Predominance of Dystrophinopathy Genotypes in Mexican Male Patients Presenting as Muscular Dystrophy with A Normal Multiplex Polymerase Chain Reaction DMD Gene Result: A Study Including Targeted Next-Generation Sequencing

Abstract

The complete mutational spectrum of dystrophinopathies and limb-girdle muscular dystrophy (LGMD) remains unknown in Mexican population. Seventy-two unrelated Mexican male patients (73% of pediatric age) with clinical suspicion of muscular dystrophy and no evidence of DMD gene deletion on multiplex polymerase chain reaction (mPCR) analysis were analyzed by multiplex ligation-dependent probe amplification (MLPA). Those with a normal result were subjected to Sanger sequencing or to next-generation sequencing for DMD plus 10 selected LGMD-related genes. We achieved a diagnostic genotype in 80.5% (n = 58/72) of patients with predominance of dystrophinopathy-linked genotypes (68%, n = 49/72), followed by autosomal recessive LGMD-related genotypes (types 2A-R1, 2C-R5, 2E-R4, 2D-R3 and 2I-R9; 12.5%, n = 9/72). MLPA showed 4.2% of false-negatives for DMD deletions assessed by mPCR. Among the small DMD variants, 96.5% (n = 28/29) corresponded to null-alleles, most of which (72%) were inherited through a carrier mother. The FKRP p.[Leu276Ile]; [Asn463Asp] genotype is reported for the first time in Mexican patients as being associated with dilated cardiomyopathy. Absence of dysferlinopathies could be related to the small sample size and/or the predominantly pediatric age of patients. The employed strategy seems to be an affordable diagnosis approach for Mexican muscular dystrophy male patients and their families.

Keywords: Duchenne/Becker muscular dystrophies; Mexican population; dilated cardiomyopathy; limb-girdle muscular dystrophies; neuromuscular disorders; next-generation sequencing.

Figure 1

Flow diagram depicting the dystrophinopathy (DMD/BMD) and limb-girdle muscular dystrophy (LGMD) genotypes identified along the different stages of the present study. LGMD2A, 2C, 2E, 2D and 2I, now officially are LGMD R1, R5, R4, R3 and R9 respectively, and according to the LGMD classification proposed by the European Neuromuscular Centre (ENMC) [1]. Abbreviations: MLPA: multiplex ligation-dependent probe amplification; NGS: next-generation sequencing; SS: Sanger sequencing.