PharmVar updates for CYP3A4 star allele definitions

PharmVar announces several updates for CYP3A4 star allele definitions.

Retirement of the CYP3A4*1G allele: this allele was defined by a common variant in intron 10 (c.1026+12G>A) which was also found on many other haplotypes (or star alleles). PharmVar transiently designated the CYP3A4*1G allele as *36 due to a possible role of c.1025+12G>A being involved in the regulation of CYP3A4 expression. However, owing to the growing body of inconsistent findings regarding associations of c.1026+12G>A and higher or lower expression levels and/or CYP3A4 activity, PharmVar withdrew this redesignation in January 2023 (v5.2.17) which led to the retirement of the CYP3A4*36 (former *1G) allele. Per PharmVar rules, intronic variants are only utilized for star allele definitions if there is convincing evidence that the variant impacts protein function. Therefore, c.1026+12G>A was also removed from all other star allele definitions.

CYP3A4 gene regulation is complex and appears to be governed by a layer of processes, among them long noncoding RNAs, microRNAs and transcription factors which may also influence CYP3A5 activity. Furthermore, there is substrate overlap between CYP3A4 and CYP3A5 and thus, variation in the CYP3A5 gene, further complicates the characterization of CYP3A4 allele function. Investigators are encouraged to include c.1026+12G>A in their carefully designed investigations to produce conclusive evidence regarding the functional impact of c.1026+12G>A.

We would also like to highlight the addition of a novel star allele, CYP3A4*38 which is characterized by two variants which on their own define CYP3A4*3 and *11. Noteworthy, the CYP3A4*3-defining variant c.1334T>C (p.M445T) has also been found together with the intronic SNP defining CYP3A4*22; this allele was designated CYP3A4*37. Consequently, samples heterozygous for these SNPs could have CYP3A4*1/*37 or *3/*22 or *1/*38 or *3/*11 genotypes, respectively. Since the functional impact of c.1334T>C (p.M445T) remains elusive it is unknown whether alternate genotypes differ in function.

Lastly, the evidence level of several alleles has been updated from ‘Limited’ or ‘Moderate’ to ‘Definitive’ indicating that these alleles are now fully characterized.

These efforts were only possible by the dedicated work of the PharmVar Team and the CYP3A4 gene experts for volunteering their time and expertise.