Figure 1.

Schematic representation of a compound heterozygous double hit. In the normal situation each gene on the autosomes is present in two copies (diploidy). In this example both horizontally dashed genes are present in only one copy (haploidy). In addition, the horizontally dashed gene on the right is affected by a coding single nucleotide variant (SNV). The compound heterozygous double hit consists of the co-occurrence of a CNV (in this example a deletion) on the one allele and a coding SNV on the remaining allele.