Search

The inherited deficiency of ADAMTS13 is usually associated with severe forms of thrombotic thrombocytopenic purpura. Among the mutations identified in the ADAMTS13 gene, none have been described on the TSP1-6 repeat domain. We investigated an Iranian family with a history of chronic recurrent thrombotic thrombocytopenic purpura, severe ADAMTS13 deficiency and a heterogeneous pattern of clinical symptoms among affected members. Genetic analysis revealed a homozygous deletion of nucleotides 2930-2935 (GTGCCC) in exon 23 of ADAMTS13, leading to the replacement of Cys977 by a Trp and the deletion of Ala978 and Arg979 in the TSP1-6 repeat domain. To explore the mechanism of ADAMTS13 deficiency, in vitro expression studies were performed. Western blotting, pulse-chase labeling and immunofluorescence studies demonstrated a secretion pathway defect of the mutant protein, with no intracellular accumulation. This finding is consistent with the severe ADAMTS13 deficiency but does not explain the heterogeneous clinical picture of the 3 siblings carrying the same mutation.

Background: Factor V deficiency is a rare autosomal recessive hemorrhagic disorder, associated with bleeding manifestations of variable severity. In the present study, we investigated the molecular basis of factor V deficiency in three patients, and performed a comprehensive analysis of the factor V gene (F5) splicing pattern., Design and Methods: Mutational screening was performed by DNA sequencing. Wild-type and mutant F5 mRNA were expressed by transient transfection in COS-1 cells, followed by reverse-transcriptase polymerase chain reaction and sequencing. Real-time reverse-transcriptase polymerase chain reaction was used to evaluate degradation of mRNA carrying premature termination codons., Results: Mutational screening identified three hitherto unknown splicing mutations (IVS8+6T>C, IVS21+1G>A, and IVS24+1_+4delGTAG). Production of mutant transcripts in COS-1 cells demonstrated that both IVS21+1G>A and IVS24+1_+4delGTAG cause the activation of cryptic donor splice sites, whereas IVS8+6T>C causes exon-8 skipping (F5-Delta 8-mRNA). Interestingly, F5-Delta 8-mRNA was also detected in wild-type transfected samples, human liver, platelets, and HepG2 cells, demonstrating that F5 exon-8 skipping takes place physiologically. Since F5-Delta 8-mRNA bears a premature termination codons, we investigated whether this transcript is subjected to nonsense-mediated mRNA decay degradation. The results confirmed the involvement of nonsense-mediated mRNA decay in the degradation of F5 PTC(+) mRNA. Moreover, a comprehensive analysis of the F5 splicing pattern led to the identification of two in-frame splicing variants resulting from skipping of exons 3 and 5-6., Conclusions: The functional consequences of three splicing mutations leading to FV deficiency were elucidated. Furthermore, we report the identification of three alternatively spliced F5 transcripts.

Factor X deficiency is a severe rare hemorrhagic condition inherited as an autosomal recessive trait. It is one of the most severe recessive inherited coagulation disorders. We analyzed the clinical manifestations, laboratory phenotype and genotype in 10 patients with severe Factor X deficiency and in their heterozygous relatives. The most frequent bleeding episodes were hematomas (70%) and gum bleeding (60%). Fifty percent of the homozygous patients required blood transfusion and one-third of heterozygotes required treatment after surgery or delivery. The genetic characterization revealed six different missense mutations, two of which were novel: p.Glu69Lys and p.Asp103His. Haplotype analysis, performed with intra- and extra- FX gene polymorphic markers in Indian, Iranian and Italian patients with the same mutations failed to establish identity by descent, despite the same Caucasian origin. In conclusion, factor X deficiency was confirmed to be one of the most serious among rare bleeding disorders and genetically heterogeneous in different populations.