title: X chromosome inactivation patterns correlate with fetal-placental anatomy in monozygotic twin pairs: implications for immune relatedness and concordance for autoimmunity.
abstract: BACKGROUND
  Monozygotic (MZ) twinning is a poorly understood phenomenon that may result in subtle biologic differences between twins, despite their identical inheritance. These differences may in part account for discordant expression of disease in MZ twin pairs. Due to their stochastic nature, differences in X chromosome inactivation patterns are one source of such variation in female MZ twins.
  
  
  METHODS
  We investigated X chromosome inactivation patterns in the blood of 41 MZ twin pairs based on methylation of the androgen receptor gene using a Hpa II-PCR assay. Twenty-six female MZ twin pairs with autoimmune disease (rheumatoid arthritis or multiple sclerosis) were studied. In addition, we studied 15 newborn female MZ twin pairs who were characterized at birth with respect to the anatomy of chorionic membranes (dichorionic versus monochorionic).
  
  
  RESULTS
  We found a strong correlation between dichorionic fetal anatomy and differences in X chromosome inactivation patterns between members of an MZ twin pair. In contrast, all monochorionic twin pairs had closely correlated patterns of X chromosome inactivation. X chromosome inactivation patterns did not distinguish between MZ twin pairs who were concordant or discordant for autoimmune disease.
  
  
  CONCLUSIONS
  The highly similar patterns of X chromosome inactivation among monochorionic twin pairs may result from their shared placental blood supply during intrauterine life. Alternatively, these patterns may indicate that X chromosome inactivation occurs before the twinning event in this anatomic subgroup of MZ twins. The data further suggest that these factors do not make a major contribution to the high discordance rates for autoimmune disease in MZ twin pairs.
authors.affiliation: Department of Medicine, North Shore University Hospital, Manhasset, New York 11030, USA.
authors.forename: V
authors.initials: V
authors.lastname: Trejo
authors.forename: C
authors.initials: C
authors.lastname: Derom
authors.forename: R
authors.initials: R
authors.lastname: Vlietinck
authors.forename: W
authors.initials: W
authors.lastname: Ollier
authors.forename: A
authors.initials: A
authors.lastname: Silman
authors.forename: G
authors.initials: G
authors.lastname: Ebers
authors.forename: R
authors.initials: R
authors.lastname: Derom
authors.forename: P K
authors.initials: PK
authors.lastname: Gregersen
mesh_terms: D001327:Autoimmune Diseases / Q000235:genetics*; D001483:Base Sequence; D019003:Deoxyribonuclease HpaII / Q000235:genetics; D004200:Diseases in Twins; D004303:Dosage Compensation, Genetic; D005260:Female; D005330:Fetofetal Transfusion; D014644:Genetic Variation; D006801:Humans; D007231:Infant, Newborn; D008969:Molecular Sequence Data; D010920:Placenta / Q000033:anatomy & histology / Q000098:blood supply; D016133:Polymerase Chain Reaction / Q000379:methods; D011247:Pregnancy; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D019003:Deoxyribonuclease HpaII