title: Affected twins in the familial intracranial aneurysm study.
abstract: OBJECTIVE
  Very few cases of intracranial aneurysms (IAs) in twins have been reported. Previous work has suggested that vulnerability to IA formation is heritable. Twin studies provide an opportunity to evaluate the impact of genetics on IA characteristics, including IA location. We therefore sought to examine IA location concordance, multiplicity, and rupture status within affected twin-pairs.
  
  
  METHODS
  The Familial Intracranial Aneurysm study was a multicenter study whose goal was to identify genetic and other risk factors for formation and rupture of IAs. The study required at least three affected family members or an affected sibling pair for inclusion. Subjects with fusiform aneurysms, an IA associated with an AVM, or a family history of conditions known to predispose to IA formation, such as polycystic kidney disease, Ehlers-Danlos syndrome, Marfan syndrome, fibromuscular dysplasia, or moyamoya syndrome were excluded. Twin-pairs were identified by birth date and were classified as monozygotic (MZ) or dizygotic (DZ) through DNA marker genotypes. In addition to zygosity, we evaluated twin-pairs by smoking status, major arterial territory of IAs, and rupture status. Location concordance was defined as the presence of an IA in the same arterial distribution (ICA, MCA, ACA, and vertebrobasilar), irrespective of laterality, in both members of a twin-pair. The Fisher exact test was used for comparisons between MZ and DZ twin-pairs.
  
  
  RESULTS
  A total of 16 affected twin-pairs were identified. Location concordance was observed in 8 of 11 MZ twin-pairs but in only 1 of 5 DZ twin-pairs (p = 0.08). Three MZ subjects had unknown IA locations and comprised the three instances of MZ discordance. Six of the 11 MZ twin-pairs and none of the 5 DZ twin-pairs had IAs in the ICA distribution (p = 0.03). Multiple IAs were observed in 11 of 22 MZ and 5 of 10 DZ twin-pairs. Thirteen (13) of the 32 subjects had an IA rupture, including 10 of 22 MZ twins.
  
  
  CONCLUSIONS
  We found that arterial location concordance was greater in MZ than DZ twins, which suggests a genetic influence upon aneurysm location. The 16 twin-pairs in the present study are nearly the total of affected twin-pairs that have been reported in the literature to date. Further studies are needed to determine the impact of genetics in the formation and rupture of IAs.
authors.affiliation: Department of Neurology, Indiana University, Indianapolis, Ind., USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Mackey
authors.forename: Robert D
authors.initials: RD
authors.lastname: Brown
authors.forename: Laura
authors.initials: L
authors.lastname: Sauerbeck
authors.forename: Richard
authors.initials: R
authors.lastname: Hornung
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Moomaw
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Koller
authors.forename: Tatiana
authors.initials: T
authors.lastname: Foroud
authors.forename: Ranjan
authors.initials: R
authors.lastname: Deka
authors.forename: Daniel
authors.initials: D
authors.lastname: Woo
authors.forename: Dawn
authors.initials: D
authors.lastname: Kleindorfer
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Flaherty
authors.forename: Irene
authors.initials: I
authors.lastname: Meissner
authors.forename: Craig
authors.initials: C
authors.lastname: Anderson
authors.forename: Guy
authors.initials: G
authors.lastname: Rouleau
authors.forename: E Sander
authors.initials: ES
authors.lastname: Connolly
authors.forename: John
authors.initials: J
authors.lastname: Huston
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Broderick
mesh_terms: D000328:Adult; D000368:Aged; D017542:Aneurysm, Ruptured / Q000235:genetics*; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000235:genetics* / Q000473:pathology; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D012422:Rupture, Spontaneous; D012907:Smoking; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult