KRT4 and early-onset parkinsonism-intellectual disability syndrome: The aim of this study is to report 4 new cases of WSN, comparing the results from non-invasive diagnostic techniques (oral brush Thin Prep for exfoliative cytology and sequencing of KRT4 and KRT13 genes) with the results of mucosal membrane biopsy, in order to evaluate the usefulness of non-invasive diagnostic tools.