AB0008 APPLYING WHOLE EXOME SEQUENCING TO FAMILIAL ANTIPHOSPHOLIPID SYNDROME: NEW PLAYERS IN A RARE DISEASE?
Authors: A. Barinotti, M. Radin, I. Cecchi, S. G. Foddai, E. Rubini, D. Roccatello, S. Sciascia, E. Menegatti
Journal: Annals of the Rheumatic Diseases (2021)

Background: Antiphospholipid Syndrome (APS) is an autoimmune disease whose precise aetiology is still unknown, but the high heterogeneity of its manifestations and clinical course is presumably due to the occurrence of different mechanisms and alterations at different levels and pathways [1]. The first genetic studies in APS focused primarily on the human leukocytes antigen system region, but more recent data highlighted a role of other genes in APS susceptibility, primarily those involved in the immune response and in the haemostatic process. Objectives: We aimed to deepen the investigation of APS genetic background starting from a case of familial APS, analysing two siblings with thrombotic APS (Table 1), both triple positive for antiphospholipid antibodies (aPL). Table 1. Main clinical and laboratory characteristics of the patients included in the study. Patient Age aPL Profile Relevant Clinical History 1 (F) 51 Triple positive (LA, aCL IgG, aβ2GPI IgG) Two episodes of ischemic stroke, one episode of CAPS (renal thrombotic microangiopathy, visual impairment, ischemic stroke) 2 (M) 47 Triple positive (LA, aCL IgG, aβ2GPI IgG) Three episodes of deep vein thrombosis, regardless ongoing well conducted therapy vitamin k antagonist and additional retinal vein thrombosis LA: lupus anticoagulant; aCL: anti-cardiolipin antibodies; aβ2GPI: anti- β2 glycoprotein I antibodies; CAPS: catastrophic APS. Methods: Genomic DNA was extracted from peripheral blood and the samples underwent Whole Exome Sequencing (WES). Sequencing was done on a 100X coverage, and reads have been aligned to the human reference genome (GRCh37/hg19 assembly) using the Burrows–Wheeler Alignment tool (BWA). The mean sequencing depth on target regions was 170X for patient 1, 205X for patient 2, moreover, 99.50% of the targeted bases had at least 10X coverage for all the three donors. The resulting single nucleotide polymorphisms (SNPs) have been analysed through a step-by-step process based on their frequency population (using Genome Aggregation Database), their predicted effects on the protein (using VarSome) and a literature research about the genes carrying them. Moreover, genes previously associated with a pro-thrombotic tendency and with APS have been analysed in the two patients. Results: Starting from more than 120000 SNPs for each patients, the analysis led to reduce the list of SNPs of interest to 27 missense mutations. The complete literature research regarding the genes carrying these mutations allowed to further reduce the number of selected genes, focusing on those that exert a role potentially involved in APS pathogenesis and development. In particular, these genes ( PLA2G6 , HSPG2 , BCL3 , ZFAT , ATP2B2 , CRTC3 and ADCY3 ) take part in the immune response and the vascular homeostasis. The list of the DNA missense variants of interest found in our cases of familial APS is resumed in Figure 2. Figure 2. List of DNA missense variants of interest found in patient 1 and 2. Genes potentially involved in APS pathogenesis and development are highlighted in bold. No mutations on genes known to be associated with a pro-thrombotic state ( F5 , F2 , MTHFR , F13A1 , PROC , PROS1 , FGB and SERPINE1 ), or on genes previously associated with APS ( B2GPI , PF4V1 , SELP , TLR2 , TLR4 , GP Ia , GP1BA , F2R , F2RL1 , TFPI , F3 , VEGFA , FLT1 , and TNF ) have been found in the WES analysis. Conclusion: To some extent, this can be seen as a proof of concept of the complexity of APS. Efforts to interpret the genetic risk factors involved in the heterogeneous clinical features of the syndrome, for instance, the integration of WES and network-based approaches might help to identify and stratify patients at risk of developing APS. References: [1]Iuliano A, Galeazzi M, Sebastiani GD. Antiphospholipid syndrome’s genetic and epigenetic aspects. Autoimmun Rev. 2019;18(9). Disclosure of Interests: None declared