cause monogenic immunodeficiency, autoinflammation or vasculitis by virtual panel application; 2. scrutiny of variants prioritised by Exomiser using Human Phenotype Ontology (HPO); 3. identification of copy number variants using ExomeDepth; and 4. HLA-typing using OptiType.

Results: Thirty-one patients were recruited: median age 15 (4-52), and median disease onset age 5 (0-20). Nine/31 (29%) patients had monogenic disease mimicking BD: 5 cases of Haploinsufficiency of A20 with novel TNFAIP3 variants (p.T76I, p.M112Tfs*8, p.S548Dfs*128, p.C657Vfs*14, p.E661Nfs*36); 1 case of ISG15 deficiency with a novel nonsense variant (ISG15:p.Q16X) and 1p36.33 microdeletion; 1 case of Common variable immune deficiency (TNFRSF13B:p.A181E); and 2 cases of TNF receptor associated periodic syndrome (TNFRSF1A:p.R92Q). Of the remaining 22 patients, 8 (36%) were HLA-B*51 positive.

Conclusion: We describe a novel genetic workflow for BD, which can efficiently detect known and potentially novel monogenic forms of BD, whilst additionally providing HLA-typing. Our results highlight the importance of genetic testing before BD diagnosis, since this has impact on choice of therapy, prognosis, and genetic counselling.