Pathogenicity analysis of small in-frame deletions in DMD/DMB patients: reaching certainty of uncertainty

LUCE, LEONELA; CARCIONE, MICAELA; MAZZANTI, CHIARA; BRUQUE, CARLOS DAVID ; GILIBERTO, FLORENCIA

CABA

Congreso; Reunión Conjunta de Sociedades de Biociencias(SAIC, SAIB, SAI, SAA, SAB, SAB, SAFE, SAFIS, SAH, SAP); 2017

Pathogenicity analysis of small in-frame deletions in DMD/DMB patients:reaching certainty of uncertaintyDuchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD) are X-linked genetic diseases caused by mutations in the DMD gene. DMD is a severe dystrophy that occurs due to absence of dystrophin and affects 1:3.500 born males, whereas BMD is less severe due to less expression or function of the protein and affects 1:18.000. Molecular alterations in DMD gene are gross deletions/duplications in 80% of cases and small mutations in 20%. Large rearrangements are identified by Multiplex Ligation-dependent Probe Amplification (MLPA), while point mutations are detected by gene sequencing. The ?reading frame theory? establishes a correlation between phenotype and mutation type, which agrees with the observed phenotype in 92% of cases. According to this theory, patients carrying a mutation causing a disruption on the translational reading frame (out-of-frame mutation) show a clinical progression to DMD, while patients with a genetic alteration that do not affect the translational reading frame (in-frame mutation) develop a milder phenotype, BMD-like.From a cohort of 175 patients with clinical diagnosis of DMD/BMD, analyzed by MLPA and 40 of them also studied by Next Generation Sequencing (Whole Exome Sequencing), we have detected two small in-frame variants c.10101_10103delAGA and c.120_131delCTTCAGTGACCT in two patients with a DMD phenotype. As the observed phenotype did not adjust to the ?reading frame theory? and there were none or scarce cases carrying these mutations previously reported, our aim was to increase the predicted pathogenic effect of these two mutations found. Two different strategies were implemented, an intrafamilial segregation analysis and a functional and structural bioinformatic analysis of the dystrophin protein. This work offers an example of different methodologies to corroborate the pathogenic effect of Variants of Unknown Significance (VUS), one of the major challenges of the Next Generation Sequencing data interpretation.