Prevalence of weak D phenotypes in the general population of Québec, Canada: A focus on weak D type 42.

BACKGROUND AND OBJECTIVES: Weak D type 42 accounts for an unusually high proportion of weak D phenotypes in Québec (Canada), which contrasts with other predominantly White populations. However, its prevalence in the general population is unknown. We estimated the prevalence of weak D type 42 and other common weak D phenotypes in Québec. MATERIALS AND METHODS: We screened for RHD*01W.42 alleles among 1000 individuals of CARTaGENE-a cohort representative of Québec's population. The prevalence of weak D type 42 was calculated based on the allele frequency of RHD*01W.42 and d (i.e., all recessive alleles that confer a D- phenotype), assuming a Hardy-Weinberg equilibrium. This prevalence was then leveraged to calculate that of other common weak D phenotypes, using published prevalence estimates among weak D phenotypes. RESULTS: Two individuals harboured the RHD*01W.42/RHD*01 heterozygous genotype. Assuming an allele frequency of 38.19% for d, the overall prevalence of weak D type 42 was 0.08%. The following prevalence estimates were also obtained: 0.44% for all weak D phenotypes and 0.07%, 0.01% and 0.04% for weak D types 1, 2 and 3, respectively. CONCLUSION: Québec has the highest documented prevalence of weak D type 42, which was estimated at 0.08%.