The importance of molecular differential diagnosis of Muscular Dystrophies in the era of gene/mutation-dependent therapies: the dystrophinopathy model.

CARCIONE, MICAELA;; LEONELA LUCE; FLORENCIA GILIBERTO; MAZZANTI, CHIARA

Encuentro; FIRST GLOBAL SCIENTIFIC EXCHANGE MEETING (GSEM).; 2020

PTC Therapeutics

The importance of molecular differential diagnosis of Muscular Dystrophies in the era of gene/mutation-dependent therapies: the dystrophinopathy model. Luce, Leonela1,2; Carcione, Micaela1,2; Mazzanti, Chiara1,2; Giliberto, Florencia1,2.1.Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Cátedra de Genética, Laboratorio de Distrofinopatías. Buenos Aires, Argentina.2.CONICET - Universidad de Buenos Aires, Instituto de Inmunología, Genética y Metabolismo (INIGEM). Buenos Aires, Argentina.Background: Muscular Dystrophies (MD) are hereditary pathologies affecting skeletal muscle. Molecular diagnosis is crucial to differentiate them, giving overlapping clinical features. Dystrophinopathies are the most prevalent, caused by DMD mutations. Hitherto, 2 mutation-dependent protocols have conditional approval: Ataluren and Exon 51 skipping. Objective: Our aim was to provide differential molecular diagnosis in order to determine eligibility for these mutation-dependent therapies. Methods: We analysed 400 boys with clinical diagnosis of Dystrophinopathy, implementing an algorithm based on best practice guidelines. When no molecular alteration was identified in DMD, we broaden the screening to other MD genes. Furthermore, a thorough characterization of the nonsense was performed. Results: Dystrophinopathy clinical diagnosis was confirmed in 371 (92,8%) patients. After broadening mutational screening to genes linked to other MD, we reached the differential diagnosis in other 17 patients. Therefore, the strategy allowed determination of disease aetiology in 97% of boys. Regarding treatment, 23 patients resulted candidates for Exon Skipping of exon 51, 24 for exon 53 and 14 for exon 45, while another 70 were eligible for Ataluren. According to our results, the frequency of each type of DMD alterations was 56.6% gross deletions, 14.9% gross duplications, 25.4% small variants and 0.7% large del-dups. Respecting small sequence variant, they could be classified according to their effect: 42.6% nonsense, 32% frameshift, 20.5% splice site variants, 2.4% missense, 1.64% inframe and 0.82% synonym.Granted the existence of therapeutic protocols for nonsense, it is of utmost importance to deepen the knowledge of the effect of this type of alterations and their characterization. We have found 64 nonsense in non-related patients, distributed in 34/79 exons, mainly affecting rod domain (65.6%). These substitutions principally took place in first codon position (73%), followed by 19% affecting the second and 8% the third. Finally, stop codon generation rate was: TGA (46.9%), TAG (32,8%) and TAA (20.3%). Conclusions: Our molecular algorithm probed to be efficient for the achievement of differential diagnosis, playing a crucial role in patient management, standard-of-care and genetic counselling. Finally, this study contributes to the understanding of genetic/molecular basis of these pathologies, key information for development and improvement of mutation-dependent therapies.