Targeted next-generation sequencing reveals further genetic heterogeneity in axonal Charcot-Marie-Tooth neuropathy and a mutation in HSPB1

Charcot-Marie-Tooth disease (CMT) is a group of hereditary peripheral neuropathies. The dominantly inherited axonal CMT2 displays striking genetic heterogeneity, with 17 presently known disease genes. The large number of candidate genes, combined with lack of genotype-phenotype correlations, has made genetic diagnosis in CMT2 time-consuming and costly. In Finland, 25% of dominant CMT2 is explained by either a GDAP1 founder mutation or private MFN2 mutations but the rest of the families have remained without molecular diagnosis. Whole-exome and genome sequencing are powerful techniques to find disease mutations for CMT patients but they require large amounts of sequencing to confidently exclude heterozygous variants in all candidate genes, and they generate a vast amount of irrelevant data for diagnostic needs. Here we tested a targeted nextgeneration sequencing approach to screen the CMT2 genes. In total, 15 unrelated patients from dominant CMT2 families from Finland, in whom MFN2 and GDAP1 mutations had been excluded, participated in the study. The targeted approach produced sufficient sequence coverage for 95% of the 309 targeted exons, the rest we excluded by Sanger sequencing. Unexpectedly, the screen revealed a disease mutation only in one family, in the HSPB1 gene. Thus, new disease genes underlie CMT2 in the remaining families, indicating further genetic heterogeneity. We conclude that targeted next-generation sequencing is an efficient tool for genetic screening in CMT2 that also aids in the selection of patients for genome-wide approaches.