Found twice, in two populations, with almost nothing in common between the answers. That is the finding — and it is a lesson about what "the genetics of a disease" means when the disease was only studied in one place.
Vitiligo is an autoimmune disease in which the immune system destroys melanocytes, the cells that make pigment. The result is patches of skin and hair that lose their colour. It is not dangerous and it is not contagious, and it carries an elevated risk of other autoimmune conditions.
In 2010, two genome-wide studies of generalized vitiligo were published within months of each other, in different populations.
One studied Chinese Han participants: 1,117 cases and 1,429 controls, with replication in 5,910 cases and 9,916 controls plus a Chinese Uygur set of 713 and 824. It found two independent signals inside the MHC and a locus at 6q27.
The other studied European-ancestry patients: 1,514 cases against 2,813 controls across 579,146 positions, with two replication sets. It found autoimmunity loci and a variant in TYR — the gene for tyrosinase, the enzyme that makes pigment.
The two answers overlap far less than you would expect for the same disease.
Not that one study was wrong. Both were large and both replicated.
It means the phrase "the genetics of vitiligo" hides a question: whose. Populations differ in which variants are common, in which alleles sit near each other on a chromosome, and sometimes in which route to a disease is available at all. A scan finds what is variable in the people it looked at.
This is a general problem and vitiligo is an unusually clear case of it. The overwhelming majority of genome-wide studies have been done in European-ancestry cohorts, and every one of them carries this caveat whether or not it is printed.
The European study's TYR finding is worth a sentence on its own, because it is strange and it makes sense.
Tyrosinase is not an immune protein — it is the enzyme melanocytes use to make pigment. Its appearance here says the immune system is not attacking melanocytes at random; it is recognising something specific that melanocytes make. The target is the pigment machinery itself.
Vitiligo is diagnosed by looking at skin, sometimes with a Wood's lamp. No genotype is used, none of these positions predicts who will develop it, and treatment does not depend on any of them.
The two sources. Quan et al. (Nat Genet 2010) conducted a genome-wide association study of generalized vitiligo in the Chinese Han population, genotyping 1,117 cases and 1,429 controls, with the 34 most promising SNPs carried forward into 5,910 Chinese Han cases and 9,916 controls plus 713 Chinese Uygur cases and 824 controls. Two independent association signals were identified within the MHC (rs11966200, P combined 1.48e-48, OR 1.90; rs9468925, P combined 2.21e-33, OR 0.74), together with a 6q27 locus. Jin et al. (NEJM 2010) genotyped 579,146 SNPs in 1,514 patients of European-derived ancestry against 2,813 publicly available controls, testing 50 SNPs in two replication sets, and reported a variant of TYR alongside autoimmunity susceptibility loci.
The variants recorded here. rs2236313 near RNASET2 at 6q27, from the Chinese Han study; rs11203203 in UBASH3A, from the European study. UBASH3A is also associated with type 1 diabetes and coeliac disease, consistent with generalized vitiligo's established clustering with other autoimmune conditions.
The TYR finding. Tyrosinase is the rate-limiting enzyme of melanin synthesis and a known autoantigen in vitiligo. Its identification as a susceptibility locus supports an antigen-specific rather than a non-specific autoimmune process, and is an unusual instance of a GWAS naming the target of the autoimmunity rather than only the immune machinery.
Clinical boundary. Generalized vitiligo is diagnosed clinically, with Wood's lamp examination where the distinction from other depigmenting conditions is unclear. No genotype contributes to diagnosis, prognosis or treatment selection. The association with other autoimmune diseases — thyroid disease in particular — is clinically relevant but is assessed by history and thyroid function testing, not by genotype.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Vitiligo comes down to these specific, well-studied positions — not a diagnosis.
Because they looked at different populations, and populations differ in which variants are common and which alleles travel together. Neither was wrong. It means "the genetics of vitiligo" hides the question of whose — and almost every genome-wide study carries that caveat whether it prints it or not.
Because it is what the immune system is recognising. Tyrosinase is the enzyme melanocytes use to make pigment, and finding it here says the attack is not random — it is aimed at something specific those cells make.
It raises the risk, and thyroid disease is the common one. That is worth mentioning to a doctor, who will check it with a blood test. Several of the genes here are shared with type 1 diabetes and coeliac disease, which is the same fact seen from the genome.
No. It is diagnosed by looking at skin, sometimes with a Wood’s lamp. No position here predicts who develops it and none affects treatment.
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