F8variants and their genotype-phenotype correlations in Thai patients with haemophilia A: a nationwide multicentre study

Abstract

AimsAnalysis of theF8gene helps predict the risk of developing factor VIII (FVIII) inhibitors and the depth of phenotype in haemophilia A (HA) patients. Since data in Southeast Asian countries remain scarce, we aim to studyF8variation correlated with HA phenotypes in Thailand.MethodsThai patients with HA were enrolled from seven haemophilia treatment centres during 2022–2023. Using peripheral blood DNA, inverse shifting-polymerase chain reaction (IS-PCR) forF8-intron 22 inversion (Inv22) andF8-intron 1 inversion (Inv1) was performed. Whole exome sequencing (WES) was explored in cases without Inv22/Inv1.ResultsOf 124 patients with HA, 91.9% were detected with a causativeF8variant, including Inv22 (30.6%), Inv1 (1.6%), missense (23.4%), nonsense (16.9%) and small insertion/deletion (16.1%) mutations. Inv22, small insertion/deletion and nonsense were associated with severe HA, compared with missense variants, by the ORs of 13.9 (95% CI, 4.2 to 56.7), 14.7 (95% CI, 3.4 to 104.7) and 15.6 (95% CI, 3.6 to 110.2), respectively. While nonsense variants affecting the light chain increased the risk of developing FVIII inhibitors (OR, 6.8; 95% CI, 1.5 to 32.6) compared with the low-risk (small insertion/deletion, missense and splice-site) variants. Twelve patients (9.7%) harboured novelF8variants, comprising five missense (p.Pro540Leu, p.Ser564Pro, p.Leu668Pro, p.Ala1721Glu, p.His2024Pro), five small insertion/deletion (p.Val502SerfsTer13, p.Ile522PhefsTer13, p.Phe992LysfsTer11, p.Leu1223PhefsTer18, c.6427_6429+3delATGGTA) and one nonsense mutations (p.Glu1292Ter).ConclusionsIS-PCR followed by WES successfully assessesF8alterations in most HA cases. With several unique variants, severe HA in Thailand is considerably caused by Inv22, small insertion/deletion and nonsense, whereas missense variants are more responsible for nonsevere HA phenotypes.