A novel hypomorphic splice variant in EIF2B5 gene is associated with mild ovarioleukodystrophy

OBJECTIVE: To identify the genetic cause in an adult ovarioleukodystrophy patient resistant to diagnosis. METHODS: We applied whole‐exome sequencing (WES) to a vanishing white matter disease patient associated with premature ovarian failure at 26 years of age. We functionally tested an intronic variant by RT‐PCR on patient’s peripheral blood mononuclear cells (PBMC) and by minigene splicing assay. RESULTS: WES analysis identified two novel variants in the EIF2B5 gene: c.725A > G (p.Tyr242Cys) and an intronic noncanonical mutation (c.1156 + 13G>A). This intronic mutation resulted into generation of various isoforms both in patient’s PBMC and in the minigene splicing assay, showing that ~20% residual wild‐type isoform is still expressed by the intronic‐mutated allele alone, concordant with an hypomorphic effect of this variant. CONCLUSION: We report two novel variants in EIF2B5, one of them a noncanonical intronic splice variant, located at a +13 intronic position. This position is mutated only in 0.05% of ClinVar intronic mutations described so far. Furthermore, we illustrate how minigene splicing assay may be advantageous when validating splice‐altering variants, in this case highlighting the coexistence of wild‐type and mutated forms, probably explaining this patient’s milder, late‐onset phenotype.