Activation of a cryptic splice site in a potentially lethal coagulation defect accounts for a functional protein variant

► + 1G donor splice site mutations virtually suppress correct gene expression. ► Complete deficiency of coagulation factor VII (FVII) is lethal. ► The F7 IVS6 + 1G/T induces exon skipping and use of an in-frame cryptic 5'ss. ► The latter transcript encoded a protein lacking 10 residues in the activation domain. ► The residual activity of this variant might have reverted a lethal condition.