rs67666821

A SNP in the CYP3A4 gene on chromosome 7. Its most notable genotype is T;T: CYP3A4*20 homozygote; side effects likely from many drugs

Gene
CYP3A4
Location
Chr 799,758,183 (GRCh38)
Highest magnitude
5.0Very important
Tested on
23andMe, AncestryDNA

Genotypes

As shown in 23andMe and AncestryDNA files.

  1. -;-Goodcommon in complete genomicsTypical · 0.0
  2. -;TNot ratedCYP3A4*20 carrier; potential side effects from certain drugsWorth knowing · 2.5
  3. T;TMost notableBadCYP3A4*20 homozygote; side effects likely from many drugsVery important · 5.0

On SNPedia: (-;-), (-;T), (T;T). Magnitude rates how notable a genotype is from 0 to 10, not how risky it is.

Conditions, medicines and genes

Other CYP3A4 SNPs

All CYP3A4 SNPs

Notes

From SNPedia

Notes

rs67666821 is a SNP describing the CYP3A4*20 allele. The normal/common form for this SNP is actually the null (ie deleted) form; the very rare (< 0.06% frequency in Caucasians) form encoding a nonfunctional CYP3A4 protein has a T (in dbSNP orientation) at this location. As of 2006, it was the only CYP3A4 SNP with a known functional consequence.. Carriers of one rs67666821(T) allele have an intermediate CYP3A4 metabolizer phenotype, and might be susceptible to side effects during drug therapy with substrates or inhibitors of CYP3A4 such as acetaminophen, codeine, cyclosporin A, diazepam and erythromycin.

Source and license

Adapted from rs67666821 on SNPedia, using a snapshot taken October 16, 2026. SNPedia content is shared under CC BY-NC-SA 3.0 US, and this page is shared under the same license.

SNPedia is a community-edited wiki. Its entries can be incomplete, out of date or wrong, and nothing here is a diagnosis or medical advice. Magnitude is a community rating of how interesting a genotype is, not a risk score.