A novel ANO5 splicing variant in a LGMD2L patient leads to production of a truncated aggregation‐prone Ano5 peptide

Abstract

Mutations in ANO5 cause several human diseases including gnathodiaphyseal dysplasia 1 (GDD1), limb‐girdle muscular dystrophy 2L (LGMD2L), and Miyoshi myopathy 3 (MMD3). Previous work showed that complete genetic disruption of Ano5 in mice did not recapitulate human muscular dystrophy, while residual expression of mutant Ano5 in a gene trapped mouse developed muscular dystrophy with defective membrane repair. This suggests that truncated Ano5 expression may be pathogenic. Here, we screened a panel of commercial anti‐Ano5 antibodies using a recombinant adenovirus expressing human Ano5 with FLAG and YFP at the N‐ and C‐terminus, respectively. The monoclonal antibody (mAb) N421A/85 was found to specifically detect human Ano5 by immunoblotting and immunofluorescence staining. The antigen epitope was mapped to a region of 28 residues within the N‐terminus. Immunofluorescence staining of muscle cryosections from healthy control subjects showed that Ano5 is localized at the sarcoplasmic reticulum. The muscle biopsy from a LGMD2L patient homozygous for the c.191dupA mutation showed no Ano5 signal, confirming the specificity of the N421A/85 antibody. Surprisingly, strong Ano5 signal was detected in a patient with compound heterozygous mutations (c.191dupA and a novel splice donor site variant c.363 + 4A > G at the exon 6–intron 6 junction). Interestingly, insertion of the mutant intron 6, but not the wild‐type intron 6, into human ANO5 cDNA resulted in a major transcript that carried the first 158‐bp of intron 6. Transfection of the construct encoding the first 121 amino acids into C2C12 cells resulted in protein aggregate formation, suggesting that aggregate‐forming Ano5 peptide may contribute to the pathogenesis of muscular dystrophy.