Background - Childhood-onset cardiomyopathy (CMP) is a heterogenous group of conditions the etiology of which is largely unknown. The influence of consanguinity on the genetics of CMP has not been addressed at a large scale. Methods - To unravel the genetic etiology of childhood-onset CMP in a consanguineous population a categorized approach was adopted. Cases with childhood-onset CMP were consecutively recruited. Based on the likelihood of founder mutation and on the clinical diagnosis, genetic test was categorized to either: (i) Targeted Genetic Test (TGT) with: targeted mutation test, single gene test, or multi-gene panel for Noonan syndrome, or (ii) Untargeted genetic test with whole exome sequencing (WES) or whole genome sequencing (WGS). Several bioinformatics tools were used to filter the variants. Results - 205 unrelated probands with various forms of CMP were evaluated. The median age of presentation was 10 months. In 30.2% (n=62), TGT had a yield of 82.7% compared to 33.6% for WES/WGS (n=143) giving an overall yield of 53.7%. Strikingly, 96.4% of the variants were homozygous, 9% of which were found in 4 dominant genes. Homozygous variants were also detected in 7 novel candidates ( ACACB , AASDH , CASZ1 , FLII , RHBDF1 , RPL3L , ULK1 ). Conclusions - Our work demonstrates the impact of consanguinity on the genetics of childhood-onset CMP, the value of adopting a categorized population-sensitive genetic approach, and the opportunity of uncovering novel genes. Our data suggest that if a founder mutation is not suspected, adopting WES/WGS as a first-line test should be considered.

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