title: Association between number of siblings and nervous system tumors suggests an infectious etiology.
abstract: OBJECTIVE
  To estimate the effect of the number of siblings on the risk of histopathologic subtypes of tumors of the nervous system using large population-based data.
  
  
  METHODS
  The Swedish Family-Cancer Database comprises 13,613 diagnoses of nervous system tumors with histopathologic information. We analyzed the data using Poisson regression models taking into account potential confounding effects of age, birth cohort, socioeconomic status, and family history of cancer.
  
  
  RESULTS
  The rate ratios (RR) for having four or more siblings vs none were significantly increased for hemangioblastoma (RR = 1.68), childhood neuroblastoma (RR = 2.01), and ependymoma (RR = 1.83, p trend < 0.01). For age at diagnosis < or =15 years, the RRs for individuals with three or more younger siblings compared to none were 1.34 for astrocytoma, 2.30 for medulloblastoma, 2.61 for ependymoma, 3.71 for meningioma, and 2.13 for neuroblastoma, with significant trends in risk. Non-significant decreased risks were found between the number of older siblings and nervous system tumors.
  
  
  CONCLUSIONS
  We provide the first reliable quantification of the effects of number of siblings on the risk of nervous system tumors. Sibship size and number of younger siblings correlate with the incidence of childhood nervous system tumors, suggesting a role of infectious agents in the etiology of the disease.
authors.affiliation: Deutsches Krebsforschungszentrum (DKFZ), Division of Molecular Genetic Epidemiology, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany. altieri73@gmail.com
authors.forename: Andrea
authors.initials: A
authors.lastname: Altieri
authors.forename: Felipe
authors.initials: F
authors.lastname: Castro
authors.forename: Justo Lorenzo
authors.initials: JL
authors.lastname: Bermejo
authors.forename: Kari
authors.initials: K
authors.lastname: Hemminki
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003141:Communicable Diseases / Q000453:epidemiology*; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009423:Nervous System Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D012042:Registries; D012307:Risk Factors; D035781:Siblings; D013548:Sweden