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.

CYP4F2 is now fully curated by PharmVar

CYP4F2 contributes to the synthesis of cholesterol, steroids and other lipids. It has been shown to regulate the bioavailability of vitamin E and vitamin K, a co-factor that is critical to blood clotting. Variations in this important pharmacogene can affect vitamin K levels and thus, the dosing of vitamin K antagonists such as the widely used anticoagulant drug warfarin (CPIC level A and PharmGKB 1A evidence level) among others.

We are excited to announce that CYP4F2 is now fully curated by PharmVar and its gene page content reviewed by an international expert panel. Furthermore, the PharmVar Team has generated new data to provide a more comprehensive catalog of genetic variation of this gene. Not only have the two previously defined CYP4F2*2 and *3 now been fully characterized, several other novel haplotypes (or star alleles) have been identified and designated by PharmVar. Notably, the new and relatively commonly observed CYP4F2*4 allele has both sequence variants that otherwise define *2 (c.34T>G, W12G) and *3(c.1297G>A, V433M), respectively while the other three novel star alleles (CYP4F2*5, *6 and *7) are each characterized by a single amino acid change. Interestingly, CYP4F2*5 and *6 appear to be absent or rare in Asian populations; in contrast, *7 seems to be mostly present in African populations and their descendants. These new star alleles may contribute to unexplained variability in daily warfarin dosage requirements in non-White populations. We encourage the research and clinical communities to include this new knowledge in their investigations.