CYP3A5*3 — tacrolimus and other CYP3A5 substrates
One copy of the CYP3A5*3 non-functional allele detected.
You have one working copy and one non-working copy of the CYP3A5 gene.
Intermediate CYP3A5 activity. Modestly slower clearance of tacrolimus (post-transplant immunosuppressant) and a few other drugs.
Your body clears the transplant medicine tacrolimus a bit more slowly than average — useful information if you ever need an organ transplant.
What this means
Most people of European descent are CYP3A5 non-expressers (two *3 alleles). Most people of African descent express functional CYP3A5 and need higher tacrolimus doses to reach therapeutic levels. Pre-transplant CYP3A5 genotyping shortens time-to-therapeutic-trough and is gaining traction in transplant centres.
CYP3A5 is an enzyme involved in clearing the transplant medicine tacrolimus from your blood. Interestingly, most people of European descent don't actually produce a working version of this enzyme — they carry two non-working copies. Most people of African descent do produce it, and as a result need higher tacrolimus doses to keep the same level in their blood. Checking this gene before a transplant helps doctors pick the right starting dose faster, and the practice is becoming more common at transplant centres. Outside the transplant setting, this information isn't usually relevant.
Caveats
- Relevant primarily if tacrolimus is prescribed (transplantation, some autoimmune protocols).
- Therapeutic drug monitoring (trough levels) remains essential regardless of genotype.
- For most healthy adults, this is purely informational.