AUTHOR=Botta Annalisa , Visconti Virginia Veronica , Fontana Luana , Bisceglia Paola , Bengala Mario , Massa Roberto , Bagni Ilaria , Cardani Rosanna , Sangiuolo Federica , Meola Giovanni , Antonini Giovanni , Petrucci Antonio , Pegoraro Elena , D’Apice Maria Rosaria , Novelli Giuseppe 

TITLE=A 14-Year Italian Experience in DM2 Genetic Testing: Frequency and Distribution of Normal and Premutated CNBP Alleles

JOURNAL=Frontiers in Genetics

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2021.668094

DOI=10.3389/fgene.2021.668094

ISSN=1664-8021

ABSTRACT=<p>Myotonic dystrophy type 2 (DM2) is a multisystemic disorder caused by a (CCTG)<sub><italic>n</italic></sub> in intron 1 of the <italic>CNBP</italic> gene. The CCTG repeat tract is part of a complex (TG)<sub><italic>v</italic></sub>(TCTG)<sub><italic>w</italic></sub>(CCTG)<sub><italic>x</italic></sub>(NCTG)<sub><italic>y</italic></sub>(CCTG)<sub><italic>z</italic></sub> motif generally interrupted in <italic>CNBP</italic> healthy range alleles. Here we report our 14-year experience of DM2 postnatal genetic testing in a total of 570 individuals. The DM2 locus has been analyzed by a combination of SR-PCR, TP-PCR, LR-PCR, and Sanger sequencing of <italic>CNBP</italic> alleles. DM2 molecular diagnosis has been confirmed in 187/570 samples analyzed (32.8%) and is mainly associated with the presence of myotonia in patients. This set of <italic>CNBP</italic> alleles showed unimodal distribution with 25 different alleles ranging from 108 to 168 bp, in accordance with previous studies on European populations. The most frequent <italic>CNBP</italic> alleles consisted of 138, 134, 140, and 136 bps with an overall locus heterozygosity of 90%. Sequencing of 103 unexpanded <italic>CNBP</italic> alleles in DM2-positive patients revealed that (CCTG)<sub>5</sub>(NCTG)<sub>3</sub>(CCTG)<sub>7</sub> and (CCTG)<sub>6</sub>(NCTG)<sub>3</sub>(CCTG)<sub>7</sub> are the most common interruption motifs. We also characterized five <italic>CNBP</italic> premutated alleles with (CCTG)<sub><italic>n</italic></sub> repetitions from <italic>n</italic> = 36 to <italic>n</italic> = 53. However, the molecular and clinical consequences in our cohort of samples are not unequivocal. Data that emerged from this study are representative of the Italian population and are useful tools for National and European centers offering DM2 genetic testing and counseling.</p>