Characterization of F8 defects in haemophilia A in Pakistan: investigation of correlation between mutation type and the in vitro thrombin generation assay

Abstract

Hereditary haemophilia A is an X-linked bleeding disorder caused by mutations in the coagulation factor VIII gene (FVIII abbreviates protein, gene symbol F8). The mutation spectrum has been reported in various populations but not in Pakistan. The aims of this study were to (i) characterize F8 mutations in a large haemophilia A cohort from Pakistan and to (ii) investigate whether in vitro thrombin generation (TG) differs according to mutation type (null compared with missense) in severe haemophilia A. One hundred individuals diagnosed with haemophilia A and 100 healthy controls were recruited in Pakistan. Phenotypic measurements were re-evaluated in Cardiff; the essential regions of F8 were screened for the causative defect. A diagnosis of haemophilia A was confirmed for 92 individuals, 7 were found to have haemophilia B and 1 did not have haemophilia. The F8 defects were characterized for 80 of the 92 haemophilia A individuals and comprised point mutations, inversions (intron 22 and intron 1) and frameshifts. Point mutations (41%) were the most frequent, followed by the intron 22 inversion (20%). Thirty novel variants were identified. Comparison of in vitro TG parameters [velocity index (VI) and peak] was made between severe individuals who had a null mutation (no FVIII) and those with a missense change (dysfunctional FVIII), no significant difference was observed. The spectrum of F8 defects in Pakistan is heterogenous; VI and peak in severe haemophilia A are not influenced by whether the underlying mutation gives rise to dysfunctional FVIII or no coagulation factor at all.

Joint health scores in a haemophilia A cohort from Pakistan with minimal or no access to factorVIIIconcentrate: correlation with thrombin generation and underlying mutation

“…Thus, although the mutation is the basis of the disorder, in severe individuals the nature of the gene defect does not correlate with the degree of arthropathy. This is consistent with the findings of the TG studies, additionally we have previously shown that in severe haemophilia, TG is not associated with the F8 mutation [14].…”

“…Ninety‐two individuals with hereditary haemophilia A, originating from all five provinces of Pakistan, were recruited as previously described . The haemophilia A cohort consisted of mild, moderate and severe individuals.…”

A basis for prenatal diagnosis of Haemophilia-A in Pakistani patients

“…Phenotypic severity is characterized by factor VIII plasma level: severe phenotype having plasma levels of <1%whereas moderate and mild phenotypes having plasma levels of 1-5% and 5-30% respectively. 10 Keeping in view difficulties in management, high cost of treatment and low Health related quality of life of haemophilia patients, prevention of the disease is the most viable and practical option. Prevention through prenatal diagnosis by Muhammad Arif Sadiq et al molecular diagnostic approaches includes linkage based analysis and direct variant analysis of disease causing variants.…”

Optimization of the thrombin generation test components to measure potency of factor VIII concentrates

“…Despite several promising reports of reduced TGT in haemophiliacs with severe bleeding tendencies [13,15,[35][36][37], the predictive value of the method remains controversial. For example, a number of recent studies have shown a lack of correlation between TGT values and such clinically relevant determinants as severity of bleeding phenotype [3, [38][39][40][41], presence of anti-FVIII inhibitors [38], type of FVIII gene mutation (null mutation vs. missense change [41]) and effectiveness of inhibitor bypass therapy [42]. We hypothesize that the unfavourable outcome of the TGT application could be in part related to the use of suboptimal TGT assay conditions.…”