title: Study of undifferentiated spondyloarthropathy among first-degree relatives of ankylosing spondylitis probands.
abstract: OBJECTIVE
  To estimate in a Chinese population the prevalence of undifferentiated spondyloarthropathy (USpA) among first-degree relatives (FDRs) of ankylosing spondylitis (AS) probands, and to compare the clinical features of familial USpA with those of sporadic USpA.
  
  
  METHODS
  The FDRs of two separate cohorts of consecutive AS probands were evaluated for the prevalence of USpA, using the Modified New York criteria and the European Spondylitis Study Group criteria for AS and SpA, respectively. Sporadic USpA and FDRs of non-SpA rheumatic patient probands served as separate controls.
  
  
  RESULTS
  Among the 301 FDRs of 102 AS probands, 7.0% were USpA. This was 1000 times higher than the 147 FDRs of 40 non-SpA probands (P = 0.00230). Within the AS families, USpA was less male-dominated than AS (33.3 vs 72.5%) (P = 0.006). The only feature distinguishing familial from sporadic USpA was that the percentages of HLA B27 were 100 and 50%, respectively (P<0.001).
  
  
  CONCLUSIONS
  USpA and AS coexist in the same Chinese families, both being predisposed by HLA B27. In these families, a female gender favours the development of USpA rather than AS. A significant subset of sporadic USpA (HLA B27-negative group) has a different genetic predisposition compared with familial USpA.
authors.affiliation: Division of Allergy-Immunology-Rheumatology, Veterans General Hospital-Taipei, No. 201, Sec. 2, Shipai Road, Beitou Chiu, Taipei, Taiwan 112. ctchou@vghtpe.gov.tw
authors.forename: C T
authors.initials: CT
authors.lastname: Chou
authors.forename: K C
authors.initials: KC
authors.lastname: Lin
authors.forename: J C C
authors.initials: JC
authors.lastname: Wei
authors.forename: W C
authors.initials: WC
authors.lastname: Tsai
authors.forename: H H
authors.initials: HH
authors.lastname: Ho
authors.forename: C M
authors.initials: CM
authors.lastname: Hwang
authors.forename: J M
authors.initials: JM
authors.lastname: Cherng
authors.forename: C M
authors.initials: CM
authors.lastname: Hsu
authors.forename: D T Y
authors.initials: DT
authors.lastname: Yu
mesh_terms: D000328:Adult; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D020022:Genetic Predisposition to Disease; D015796:HLA-B27 Antigen / Q000032:analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D025242:Spondylarthropathies / Q000208:ethnology / Q000235:genetics*; D013167:Spondylitis, Ankylosing / Q000208:ethnology / Q000235:genetics
chemical_list: D015796:HLA-B27 Antigen