Deficiency in the A-subunit of coagulation factor XIII: two novel point mutations demonstrate different effects on transcript levels

Abstract

Congenital deficiency in coagulation factor XIII is a rare autosomal recessive bleeding disorder. Although the defect was characterized over 30 years ago, little is known about the molecular basis of the disorder. Here, we show two novel point mutations in the gene of the A- subunit of factor XIII in the genetically isolated population of Finland. All eight factor XIII-deficient families identified in Finland were studied. The exons of the gene of A-subunit were amplified individually by polymerase chain reaction and subsequently screened by single-strand conformation polymorphism. Sequence analysis of the abnormally migrating fragments showed two point mutations resulting in an amino acid alteration. A C-to-T transition at Arg-661 in exon XIV created a premature stop codon. This mutation was detected in six of the eight families, thus being the major alteration causing FXIII deficiency in Finland. In two of the six families, the patients were compound heterozygotes with the Arg-661-Stop mutation in one allele and either a T-to-C point mutation in exon VI or a thus far uncharacterized mutation in the other allele. The T-to-C transition in exon VI resulted in a substitution of threonine for methionine 242. The transition was found in one family only, where it was in the heterozygote form combined with the Arg-661-Stop mutation. To evaluate the consequences of these mutations, steady-state FXIII mRNA levels were quantitated by solid-phase minisequencing. In addition to the termination of translation 70 amino acids before the initial stop codon, the Arg-661- Stop mutation causes a 10- to 30-fold reduction in FXIII mRNA levels. This is also likely to result in a low translation level in the truncated polypeptide. In contrast, Met-242-Thr mutation does not seem to affect the level of mRNA. Here, the absence of a functional and immunodetectable protein is probably caused by an altered conformation of the mutant polypeptide, resulting in early degradation of the defective protein.

Val34Leu polymorphism of plasma factor XIII: biochemistry and epidemiology in familial thrombophilia

“…These values are comparable to the data reported in the literature. 9,37 As shown in Table 1, 10.4% of the controls and 24.2% of the patients with familial thrombophilia carried the FV Leiden mutation in the heterozygous form. The high percentage of FV Leiden in the control group represents the high frequency of FV Purified plasma FXIII was activated by thrombin for 5 minutes at 37°C.…”

“…5,6 In addition to pathogenic mutations, a number of polymorphisms have been identified in the amino acid sequence of FXIII-A. [7][8][9][10] The biochemical effect of these polymorphisms has not been explored. One of them, a Val to Leu change, occurs at position 34 in the AP, just 3 amino acid residues away from the thrombin activation site (Arg37-Gly38).…”

“…One of them, a Val to Leu change, occurs at position 34 in the AP, just 3 amino acid residues away from the thrombin activation site (Arg37-Gly38). 9 A protective effect against myocardial infarction [11][12][13] and thrombotic cerebral artery occlusion 14 has been attributed to the Leu34 allele. Protection against venous thrombosis by the Leu34 allele has also been reported.…”

Gene Defects in Congenital Factor XIII Deficiency

“…Mikkola and coworkers have also quantitated the mRNA levels by solid phase minisequencing, which fa cilitates allele-specific quantitation of mRNA levels. 20 ' 26 The quantity of mRNA is often reduced in nonsense mutations that result in premature termination of transla tion. This is probably due to altered stability or processing and nucleocytoplasmic transport of the mRNA (for a review, see Cooper 29 ).…”

“…Since then, more mutations have been identified providing a view of the molecular genetic background of the disease. So far, almost 20 different mutations have been reported in the gene of the catalytic A-subunit of factor XIII [15][16][17][18][19][20][21][22][23][24][25][26] (Fig. 1) and 3 mutations in the gene of the carrier protein B-subunit.…”