bioRxiv preprint doi: https://doi.org/10.1101/532804; this version posted January 28, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 1 2 3 RE-EVALUATION OF MEFV GENE VARIANTS: UTILITY OF A GENE SPECIFIC THRESHOLD IN REDUCING THE 4 NUMBER OF VARIANTS OF UNKNOWN SIGNIFICANCE 5 6 Matteo Accetturo1, Angela Maria D’Uggento2, Piero Portincasa3, Alessandro Stella4* 7 8 9 1 R&D Department, BioTechnology Services srl, Foggia, Italy 10 11 2 Department of Economics and Finance, Università degli Studi di Bari Aldo Moro, BARI, Italy 12 13 3 Division of Internal Medicine, 2a Clinica Medica A. Murri, Department of Biomedical Sciences and Human 14 Oncology, Università degli Studi di Bari Aldo Moro, AOU Policlinico di Bari, BARI, Italy 15 16 4 Laboratory of Medical Genetics, Department of Biomedical Sciences and Human Oncology, Università 17 degli Studi di Bari Aldo Moro, AOU Policlinico di Bari, BARI, Italy 18 19 20 *Corresponding author: Dr. Alessandro Stella, Department of Biomedical Sciences and Human Oncology, 21 Università degli Studi di Bari Aldo Moro, AOU Policlinico di Bari, P.zza G. Cesare 11 70124 BARI, Italy 22 email: [email protected] 23 24 25 bioRxiv preprint doi: https://doi.org/10.1101/532804; this version posted January 28, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 26 Abstract 27 Familial Mediterranean Fever (FMF) is an inherited autoinflammatory syndrome caused by mutations in the 28 MEFV gene. MEFV variants are still in large part classified as variant of uncertain significance (VOUS), or 29 with classification unresolved, posing significant challenges in the clinical diagnosis of Familial 30 Mediterranean Fever (FMF). REVEL is a recently developed variant metapredictor tool. To reduce the 31 number of MEFV variants with ambiguous classification we extracted the REVEL score for all missense 32 variants reported at the locus specific database INFEVERS, and analyzed its correlation with expert-based 33 classification and localization in the MEFV-encoded pyrin protein functional domains. 34 The data set of 216 missense variants was divided in four classification categories (BENIGN, VOUS, 35 PATHOGENIC and UNRESOLVED). MEFV variants were plotted onto the pyrin protein, the distribution of 36 REVEL scores in each category was computed and means, confidence intervals, and area under the receiver 37 operating curve were calculated. 38 We observed a non-random distribution of pathogenic variants along the functional domains of the pyrin 39 protein. The REVEL scores demonstrated a good correlation with the consensus classification of the 40 International Study Group for Systemic Autoinflammatory Diseases (INSAID). Sensitivity, specificity, and 41 accuracy were calculated for different cutoff values of REVEL scores and a gene-specific threshold was 42 computed with confidence boundary limits. A REVEL score of 0.298 was the best performing cut-off to 43 reclassify 96 MEFV gene variants previously of uncertain significance or unsolved thus reducing their 44 proportion from 61.6% to 17.6%. 45 In conclusion, the combination of available expert information with highly sensitive predictor tools yields to 46 more accurate interpretation of clinical consequences of MEFV gene variants. This approach should bring to 47 a better genetic counseling and patient management. 48 49 2 bioRxiv preprint doi: https://doi.org/10.1101/532804; this version posted January 28, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 50 Author summary 51 We aimed to refine MEFV gene variants classification using the metapredictor REVEL. We demonstrate that 52 a gene-specific threshold is effective for accurate variants’ classification. Using this threshold, we reduced 53 significantly the proportion of MEFV variants with an ambiguous classification. The proposed classification 54 could represent a useful resource for variant interpretation in the context of FMF diagnosis. 3 bioRxiv preprint doi: https://doi.org/10.1101/532804; this version posted January 28, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 55 Introduction 56 Familial Mediterranean Fever (FMF) is the most common of the Hereditary recurrent fevers (HRFs) with an 57 estimated prevalence of 1 in 1-5/ 10 000. FMF has been first described more than sixty years ago [1,2], and 58 since the identification of the causative gene (MEFV, NM_000243.2) it has been intensively studied [3,4]. 