Desmin splice variants causing cardiac and skeletal myopathy

Desmin myopathy is a hereditary or sporadic cardiac and skeletal myopathy c haracterised by intracytoplasmic accumulation of desmin reactive deposits i n muscle cells. We have characterised novel splice site mutations in the ge ne desmin resulting in deletion of the entire exon 3 during the pre-mRNA sp licing. Sequencing of cDNA and genomic DNA identified a heterozygous de nov o A to G change at the +3 position of the splice donor site of intron 3 (IV S3+3A-->G) in a patient with sporadic skeletal and cardiac myopathy. A G to A transition at the highly conserved -1 nucleotide position of intron 2 af fecting the splice acceptor site (IVS2-1G-->A) was found in an unrelated pa tient with a similar phenotype. Expression of genomic DNA fragments carryin g the IVS3+3A-->G and IVS2-1G-->A mutations confirmed that these mutations cause exon 3 deletion. Aberrant splicing leads to an in frame deletion of 3 2 complete codons and is predicted to result in mutant desmin lacking 32 am ino acids from the 1B segment of the alpha helical rod. Functional analysis of the mutant desmin in SW13 (vim-) cells showed aggregation of abnormal c oarse clumps of desmin positive material dispersed throughout the cytoplasm . This is the first report on the pathogenic potentials of splice site muta tions in the desmin gene.