Individual patients have been reported (PMID 38129972) to carry only one of the two SNPs in the HapB3 haplotype (i.e., c.1236G>A without c.1129-5923C>G), suggesting that the two variants are not in complete linkage disequilibrium. CPIC updated the allele definition to include the c.1129-5923C>G SNP separately as this is likely the causal variant leading to decreased function. CPIC also retained the HapB3 haplotype definition for cases where only the c.1236G>A variant is tested (e.g. whole exome sequencing). While CPIC recommends to directly test the causal SNP if possible, in cases where only c.1236G>A is tested or results are available for, it should be clearly stated in the test report that "decreased function" was inferred by detecting the exonic tag SNP, and disclose that in rare cases, the causal decreased function variant c.1129-5923C>G may not be present despite having this tag SNP.