FXN and fragile X syndrome: Within this dataset, we show the following: (1) WGS accurately classifies alleles in the normal, premutation and full-mutation range in all loci assessed except FMR1 (which causes fragile X syndrome) (Extended Data Fig. 3a and Supplementary Table 4); (2) the accuracy of repeat sizing by WGS is not affected by genetic ancestry by comparing genotypes generated by WGS with those generated by PCR from different populations (Extended Data Fig. 3b), but it might underestimate the size of large expansions in FMR1, DMPK, FXN and C9orf72, as previously described7.