Accurate and simple FXN-GAA repeats (Friedreich ataxia loci) estimation by long read targeted sequencing.

Abstract

Friedreich ataxia, an autosomal recessive disorder is caused by tandem GAA nucleotide repeats expansion in intron 1 of the FXN (frataxin gene). The GAA repeats above 66 in length are considered as pathogenic and commonly occurring repeats are 600-1200. Clinically the spectrum of the features is confined mainly to the neurological tissue, however, cardiomyopathy and diabetes mellitus has been observed in 60% and 30% of the subjects. The accurate detection of GAA repeats count is of utmost importance for clinical genetic correlation as no study has attempted an approach which is of high throughput nature and defines the sequence of GAA repeats. Largely, the method for detection of GAA repeats so far is either conventional PCR based screening and southern blot which is the gold standard method. We describe for the first time a method of long read sequencing wherein we utilized approach of long range targeted amplification of FXN-GAA repeats and sequencing on oxford MinION platform. We were able to achieve the successful amplification of GAA repeats ranging from 180-1200 at 250x coverage. The total throughput achievable for 96 samples can be less than 24 hours on one flow cell as per our protocol and is scalable and deployable at clinical day to sequencing.