Phenotype and genotype of FXIII deficiency in two unrelated probands: identification of a novel F13A1 large deletion mediated by complex rearrangement

Siyu Ma,Wenman Wu,Yan Liu,Xuefeng Wang,Qiulan Ding,Xi Wu,Changming Chen,Qian Liang

doi:10.1186/s13023-019-1144-z

Siyu Ma, Wenman Wu + Show 6 more

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https://doi.org/10.1186/s13023-019-1144-z

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Abstract

BackgroundInherited Factor XIII deficiency (FXIIID) is one of the most severe and under-diagnosed rare bleeding disorders. Only 5 large deletions involving one or more exons in F13A1 have been reported, and lacking of multiplex ligation-dependent probe amplification (MLPA) assay might underestimate the copy number variations (CNVs) in F13A1 and F13B. We had characterized the clinical presentation of two unrelated severe FXIIID probands and explored the pathogenic mechanisms.ResultsBoth probands experienced several episodes of fatal bleeding and delayed wound healings prior to diagnosis. FXIII activity was measured by the ammonia release assay, and FXIII-A and FXIII-B antigens were determined by ELISA. All the exons including exon-intron boundaries and promoter regions of F13A1 and F13B were amplified and directly sequenced. Copy number variations (CNVs) of F13A1 and F13B were detected by the CNVplex® method. Breakpoints of the F13A1 large deletion were identified by quantitative primer walking combined long-range PCR (LR-PCR) strategies. Proband 1 was found to have compound heterozygous mutations of a novel small deletion (c.1147del) and a missense mutation p.Arg383Ser. Proband 2 was compound heterozygous for a novel large deletion (g.[77815_112815del;112837_116628del]) and a missense mutation p.Arg716Gly in F13A1. Bioinformatics analysis of the large deletion breakpoints predicted that two fork stalling and template switching and/or microhomology-mediated break-induced replication (FoSTeS/MMBIR) events with two homologies of TCT and C might be responsible for the complex rearrangement. Prophylactic replacement therapy was immediately administered for the two probands upon establishment of the diagnosis.ConclusionsWe detected two type I FXIIID pedigrees and adopted CNVplex® method to detect CNVs of F13A1 and F13B for the first time. A large heterozygous deletion of g.[77815_112815del;112837_116628del] in F13A1, mediated by two FoSTeS/MMBIR events, was identified.

Highlights

Inherited Factor XIII deficiency (FXIIID) is one of the most severe and under-diagnosed rare bleeding disorders
FXIII zymogen is activated into its enzyme form FXIIIa, by thrombin in the presence of Ca2+.The cleavage of the activation peptide results in A and B subunits dissociation, which is accelerated by the presence of fibrin [3]
Type I FXIIID-A is a quantitative deficiency of FXIIIA, while type II is a functional defect of FXIII-A with almost normal concentration [5]

Summary

Introduction

Inherited Factor XIII deficiency (FXIIID) is one of the most severe and under-diagnosed rare bleeding disorders. 5 large deletions involving one or more exons in F13A1 have been reported, and lacking of multiplex ligation-dependent probe amplification (MLPA) assay might underestimate the copy number variations (CNVs) in F13A1 and F13B. Hereditary FXIII deficiency (FXIIID) is a rare bleeding disorder with a prevalence of one per two million individuals. Type I FXIIID-A is a quantitative deficiency of FXIIIA, while type II is a functional defect of FXIII-A with almost normal concentration [5]. Because multiplex ligation-dependent probe amplification (MLPA) or other CNV detection methods were not available for screening large deletions or duplications in F13A1 and F13B, the number of these variants might be underestimated. A generation sequencing (NGS) panel involving F13A1 and F13B was established, which can screen CNVs and other mutations [14]

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