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Genetic epidemiology of cystic fibrosis in Saguenay-Lac-St. Jean (Quebec, Canada). Daigneault J, Aubin G, Simard F, DeBraekeleer M Clinical Genetics April 1991 Presented by Soodtida Tangpraphaphorn. Introduction. Descriptive case-control genetic epidemiological study

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genetic epidemiology of cystic fibrosis in saguenay lac st jean quebec canada

Genetic epidemiology of cystic fibrosis in Saguenay-Lac-St. Jean (Quebec, Canada)

Daigneault J, Aubin G, Simard F,

DeBraekeleer M

Clinical Genetics April 1991

Presented by Soodtida Tangpraphaphorn

introduction
Introduction
  • Descriptive case-control genetic epidemiological study
    • Quantifies incidence, prevalence, carrier rates
    • Some EO associations, no causality established
      • Makes etiological hypotheses, suggests associations and causal relationships for future study
  • Study population shows elevated prevalence of CF compared to overall population at risk.
  • Inbreeding slightly higher in CF group compared to controls due to remote consanguinity.
  • Endogamy not higher in CF group than controls.
clinical cystic fibrosis
Clinical Cystic Fibrosis
  • Genetic respiratory illness with pleiotropy
    • Most commonly affects populations of NW European descent
    • Causes airway mucus to thicken, resulting in chronic respiratory obstruction and infections
    • Impairs pancreatic exocrine function
    • Complications can decrease lifespan
    • Diagnosed by sweat test
cellular cystic fibrosis
Cellular Cystic Fibrosis
  • Caused by mutation in CFTR gene
    • Most commonly DF508
  • Mutation results in defective protein product
    • Protein is a cell membrane ion channel
      • Defective protein affects chloride anion transport in/out of cell
        • Ion channel fails to export to cell membrane
        • Ion channel is in cell membrane, but cannot function
saguenay lac st jean
Saguenay-Lac-St.Jean
  • 200km NE of Quebec City
  • Inlet of St. Lawrence Seaway
  • Very geographically remote
  • Southernmost fjord in the world
study population
Study Population
  • Pop. 285,100 (1986); 98% French-speaking Catholics
  • Isolation
    • Settled in 1840s, migrated from Charlevoix
    • Founder effects
      • Mutation frequencies different from urban Canadian population
  • Particularly interesting to geneticists
    • Elevated carrier rates and prevalence of many different genetic disorders
study population10
Study Population
  • 127 CF cases in SLSJ
    • 125 patients from CF clinic at Chicoutimi, 2 from Quebec City
  • 3 groups population-based controls
    • Not described in this study
      • Requires readers to refer to investigators’ other studies
methods
Methods
  • Study time-frame (1975-1988)
  • Extract demographic information from database of CF cases in SLSJ
  • Migration histories from subjects and their families
  • Calculate prevalence & incidence from birth statistics and case data
  • Estimate carrier rate via Hardy-Weinberg equation
results
Results
  • Number of CF live births = 78
  • Total live births = 70351
  • CF incidence (#cases/#at risk) = 1 per 902
    • Incidence for all Canadian whites = 1 per 2500
    • Secular trends show stable annual IR
  • Hardy-Weinberg carrier rate = 1 per 15
  • Stronger kinship and more inbreeding in CF group
discussion
Discussion
  • SLSJ population not isolated for long periods of time
    • High prevalence may be attributable to mutations before migration from Charlevoix
    • Migration of large founder group brought many alleles into population
  • Different frequency of mutations
  • Good descriptive epidemiology
    • Study stands alone well, better when taken in context
prevention recommendations
Prevention Recommendations
  • Primary – increase genetic diversity by mating outside of population
  • Secondary – screen locals for genetic mutations and offer genetic counseling with family planning, incl. PGD
  • Tertiary – early detection in infants, more social-medical services, close medical supervision
references
References
  • Daigneault J, Aubin G, Simard F, DeBraekeleer M. Genetic epidemiology of cystic fibrosis in Saguenay-Lac-St. Jean (Quebec, Canada). Clinical Genetics. 1991;40:298-303.
  • Rozen R, DeBraekeleer M, Daigneault J, Ferreira-Rajabi L, Gerdes M, Lamoureaux L, Aubin G, Simard F, Fujiwara TM, Morgan K. Cystic fibrosis mutations in French Canadians: three CFTR mutations are relatively frequent in a Quebec population with an elevated incidence of cystic fibrosis. American Journal of Medical Genetics. 1992;42:360-364.
  • DeBraekeleer M, Daigneault J. Spatial distribution of the DF508 mutation in cystic fibrosis. Human Biology. 1992;64:167-174.
  • Daigneault J, Aubin G, Simard F, DeBraekeleer M. Incidence of cystic fibrosis in Saguenay-Lac-St. Jean (Quebec, Canada). Human Biology. 1992;64:115-119.