title: Influence of gender on susceptibility to multiple sclerosis and age of onset in concordant sibships.
abstract: BACKGROUND
  Research has produced conflicting findings about whether there is an excess of like-sexed pairs among concordant multiple sclerosis (MS) sibships. Although a positive correlation in onset age among sibling pairs overall has been reported, no data have been published describing age at onset correlations for like-sexed versus unlike-sexed pairs. The purpose of this study was to provide additional information on both issues.
  
  
  METHODS
  Patients with an MS sibling were sought through the files of the University of Alberta MS clinic (Edmonton, Canada). The clinic neurologist either reviewed clinical/autopsy material or assessed relatives of index cases prior to accepting the relative as having MS. Pairs of siblings (excluding twins) were divided into (1) male-male pairs, (2) female-female pairs, and (3) female-male pairs.
  
  
  RESULTS
  A total of 62 concordant sibling pairs were identified. There were 33 like-sexed pairs (6 male-male/27 female-female) and 29 unlike-sexed pairs. The observed number of like-sexed pairs was not significantly different from the expected frequency using 2 x 2 chi2 analysis, where expected values represent the binomial distribution predicted from the frequency of each sex as determined by total number of males and females. The age at onset intraclass correlation coefficient was -0.09 for sibling pairs overall, -0.22 for like-sexed pairs and +0.02 for unlike-sexed pairs.
  
  
  CONCLUSIONS
  This study does not provide evidence for an association between disease susceptibility and gender in siblings concordant for MS; nor does it suggest that genetics plays a role in onset age.
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, Edmonton.
authors.forename: S A
authors.initials: SA
authors.lastname: Warren
authors.forename: K G
authors.initials: KG
authors.lastname: Warren
mesh_terms: D017668:Age of Onset; D000416:Alberta / Q000453:epidemiology; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D004198:Disease Susceptibility; D005192:Family Health; D005260:Female; D006801:Humans; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology*; D012737:Sex Factors