title: Familial clustering of Hodgkin lymphoma and multiple sclerosis.
abstract: BACKGROUND
  Epidemiologic similarities between Hodgkin lymphoma in young adults (i.e., between 15 and 44 years old) and multiple sclerosis have led to the suggestion that these diseases may have related etiologies. Previous investigations have not supported this hypothesis, but the negative results could have been caused by methodologic problems. We therefore assessed the risk of developing Hodgkin lymphoma for patients with multiple sclerosis and for their families and the risk of developing multiple sclerosis for patients with Hodgkin lymphoma and for their families.
  
  
  METHODS
  We identified 11,790 patients with multiple sclerosis and 19,599 of their first-degree relatives in Danish population-based registers and followed them for the occurrence of Hodgkin lymphoma. Analogously, we identified 4381 patients with Hodgkin lymphoma and 7388 of their first-degree relatives and followed them for the occurrence of multiple sclerosis. The relative risks (RRs) of Hodgkin lymphoma and multiple sclerosis were expressed as standardized incidence ratios (i.e., the ratio between observed and expected numbers of outcomes based on age, sex, and period-specific incidence rates). All statistical tests were two-sided.
  
  
  RESULTS
  Overall, six cases of Hodgkin lymphoma were identified in patients with multiple sclerosis (RR for Hodgkin lymphoma = 1.40, 95% confidence interval [CI] = 0.63 to 3.12), two of which occurred in young adults (RR = 1.59, 95% CI = 0.40 to 6.37). The risk of young-adult-onset Hodgkin lymphoma was statistically significantly increased in the first-degree relatives of patients with multiple sclerosis (RR = 1.93, 95% CI = 1.01 to 3.71; n = 9 such lymphomas). Two cases of multiple sclerosis were identified among young adult patients with Hodgkin lymphoma (RR for multiple sclerosis = 0.82, 95% CI = 0.20 to 3.27), and the risk for multiple sclerosis was statistically significantly increased in their first-degree relatives (RR = 2.76, 95% CI = 1.44 to 5.31; n = 9 such multiple sclerosis cases).
  
  
  CONCLUSIONS
  The observed familial clustering of multiple sclerosis and young-adult-onset Hodgkin lymphoma is consistent with the hypothesis that the two conditions share environmental and/or constitutional etiologies.
authors.affiliation: Department of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark. hhj@ssi.dk
authors.forename: Henrik
authors.initials: H
authors.lastname: Hjalgrim
authors.forename: Søren
authors.initials: S
authors.lastname: Rasmussen
authors.forename: Klaus
authors.initials: K
authors.lastname: Rostgaard
authors.forename: Nete Munk
authors.initials: NM
authors.lastname: Nielsen
authors.forename: Nils
authors.initials: N
authors.lastname: Koch-Henriksen
authors.forename: Lars
authors.initials: L
authors.lastname: Munksgaard
authors.forename: Hans H
authors.initials: HH
authors.lastname: Storm
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001824:Body Constitution; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006689:Hodgkin Disease / Q000453:epidemiology* / Q000209:etiology* / Q000235:genetics / Q000276:immunology; D006801:Humans; D015994:Incidence; D008228:Lymphoma, Non-Hodgkin / Q000453:epidemiology / Q000209:etiology; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000209:etiology* / Q000235:genetics / Q000276:immunology; D016017:Odds Ratio; D012042:Registries; D018570:Risk Assessment; D013029:Space-Time Clustering