The Basis of Diversity in Laminopathy Phenotypes Caused by Variants in the Intron 8 Donor Splice Site of the LMNA Gene

Laminopathies are a broad spectrum of hereditary diseases caused by pathogenic variants of the LMNA gene. Such phenotypic diversity is explained by the function of intermediate filaments encoded by the LMNA gene. We examined a family with an overlapping phenotype of cardiac arrhythmia, cardiomyopathy, limb-girdle muscular dystrophy, and partial lipodystrophy. The cause of the disorder was a novel LMNA(NM_170707.4):c.1488+2T>C variant. The analysis of mRNA extracted from the probands' blood showed a multitude of alternative splicing products, which was the cause of the complex phenotype in affected family members. Aside from that, we used minigene constructs to analyze the c.1488+2T>C variant, as well as other previously described variants affecting the same donor splice site in intron 8 (c.1488+1G>A, c.1488+5G>C, c.1488+5G>A). We demonstrated that these variants result in multiple splicing events, each producing splicing products with varying prevalence. Our experiments suggest that the variety of alternative transcripts contributes to complex phenotypes, while the quantitative ratio of these transcripts influences the varying severity of the disease.