Background: Among F8 mutation types, main determinants of inhibitor development after replacement therapy in Hemophilia A, nonsense mutations display wide variation in the associated risk. Molecular mechanism of translational readthrough (Rdthr) at premature termination codons (PTCs), which produces traces of full-length factor VIII (FVIII) including missense and wild-type molecules (WT-Rdthr), may influence immune response and inhibitor formation risk. Methods: To provide a new classification of PTCs based on their susceptibility to inhibitor occurrence, we investigated F8 genotypes, inhibitor status and Rdthr features in 335 PTCs (1048 patients), recorded in the European Association for Haemophilia and Allied Disorders (EAHAD) database, and exploited recombinant FVIII expressionof PTC variants. In silico mean-differences in affinity of HLA-DR alleles for FVIII peptides and their missense counterparts, were calculated with NetMHCII. Results: The percentage of WT-Rdthr, hypothesized to minimize inhibitor development, was higher for patients affected by PTCs not associated with inhibitor, and was not predicted at all in patients with PTCs detected in at least three inhibitor-positive cases (n=136, p=0.0001). Among FVIII PTCs fused with luciferase, quantitative output of WT-Rdthr negative and positive groups did not differ, potentially highlighting forthe latter the importance of WT-Rdthr to prevent inhibitor onset.  Readthrough output was the lowest among WT-Rdthr negative PTCs highly associated with inhibitor. The WT Rdthr prediction was extended to all PTCs that could arise by single nucleotide variations for the entire F8 coding sequence. Estimated WT-Rdthr was higher in PTCs reported in EAHAD than those predicted (namely “predicted PTCs”, n=662), foreseeing a higher risk of developing inhibitors. In silico mean differences in affinity of HLA-DR alleles for FVIII peptides and their missense counterparts, potentially arising from Rdthr of PTCs without WT formation (n=297), were higher for missense variants predicted in patients with inhibitors than without (p<0.0001), and increased for PTCs present in more than one patient with inhibitor, supporting their immunogenic features. Conclusions: We provide a new genetic classification of HA PTCs that improves our knowledge about their relation with biological and clinical phenotypes, translatable to other human diseases, and potentially improve estimate of a graded PTC-related inhibitor risk in HLA genotyped patients.