How SMRT sequencing can improve the prognosis and genetic counseling in DM1 patient
Abstract
Myotonic dystrophy type 1 (DM1) results from the expansion of an unstable CTG repeat that usually increases
across generations and over time in somatic tissues. CTG repeat instability and DM1 clinical manifestations
depend on the length of the repeat itself and the purity of the repeated sequence. The genetic counseling in
DM1 is very complex, due to the highly variable clinical presentation and technical difficulties in determining the
size and purity of the CTG expansion. We used PacBio Single Molecule Real-Time sequencing (SMRT) to
precisely measure large CTG repeat size and identify sequence interruptions of expanded allele to understand
clinical and genetic variability in DM1 patients. We sequenced several DM1 patients with CTG repeat
expansion ranging from 130 to > 1000 CTG repeats on the Sequel I and II systems from amplicons. We
obtained more than 77% full DM1 reads per sample, with >70% of the reads from expanded alleles. The data
includes long reads in the expected size range for all samples, including DM1 patients with more than 1000
CTG repeats. SMRT sequencing is very promising to sequence large triplet repeat expansions, to identify CTG
repeat interruptions and to estimate somatic mosaicism in DM1 patients. This method can significantly improve
the prognosis and counseling offered to patients.