New genotype-phenotype correlations and transcriptomic findings in limb-girdle muscular dystrophy R9

We aimed to comprehensively investigate the clinical, genetic, muscle imaging, and pathological characteristics of limb-girdle muscular dystrophy R9 (LGMDR9) in a large cohort of Chinese patients. In addition, we sought to delineate the muscle transcriptomic landscape of LGMDR9 which has not been investigated.

In total, 44 genetically confirmed Chinese LGMDR9 patients were enrolled. They underwent a detailed clinical, imaging, and pathological assessment, followed by customized bioinformatics analyses of genome-wide transcriptome data.

LGMDR9 patients presented with heterogeneous clinical manifestations, including hyper-creatine kinase-emia without weakness (n = 15), as well as mild (n = 11), moderate (n = 7), and severe (n = 11) weakness subgroups determined by hierarchical analysis. Eleven of the 35 pathogenic FKRP variants identified in our cohort were novel, with the c.545A > G variant being the most common found in 72.7% (32/44) patients. Hierarchical analysis revealed that 15 patients harboring null variants (frameshift, nonsense, and large deletions) exhibited a more severe phenotype compared to those with missense/inframe variants in FKRP. Muscle biopsy showed a dystrophic pattern in 19 patients, necrotizing myopathy in 5 patients, and mild myopathic changes in 9 patients. Muscle magnetic resonance imaging analysis showed a concentric pattern of fatty infiltration in 60.7% (17/28) patients. Transcriptomic profiling of 12 muscle samples showed significant upregulation of genes related to inflammation/immune response and extracellular matrix remodeling (P < 0.05). Furthermore, weighted gene co-expression network analysis identified a "turquoise" module enriched in immune cell proliferation and inflammatory markers, which were strongly correlated with histopathological inflammatory scores validated by immunohistochemical staining.

Our findings indicate that null variants in FKRP may be associated with a severe phenotype. We also provide the first transcriptomic and experimental evidence of an immune-activated inflammatory microenvironment in LGMDR9 muscle tissue, which support the potential utility of immunomodulatory therapies in managing this condition.