LOH and copy-neutral LOH and their consequences for the pathogenesis of malignant myeloid disorders. SNP-As facilitate detection of LOH. Two types of LOH are depicted using chromosome 7 as an example. SNP karyograms demonstrate monosomy-7 on the right and UPD7q on the left. In the bottom portion, theoretic pathogenetic pathways resulting in LOH due to deletion or UPD are shown. UPD can result in duplication of a somatic activating mutation, acquired homozygosity of a germ line–encoded polymorphism occurring normally in heterozygous form, or duplication of maternal or paternal methylation pattern with either activation or total inactivation of the duplicated allele. In deletion, the remaining allele may harbor a somatic inactivating mutation, leading to hemizygosity of a germ-line polymorphism that carries functional consequences or haploinsufficiency.