title: Infantile Hemangiomas in Twins: A Prospective Cohort Study.
abstract: BACKGROUND
  Twins have a higher-than-expected risk of infantile hemangiomas (IHs), but the exact reasons for this association are not clear. Comparing concordant and discordant twin pairs might help elucidate these factors and yield more information about IH risk factors.
  
  
  METHODS
  A prospective cohort study of twin pairs from 12 pediatric dermatology centers in the United States, Canada, Argentina, and Spain was conducted. Information regarding maternal pregnancy history, family history of vascular birthmarks, zygosity (if known), and pregnancy-related information was collected. Information regarding twins (N = 202 sets) included birthweight, gestational age (GA), presence or absence of IHs, numbers and subtypes of IHs, presence of other birthmarks, and other medical morbidities.
  
  
  RESULTS
  Two hundred two sets of twins were enrolled. Concordance for IH was present in 37% of twin pairs. Concordance for IH was inversely related to gestational age (GA), present in 42% of GA of 32 weeks or less, 36% of GA of 33 to 36 weeks, and 32% of GA of 37 weeks or more. Twins of GA of 34 weeks or less were more than two and a half times as likely to be concordant as those of GA of 35 weeks or more (odds ratio (OR) = 2.66, 95% confidence interval (CI) = 1.42-4.99; p < 0.01). In discordant twins, lower birthweight conferred a high risk of IH; of the 64 sets of twins with 10% or greater difference in weight, the smaller twin had IH in 62.5% (n = 40) of cases, versus 37.5% (n = 24) of cases in which the higher-birthweight twin was affected. Zygosity was reported in 188 twin sets (93%). Of these, 78% were dizygotic and 22% monozygotic. There was no statistically significant difference in rates of concordance between monozygotic twins (43%, 18/42) and dizygotic twins (36%, 52/146) (p = 0.50). In multivariate analysis comparing monozygotic and dizygotic twins, adjusting for effects of birthweight and sex, the likelihood of concordance for monozygotic was not appreciably higher than that for dizygotic twins (OR = 1.14, 95% CI = 0.52-2.49). Female sex also influenced concordance, confirming the effects of female sex on IH risk. The female-to-male ratio was 1.7:1 in the entire cohort and 1.9:1 in those with IH. Of the 61 concordant twin sets with known sex of both twins, 41% were female/female, 43% were female/male, and 16% were male/male.
  
  
  CONCLUSIONS
  These findings suggest that the origin of IHs is multifactorial and that predisposing factors such as birthweight, sex, and GA may interact with one another such that a threshold is reached for clinical expression.
authors: Division of Pediatric Dermatology, Department of Pediatrics, British Hospital of Buenos Aires, Buenos Aires, Argentina.
authors: M Fernanda
authors: MF
authors: Greco
authors: Department of Dermatology, School of Medicine, University of California at San Francisco, San Francisco, California.|Department of Pediatrics, School of Medicine, University of California at San Francisco, San Francisco, California.
authors: Ilona J
authors: IJ
authors: Frieden
authors: Department of Dermatology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors: Beth A
authors: BA
authors: Drolet
authors: Department of Dermatology, Columbia University, New York, New York.
authors: María C
authors: MC
authors: Garzon
authors: Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.|Department of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.
authors: Anthony J
authors: AJ
authors: Mancini
authors: Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.|Department of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.
authors: Sarah L
authors: SL
authors: Chamlin
authors: Department of Dermatology, Texas Children's Hospital, Baylor College of Medicine, Houston, Texas.
authors: Denise
authors: D
authors: Metry
authors: Division of Hematology and Oncology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
authors: Denise
authors: D
authors: Adams
authors: Division of Pediatric Dermatology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
authors: Anne
authors: A
authors: Lucky
authors: Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
authors: Mary Sue
authors: MS
authors: Wentzel
authors: Section of Dermatology, Children's Mercy Hospital and Clinics, Kansas City, Missouri.
authors: Kimberly A
authors: KA
authors: Horii
authors: Department of Dermatology, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain.
authors: Eulalia
authors: E
authors: Baselga
authors: Department of Pediatrics Dermatology, Dermatology Service, CHU, Sainte-Justine Hospital, Montreal, Quebec, Canada.
authors: Catherine C
authors: CC
authors: McCuaig
authors: Department of Pediatrics Dermatology, Dermatology Service, CHU, Sainte-Justine Hospital, Montreal, Quebec, Canada.
authors: Julie
authors: J
authors: Powell
authors: Department of Dermatology, School of Medicine, Indiana University, Indianapolis, Indiana.|Department of Pediatrics, School of Medicine, Indiana University, Indianapolis, Indiana.
authors: Anita
authors: A
authors: Haggstrom
authors: Department of Dermatology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors: Dawn
authors: D
authors: Siegel
authors: Department of Dermatology, Columbia University, New York, New York.
authors: Kimberly D
authors: KD
authors: Morel
authors: Division of Pediatric Dermatology, Hospital de Pediatria Prof. Dr. JP Garrahan, Buenos Aires, Argentina.
authors: M Rosa
authors: MR
authors: Cordisco
authors: Section of Dermatology, Children's Mercy Hospital and Clinics, Kansas City, Missouri.
authors: Amy J
authors: AJ
authors: Nopper
authors: Department of Dermatology, Oregon Health & Science University, Portland, Oregon.|Department of Pediatrics, Oregon Health & Science University, Portland, Oregon.
authors: Alfons
authors: A
authors: Krol
mesh_terms: D001724:Birth Weight; D015331:Cohort Studies; D004200:Diseases in Twins; D005260:Female; D005865:Gestational Age; D006391:Hemangioma / Q000235:genetics*; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011446:Prospective Studies; D012737:Sex Factors