A NOVEL MUTATION DESCRIPTION IN LATE-ONSET PHENOTYPE CASE OF CONGENITAL THROMBOTIC THROMBOCYTOPENIC PURPURA (TTP)

PAIVA J; PRIMROSE, DEBORA M.; SANCHEZ LUCEROS, ANALIA; KEMPFER AC; CASINELLI MM; WOODS AI; LAZZARI MA

Melbourne

Congreso; XXVII Congress of the International Society on Thrombosis and Haemostasis (ISTH); 2019

International Society on Thrombosis and Haemostasis

BackgroundTTP is a generalized life-threatening disease due to deficiency in ADAMTS13 activity and in congenital TTP (cTTP) is due to mutations in the ADAMTS13 gene.AimWe described a novel mutation in combination with a known mutation in a patient (P) with a late-onset TTP phenotype.MethodsA 36-years-old female carrying the third pregnancy (20 weeks), with a history of two pregnancies loss, displayed microangiopathic hemolytic anemia with severe thrombocytopenia, that it was diagnosed as TTP. Laboratory assays: ADAMTS13 antigen and activity, IgG, IgM and IgA anti-ADAMTS13 (ELISA) and ultralarge von Willebrand factor multimers (ULVWF) (SDS-agarose gel electrophoresis). Sequencing was performed using ABI310 genetic analyzer. In silico analysis was evaluated using PolyPhen, SIFT, Mutations Taster, Panther, PROVEAN, ORFfinder and Expansy translate tools. The structure models for ADAMTS13 were obtained using CPHmodel 3.2 server, PatchDock, and interaction protein-protein by ClusPro. Molecular graphics were performed with the UCSF Chimera package. Informed consent and institutional ethical approval was obtained.ResultsWe found a novel mutation in heterozygous state in the exon 7 (c.794_803delGCAGCCGCCG), the translation results (ORFfinder and Expansy) and the analysis in Mutation Taster showed a change of the open-reading frames that induces a stop codon formation (p.Arg267Cysfs*2). Computational modeling of protein structures showed the absence of a great part of the C-terminus of ADAMTS13 affecting the interaction ADAMTS13-VWF. The second mutation was c.3178C>T (p.Arg1060Trp), previously reported (Tao Z et al, 2006).Conclusion Mutations in metalloprotease domain (MP) are shown to be related to absent/low ADAMTS13 activity. p.Arg267Cysfs*2 affects this MP domain, while the p.Arg1060Trp affects the thrombospondin type 1 (TSP1)-7 region. Both mutations may induce some residual ADAMTS13 activity and explain the late-onset phenotype of cTTP, as seen in our patient. Genetic testing, in silico simulation and protein modeling were helpful for an early diagnosis especially in women of childbearing age.