There are multiple types of genetic alterations that contribute to human variability, many of which have yet to be fully characterized or properly understood. This genetic variation can involve differences in the DNA nucleotide sequence as well as changes in chromosome structure. Single nucleotide polymorphisms (SNPs) are common variants of individual nucleotide sequence that are frequently observed in the population (>1%). CNVs are a type of structural variant involving alterations in the number of copies of specific regions of DNA, which can either be deleted or duplicated. These chromosomal deletions and duplications involve fairly large stretches of DNA (that is, thousands of nucleotides [>1 kb], which may span many different genes) but can range considerably in size as well as prevalence. As is the case for other types of genetic mutations, some CNVs are inherited whereas others spontaneously arise de novo. To date, most CNV research in psychiatry has focused on rare forms of copy number variation that occur with a frequency of <1%.
