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

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

doi:10.3389/fgene.2021.668094

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

Front Genet. 2021 Jun 21:12:668094. doi: 10.3389/fgene.2021.668094. eCollection 2021.

Authors

Annalisa Botta¹, Virginia Veronica Visconti¹, Luana Fontana¹, Paola Bisceglia^{2

3}, Mario Bengala², Roberto Massa⁴, Ilaria Bagni², Rosanna Cardani⁵, Federica Sangiuolo^{1

2}, Giovanni Meola^{6

7}, Giovanni Antonini⁸, Antonio Petrucci⁹, Elena Pegoraro¹⁰, Maria Rosaria D'Apice², Giuseppe Novelli^{1

2}

Affiliations

¹ Medical Genetics Section, Department of Biomedicine and Prevention, University of Rome Tor Vergata, Rome, Italy.
² Laboratory of Medical Genetics, Tor Vergata Hospital, Rome, Italy.
³ Research Laboratory, Complex Structure of Geriatrics, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy.
⁴ Neuromuscular Disease Unit, Department of Systems Medicine, University of Rome Tor Vergata, Rome, Italy.
⁵ BioCor Biobank, UOC SMEL-1 of Clinical Pathology, IRCCS-Policlinico San Donato, Milan, Italy.
⁶ Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.
⁷ Department of Neurorehabilitation Sciences, Casa di Cura del Policlinico, Milan, Italy.
⁸ Neuromuscular and Rare Disease Center, Department of Neuroscience, Mental Health and Sensory Organs (NESMOS), Sant'Andrea Hospital, Sapienza University of Rome, Rome, Italy.
⁹ Center for Neuromuscular and Neurological Rare Diseases, S. Camillo Forlanini Hospital, Rome, Italy.
¹⁰ Department of Neuroscience, University of Padua, Padua, Italy.

Abstract

Myotonic dystrophy type 2 (DM2) is a multisystemic disorder caused by a (CCTG) _n in intron 1 of the CNBP gene. The CCTG repeat tract is part of a complex (TG) _v (TCTG) _w (CCTG) _x (NCTG) _y (CCTG) _z motif generally interrupted in CNBP 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 CNBP 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 CNBP 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 CNBP alleles consisted of 138, 134, 140, and 136 bps with an overall locus heterozygosity of 90%. Sequencing of 103 unexpanded CNBP alleles in DM2-positive patients revealed that (CCTG)₅(NCTG)₃(CCTG)₇ and (CCTG)₆(NCTG)₃(CCTG)₇ are the most common interruption motifs. We also characterized five CNBP premutated alleles with (CCTG) _n repetitions from n = 36 to n = 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.

Keywords: CNBP premutations; DM2 genetic testing; alleles distribution; myotonic dystrophy type 2; penetrance.