Any Deletion, Insertion, duplication, or other variant in the DNA sequence of a Genome that results in that sequence being present in greater or lesser numbers relative to those seen in a normal, reference genome. A CNV can result from relatively simple duplications, either tandem or inverted, or deletion of small or large blocks of sequence. They might also be more complex, involving gains or losses of homologous sequences at multiple sites in the genome. Disruption of contiguous Gene sequences and altered gene dosages by CNVs have been shown to influence gene Expression, increase phenotypic variation and cause disease.