Factor VIII genotype characterization of haemophilia A affected patients with transient and permanent inhibitors: a comprehensive Argentine study of inhibitor risks

Abstract

Inhibitor development against exogenous factor VIII is a severe impairment of replacement therapy affecting 18% of Argentine patients with severe haemophilia A (HA). To study the molecular predisposition for inhibitor development, we genotyped 260 HA patients with and without inhibitors, countrywide. The inhibitor-positive population (19 transients, 15 low responders, LR and 70 high responders, HR) of 104 severe-HA patients showed 59 Inv22 (intron 22 inversions), 18 small ins/del-frameshifts, 12 gross deletions, 12 nonsense, one splicing defect and two missense, p.Arg531Pro and p.Leu575Pro, both LR and thought to impair FVIII A2 domain secondary structure. In addition, a patient with mild HA and HR showed the missense p.Glu1704Lys associated with two neutral intronic substitutions potentially affecting the A3 domain. A case/control study (84/143) permitted estimation of F8 genotype-specific inhibitor risks [OR; prevalence (CI)] in severe-HA patients classifying a high-risk group including multi-exon deletions [3.66; 55% (19-100)], Inv22 [1.8; 24% (19-100)] and nonsense in FVIII-LCh [1.2; 21% (7-59)]; an average risk group including single-exon deletions, indel frameshifts and nonsense-HCh; and a low-risk group represented by missense defects [0.14; 3% (0.6-11)]. Analysis of inhibitor concordance/discordance in related patients indicated additional genetic factors other than F8 genotype for inhibitor formation. No significant inhibitor-predisposing factors related to FVIII product exposure were found in age- and F8 genotype-stratified populations of severe-HA patients. In conclusion, the Argentine HA patient series presents similar global and mutation-specific inhibitor risks than the HA database and other published series. This case-specific information will help in designing fitted therapies and follow-up protocols in Argentina.

A prevalent CTLA4 missense variant significantly associates with inhibitor development in Argentine patients with severe haemophilia A

“…The choice of Inv22-positive severe HA patients to investigate secondary genetic factors predisposing for inhibitor development was based on two main reasons. First, because the Inv22-positive population provides the biggest number of perfectly homogeneous group of severe HA patients associated with significant chances to develop inhibitors against therapeutic FVIII, fact that was estimated in previous studies in our population [2] and confirmed in this study. Second, and perhaps more importantly, it was proved that the Inv22-mutated F8 expresses the entire FVIIIamino-acid sequence intracellularly (two non-secreted polypeptides result in a positive intracellular FVIIIcross reacting material); thus, differentiating from genuine null mutations and becoming 'pharmacogenetically relevant' affecting its high-moderate inhibitor risk by the nature of the administered therapeutic FVIII [11].…”

“…Once the results of the analysis of inhibitor status concordance among familiarly related HA patients unveiled the possible involvement of secondary genetic factors in our population [2], the choice of a list of candidate genes and polymorphisms came naturally supported by the net of molecules involved in this specific immune response, the significant associations found in other populations and the SNP frequency distribution associated with 26 ethnic groups worldwide showed in the 1000 Genomes Project [12].…”

“…Among the former, environmental risk factors include treatment-related factors and immune-system challenges. Among the latter, in HA, the causative F8 genotype has been established as the main factor conditioning inhibitor development (in Argentina [2], and worldwide, reviewed in [3]), but it also counts a group of secondary risk factors, weaker than the F8 genotype, such as family history of inhibitors, ethnicity, human lymphocyte antigen haplotype and polymorphisms linked to immune-system genes, such as Interleukin-10 (IL10), tumour necrosis factor-a (TNFA) and cytotoxic T-lymphocyte associated protein-4 (CTLA4) [4,5]. Human genetics evidence indicates that predisposing factors associated with autosomal genes, such as those mentioned above, are ethnically dependent and therefore not consistent among populations worldwide.…”

“…In this scenario and encouraged by previous studies of inhibitor concordance in familiarly related patients indicating the possible presence of additional genetic factors (others than the F8-genotype) in our population [2], we screened for locally relevant secondary inhibitor risk factors in a relatively large homogeneous population of patients with the Inv22 and a comprehensive severe HA population.…”

Reliable and cost‐effective approach for diagnosis of heterozygous F8/F9 large deletions by quantitative real‐time PCR

“…We have recently estimated the F8/F9 genotype associated inhibitor risks in Argentine patients with HA and HB, and found inhibitor odds ratios, OR (CI95), of 3.66(1.07-12.55) for F8-multi-exon deletions, and 32.7(2.26-471) for deletions on the entire F9 respectively [2,10]. Inhibitor development impacts the quality of life of patients with haemophilia and the National health care system because of the higher costs involved for their specific treatment.…”