ABCG2 and Thrombocytopenia: The identification of ABCG2 421C>A associated with severe thrombocytopenia is particularly of importance as the Asian population possess relatively high frequency of this variant, variant allele A frequency is 0.311 and 0.289 in Japanese and Han Chinese populations, respectively, as compared to other non-Asian populations, allele A frequency is only 0.117 in Caucasian population and non-polymorphic in African population according to the SNP database from NCBI (http://www.ncbi.nlm.nih.gov/SNP/snp_ref.cgi?rs=2231142).