title: Cancer incidence in patients with polyglutamine diseases: a population-based study in Sweden.
abstract: BACKGROUND
  Polyglutamine (polyQ) diseases are characterised by the expansion of CAG triplet repeats in specific genes. The accumulated encoded proteins affect the transcription of numerous transcription factors. We investigated whether polyQ diseases reduce the risk of cancer development.
  
  
  METHODS
  Data on patients with the polyQ diseases Huntington's disease (HD), spinobulbar muscular atrophy (SBMA), and hereditary ataxia (HA) in Sweden were linked to the Swedish Cancer Registry. We calculated standardised incidence ratios for cancers at specific sites or of specific types and the risks were compared with those in the general population. We also analysed risks in the unaffected parents of patients.
  
  
  RESULTS
  In the period January, 1969, to December, 2008, we identified 1510 patients with HD, 471 with SBMA, and 3425 with HA. Cancer was diagnosed in 91 (6·0%) HD patients, 34 (7·2%) SBMA patients, and 421 (12·3%) HA patients. The standardised incidence ratios were 0·47 (95% CI 0·38-0·58), 0·65 (0·45-0·91), and 0·77 (0·70-0·85), respectively. Before diagnosis of polyQ disease, the risk of cancer was even lower. Cancer incidence and risk in the unaffected parents of patients with polyQ diseases were similar to those in the general population.
  
  
  CONCLUSIONS
  The consistently decreased incidence of cancer in patients with polyQ diseases suggests that a common mechanism protects against the development of cancer. This feature could be related to the polyQ-tract expansion seen in these diseases. Further studies are warranted to investigate the underlying mechanisms linking cancer and polyQ diseases.
  
  
  BACKGROUND
  Swedish Cancer Society, Swedish Council for Working Life and Social Research.
authors.affiliation: Centre for Primary Health Care Research, Lund University and Region Skåne, Lund, Sweden. Jianguang.ji@med.lu.se
authors.forename: Jianguang
authors.initials: J
authors.lastname: Ji
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
authors.forename: Jan
authors.initials: J
authors.lastname: Sundquist
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D016208:Databases, Factual; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology* / Q000235:genetics* / Q000503:physiopathology; D019636:Neurodegenerative Diseases / Q000453:epidemiology* / Q000235:genetics* / Q000503:physiopathology; D010455:Peptides / Q000235:genetics* / Q000378:metabolism; D012042:Registries; D012189:Retrospective Studies; D018570:Risk Assessment; D017678:Sex Distribution; D016019:Survival Analysis; D013548:Sweden / Q000453:epidemiology
chemical_list: D010455:Peptides; C097188:polyglutamine