Rs67666821

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.