Pathogenic actions of LOH, both CN-LOH and deletion. CN-LOH can lead to the duplication of a disease-linked minor germline variant (top line, left) or an acquired mutation (top line, right). It can also lead to increased gene expression by the loss of a negative epigenetic mark (second line, left) or decreased gene expression by the duplication of a repressive epigenetic mark (second line, right). Deletion of chromosomal material can lead to the unveiling of a minor germline variant (third line, left) of acquired mutation (third line, right), resulting in hemizygosity. Furthermore, deletion can affect gene expression: it can lead to increased expression through loss of an imprinted allele, repression by loss of the expressed allele, or haploinsufficiency.