title: Why are monozygotic twins different?
abstract: Although popularly designated as "identical", monozygotic (MZ) twins are rarely identical. Much has been speculated on the origin of MZ twins and several theories have been proposed. Post-fertilization events, such as chromosomal mosaicism, skewed X-inactivation and imprinting mechanisms, as well as other epigenetic mechanisms are responsible for the differences between MZ twins. Numerous discordant MZ twins have been reported including discordance for lateral asymmetry, major malformation, growth and intrauterine death of the co-twin. This discrepancy may have long-term implications on complex diseases and their predisposition, organ transplantation and interpretation of twin-based studies. We reviewed the genotypic and phenotypic differences between MZ twins and discuss their main causes.
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of S. Jo;atao, Medical Faculty of Porto, Porto, Portugal.
authors.forename: Sara
authors.initials: S
authors.lastname: Silva
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Martins
authors.forename: Alexandra
authors.initials: A
authors.lastname: Matias
authors.forename: Isaac
authors.initials: I
authors.lastname: Blickstein
mesh_terms: D000013:Congenital Abnormalities / Q000235:genetics; D044127:Epigenesis, Genetic; D005260:Female; D047109:Fetal Development / Q000235:genetics; D007839:Functional Laterality / Q000235:genetics; D005799:Genes, Dominant; D005808:Genes, Recessive; D056726:Genetic Association Studies; D018392:Genomic Imprinting; D006801:Humans; D008297:Male; D009030:Mosaicism; D009154:Mutation; D011247:Pregnancy; D038522:Twinning, Monozygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D049951:X Chromosome Inactivation / Q000235:genetics