The proband was initially misdiagnosed as myasthenia gravis. Based on the phenotype and family history, chronic progressive external ophthalmoplegia was suspected and confirmed by finding of a novel RRM2B variant. The detection of another truncating pathogenic variant in exon 9 of RRM2B further supports this exon as mutation hot spot and underlines the role of the C-terminal highly conserved amino acids for the interaction of the p53R2 dimer with the R1 dimer.
Mayer et al. (Sun,) studied this question.