59 The MEFV gene encodes for an 86 kDa protein (Pyrin or marenostrin, TRIM20) prevalently expressed in 60 immune cells (neutrophils, eosinophils, monocytes, dendritic cells and synovial fibroblasts), and is related 61 to abnormal response of the innate immune system and IL-1β during periodic attacks of fever and serositis 62 [5,6]. In spite of several reports describing large FMF patients’ datasets, a complete understanding of the 63 pathogenic mechanisms responsible for this disease has not been reached yet. Recent studies suggested 64 the possibility of dominant inheritance, at least for some mutations. This hypothesis is casting doubts on 65 the traditional autosomal recessive mode of inheritance [7-10], a paradigm in FMF for long time. For FMF, a 66 well-curated locus specific database is available at INFEVERS (https://infevers.umai-montpellier.fr/web/), 67 containing genotype and clinical information for more than 500 variants. Recently, the International Study 68 Group for Systemic Autoinflammatory Diseases (INSAID) has critically reviewed the clinical information for 69 858 variants in the four genes (MEFV, TNFRSF1A, NLRP3 and MVK) responsible for hereditary recurrent 70 fevers (HRFs) reaching a consensus classification for 94% of variants analyzed [11]. The notable exception 71 was represented by the MEFV gene, where only 55.7% of the variants could be successfully classified with 72 almost a third of them being variants of unknown significance (VOUS). As a result, clinicians face the harsh 73 reality of frequently receiving an inconclusive genetic referral for FMF diagnosis. Internationally recognized 74 guidelines have been reported by the American College of Medical Genetics (ACMG) and the Association 75 for Molecular Pathology (AMP) [12], providing a five-tier classification of genetic variants in: pathogenic (P), 76 likely pathogenic (LP), variant of uncertain significance (VOUS or VUS), likely benign (LB), and benign (B). 77 However, since even the mode of inheritance in FMF families has been recently jeopardized by several 78 reports of apparently dominant mutations, the ACMG/AMP guidelines might be of limited value in FMF. In 79 this work, we used REVEL (a recently developed ensemble method which has been demonstrated to 80 outperform most commonly used web-based predictors) [13], to improve the classification of many 4 bioRxiv preprint doi: https://doi.org/10.1101/532804; this version posted January 28, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 81 unsolved, unclassified, or of uncertain significance MEFV gene variants. We also report a non-random 82 distribution of variants along the coding sequence of the MEFV gene. This observation possibly identifies 83 novel hotspots for variants with a putative pathogenic role. 84 Results 85 Non-random distribution of variants. The REVEL score was extracted for all the 216 missense variants 86 present at the INFEVERS database. Each variant was mapped along the coding sequence of MEFV gene, and 87 with respect to the functional domains of the pyrin protein (Fig 1). We observed that PATHOGENIC variants 88 (as defined in the methods) clustered in the SPRY and zf-B_box domains. In contrast, BENIGN variants were 89 markedly underrepresented in functional domains of the pyrin protein being localized, in large majority, in 90 the exon 2 of the MEFV gene. Finally, VOUS occurred along the entire coding sequence of the MEFV, 91 whereas distribution of UNRESOLVED variants appeared to mostly overlap with the PATHOGENIC one. 92 REVEL variants score. The means of REVEL scores for BENIGN (n=41, 0.18), VOUS (n=89, 0.25), 93 PATHOGENIC (n=41, 0.39) and UNRESOLVED (n=44, 0.31) variants showed statistically significant 94 differences among the four categories (F 21.04 p<0.0001, ordinary one-way ANOVA) demonstrating an 95 appreciable level of correspondence between the INSAID consensus-based variant classification and an in 96 silico computational scoring method such as REVEL (Fig 2). The results of unpaired t-tests among each 97 category demonstrated statistically significant differences between BENIGN and UNRESOLVED, BENIGN and 98 PATHOGENIC, and VOUS vs PATHOGENIC (Fig 2). Only one variant classified by INSAID as benign or likely 99 benign had an unexpectedly high pathogenic score (E230Q, 0.737, identified as an outlier using ROUT 100 method). In contrast, 28 of 41 INSAID pathogenic or likely pathogenic variants had a score below the REVEL 101 threshold for pathogenicity (<0.4).[15] Worthy of note, the M694V variant, considered to be responsible for 102 the most severe FMF phenotype, barely reached the threshold for pathogenicity (REVEL score 0.403). 103 Finally, the area under the ROC curve (AUC) was 0.879 (p<0.0001, Fig 3) 104 Development of a new classifier and reclassification of MEFV variants.