Molecular genetics in 4408 cardiomyopathy probands and 3008 relatives in Norway: 17 years of genetic testing in a national laboratory

To describe results from genetic testing for cardiomyopathies in a national laboratory for genetic testing in Norway since 2003. Retrospective data collection from the laboratory information management system at Unit for Cardiac and Cardiovascular Genetics, Oslo University hospital. Data from 4408 probands and 3008 relatives were available. Three probands had two variants, nine had incidental findings of variants not related to their cardiomyopathy diagnosis. Of the remaining 4396 probands, 65.1% were males, age at genetic testing was 50.9 (±18.1) years and 6.1% were under the age of 18. A likely pathogenic or pathogenic variant (216 different variants including 67 novel) was detected in 574 probands, corresponding to a hit-rate of genetic testing of 13.1% in total, 11.9% in hypertrophic, 14.1% in dilated, and 14.9% in arrhythmogenic right ventricular cardiomyopathy. Of the 3008 relatives, 47.6 % were males, age at genetic testing was 39.3 (±20.5) years, 17.9% were under the age of 18, and 43.2% were positive for the variant found in their family. Probands and relatives combined, 1/2809 persons in Norway were found to be heterozygous for a cardiomyopathy variant. Next Generation Sequencing provided more findings in dilated cardiomyopathy, especially in TTN accounting for 44.2% of all variants. Otherwise, the majority of variants were found in the classical sarcomeric and desmosomal genes. Genetic testing provided a genetic basis of the cardiomyopathy in 13.1% of probands, and subsequent family testing identified almost three times as many variant-positive relatives which could be offered preventive follow-up.