Analysis of DNA tandem repeats in ALS from Whole Genome Sequencing: Role of FRA10Ac1 gene repeat expansion in ALS

The C9ORF72 gene repeat expansion is the most frequent cause of ALS. Long repeats alleles in ATXN-1, ATXN-2, and NIPA1 genes are associated to ALS susceptibility. Tandem Repeat Polymorphisms (TRPs) are good candidates for missing hereditability in ALS (40%), although they were never systematically analyzed as they represent a remarkable challenge to NGS. The aim of this study is to perform a systematic analysis of TRPs in ALS by combining NGS and novel bioinformatics tools. We performed our analysis from whole genome sequencing data (WGS) of 70 ALS cases. TRPs were evaluated by means of a software developed within our consortium to detect tandem repeat expansion. Validation of expanded loci was conducted by Repeat primer PCR We identified an ALS patient with a CGG expansion in 5'UTR of FRA10AC1 gene. To explore the possible role of this CGG expansion in ALS we screened a cohort of 337 ALS and 285 controls and we found 3 expanded patients (0.9%) and no control. We failed to replicated this result in a second cohort of 426 ALS patients and 733 controls (1 ALS (0.2%) and 5 controls (0.7%)) Overall, we observed the CGG expansion in 4/763 (0.5%) ALS patients and 5/1018 controls (0.5%). FRA10AC1 gene expression was not silenced by the expansion. The software we developed can detect epeat expansions from WGS data, although FRA10AC1 CGG expansion seems not to be involved in ALS pathogenesis. Conversely to what previously reported, large CGG expansion at this locus do not decrease gene expression