Mutational spectrum of Chinese LGMD patients by targeted next-generation sequencing

Abstract

This study aimed to study the diagnostic value of targeted next-generation sequencing (NGS) in limb-girdle muscular dystrophies (LGMDs), and investigate the mutational spectrum of Chinese LGMD patients. We performed targeted NGS covering 420 genes in 180 patients who were consecutively suspected of LGMDs and underwent muscle biopsies from January 2013 to May 2015. The association between genotype and myopathological profiles was analyzed in the genetically confirmed LGMD patients. With targeted NGS, one or more rare variants were detected in 138 patients, of whom 113 had causative mutations, 10 sporadic patients had one pathogenic heterozygous mutation related to a recessive pattern of LGMDs, and 15 had variants of uncertain significance. No disease-causing mutation was found in the remaining 42 patients. Combined with the myopathological findings, we achieved a positive genetic diagnostic rate as 68.3% (123/180). Totally 105 patients were diagnosed as LGMDs with genetic basis. Among these 105 patients, the most common subtypes were LGMD2B in 52 (49.5%), LGMD2A in 26 (24.8%) and LGMD 2D in eight (7.6%), followed by LGMD1B in seven (6.7%), LGMD1E in four (3.8%), LGMD2I in three (2.9%), and LGMD2E, 2F, 2H, 2K, 2L in one patient (1.0%), respectively. Although some characteristic pathological changes may suggest certain LGMD subtypes, both heterogeneous findings in a certain subtype and overlapping presentations among different subtypes were not uncommon. The application of NGS, together with thorough clinical and myopathological evaluation, can substantially improve the molecular diagnostic rate in LGMDs. Confirming the genetic diagnosis in LGMD patients can help improve our understanding of their myopathological changes.

Fig 1. Flowchart of patients’ enrollment.

Fig 2. Overview of diagnoses of patients and spectrum of LGMD subtypes.

Fig 3. Myopathological changes of LGMD patients.

A. NADH-TR staining shows lobulated fibers (arrow) in a LGMD2B patient. B. MGT staining shows red-ragged fibers (arrow) in a LGMD2B patient. C. MGT staining shows nemaline bodies (arrow) in a LGMD2A patient. D. NADH-TR staining shows multi-minicores (arrow) in a LGMD2A patient. E. Immunohistochemical labelling of N-terminal dystrophin shows decreased or absent expression (asterisk) in a LGMD2A patient. F. Immunohistochemical labelling of dysferlin shows decreased expression (asterisk) in a LGMD2A patient. Abbreviations: LGMD = limb-girdle muscular dystrophy; NADH-TR = nicotinamide adenine dinucleotide-tetrazolium reductase; MGT = modified Gomori trichrome.