CYP3A4 and pure red-cell aplasia: The CYP3A4*1B allele frequency has been shown in various studies to vary markedly between ethnic groups and match solely with the incidence of PRCa based on ethnicity (Walker et al, 1998; Ball et al, 1999; Paris et al, 1999; Sata et al, 2000; Tayeb et al, 2000; Kittles et al, 2002).