What HLA-B*15:02 Means in Your 23andMe Raw Data

# What HLA-B*15:02 Means in Your 23andMe Raw Data

HLA-B15:02 is not a disease. It is a specific protein version made by the HLA-B gene, one of the immune system's ID tags. In a 23andMe raw file you do not see HLA-B15:02 typed directly. You see marker SNPs nearby, and some tools use those markers to guess whether you carry it. That guess matters because HLA-B*15:02 sharply raises the risk of serious skin reactions to carbamazepine. But a raw-file tag is not the same as a clinical test.

What does HLA-B*15:02 mean in my 23andMe raw data?

Your raw file is a long list of rsIDs, positions and genotypes. The HLA-B gene sits in a dense part of chromosome 6 where many immune genes are packed together. Consumer genotyping chips do not read the whole HLA-B gene. They probe selected single-letter markers, some of which sit near the gene. A third-party report may show HLA-B15:02 because one of those markers carries an allele that often travels with HLA-B15:02 in certain populations.

That is a tag SNP approach. It works statistically, not personally. A tag that tracks the allele well in Han Chinese samples may be much less useful in someone of European, African or another Asian ancestry. A missing tag does not rule out HLA-B*15:02. A present tag does not prove the allele is there.

A 23andMe raw-file tag is a population-level hint, not an HLA type. Do not stop or change carbamazepine because of a raw-file marker alone.

What HLA-B*15:02 actually is

HLA-B is a protein that sits on the surface of most cells and shows small pieces of the cell's interior to immune cells. That is how the immune system checks whether a cell is infected or abnormal. HLA-B*15:02 differs from other HLA-B versions by a few amino acids in the groove that holds those pieces.

Carbamazepine or one of its breakdown products fits into this altered groove. In a carrier, T cells can see that drug-protein combination as foreign and attack the skin and mucous membranes. The result is Stevens-Johnson syndrome or toxic epidermal necrolysis, two severe skin reactions that can cause large areas of skin to peel away and can be fatal. One copy of HLA-B*15:02 is enough for the risk to apply.

The allele itself is not a disease. Many carriers never take carbamazepine and never have a reaction.

Why carbamazepine is the main drug concern

Carbamazepine is used for epilepsy, trigeminal neuralgia and bipolar disorder. The risk of Stevens-Johnson syndrome is highest in the first 2 to 8 weeks of treatment. It is not driven by dose in a simple way. A reaction can start with fever, sore throat, mouth ulcers, red eyes or a spreading rash, and it needs urgent medical attention. Phenytoin carries similar warnings in some places, but carbamazepine has the strongest evidence.

HLA-B*15:02 is most common in East, Southeast and South Asian populations, and much rarer in Europe and sub-Saharan Africa. In some Han Chinese and Thai groups the frequency is 5 to 15 percent. In most European groups it is below 0.5 percent.

This is why many health systems screen for HLA-B*15:02 before prescribing carbamazepine to people with ancestry from at-risk regions. The test they use is not a consumer chip.

What you actually see in a raw file

In a 23andMe browser you do not see 'HLA-B15:02' in the raw data. You see rows for nearby markers on chromosome 6, each with a genotype like C/T. A report may interpret one of those alleles as a tag for HLA-B15:02 because that allele is more common in carriers from some East Asian reference groups. Another person's file may have no row for one of those markers at all, depending on the chip version.

23andMe v3, v4 and v5 use different marker sets. Third-party tools sometimes impute from whichever nearby markers are available. That can change a call between chips or between reference panels. It is also why the same person can get a different HLA-B*15:02 guess from two different raw-file services. The raw file also does not tell you whether you carry one or two copies of the actual allele.

The obvious follow-up: should you avoid carbamazepine?

If a raw-file tool flags HLA-B15:02 and you are about to start carbamazepine, take the flag seriously enough to ask for the right test. A clinical HLA-B15:02 test sequences or probes the actual allele and is the result that should guide the prescription. If you are already taking carbamazepine, do not stop it based on a raw file alone. Stopping epilepsy medicine suddenly can cause seizures.

Seek urgent care if you are taking carbamazepine and develop fever, mouth sores, sore throat, skin pain or blisters, whatever your HLA type. Early SJS can look like a mild rash or flu. Not every rash is SJS, but early SJS can be mistaken for one.

What HealthOS does not report

The free HealthOS DNA report reads a raw file and reports many things: traits, pharmacogenomics, carrier findings and ancestry. Its medication response list includes HLA-B findings for two specific drug safety questions, one HIV medicine and one gout medicine. It does not include a carbamazepine or HLA-B15:02 call. If your question is about carbamazepine safety, the useful next step is a clinical HLA-B15:02 test through a doctor.

healthosx.com/dna

The download steps for 23andMe, on the page itself.

healthosx.com/dna

The short version: what is worth acting on, first.

If you want to see what your raw file does support for traits, medication response and carrier-relevant findings, open the free DNA tool. It reads a 23andMe, AncestryDNA, MyHeritage or whole-genome VCF file in the browser and reports the results without payment.