rs9275328 — HLA-DQB1 DQB1 region

HLA-DQB1 Region — Completing the DR15 Three-SNP Panel for MS, SLE, and Narcolepsy

On chromosome 6, tucked in the intergenic stretch between HLA-DQB1 and HLA-DQA2 at position 32,699,045 (GRCh38), sits rs9275328 — the third pillar of the DR15 haplotype tag panel. Its C allele marks the presence of DQB1*06:02¹¹ DQB1*06:02
The HLA-DQ beta-1 chain allele that completes the DR15 haplotype: DRB1*15:01 + DQA1*01:02 + DQB1*06:02. These three genes are so tightly co-inherited across populations that a single SNP in each flanking region can identify the whole haplotype block with high accuracy, the allele that encodes the DQ beta chain partnering with DQA1*01:02 to form the most strongly MS-associated HLA-DQ heterodimer known. Together with rs3135388 (DRB1 side) and rs9271366 (DQA1 side), this SNP closes a three-locus surveillance net: when all three risk alleles are present, the DR15 haplotype is identified with the highest possible confidence from standard genotyping data.

HLA-DQB1 encodes the beta chain of the HLA-DQ class II antigen-presenting molecule. The beta chain forms the floor and one wall of the peptide-binding groove, and DQB1*06:02 creates a groove geometry that, in combination with the DQA1*01:02 alpha chain, is uniquely permissive for presenting myelin and oligodendrocyte peptides to auto-reactive CD4+ T cells. This same DQA1*01:02/DQB1*06:02 combination also drives narcolepsy risk through a distinct mechanism: it presents hypocretin-neuron-derived peptides that, after molecular mimicry triggered by viral infection or vaccination, are targeted by cytotoxic immune responses that destroy the hypothalamic hypocretin-producing neurons responsible for wakefulness regulation.

The Mechanism

rs9275328 sits approximately 31 kb downstream of the HLA-DQB1 gene body (GRCh38 gene end ~32,668,383; SNP at 32,699,045) and approximately 2 kb upstream of HLA-DQA2. Like rs9271366, it functions as a haplotype tag in strong linkage disequilibrium²² linkage disequilibrium
LD with D'=0.941 between rs9271366 and rs9275328 (Chai et al. 2013), meaning the two alleles are almost always inherited together; r²=0.065 indicates they are not perfectly correlated but the haplotype GC tags a consistent biological state with the DQB1*06:02 allele across the DR15 haplotype block.

The C allele of rs9275328 is the DR15 haplotype allele. The T allele marks non-DR15 chromosomes and, when present as a heterozygote (CT), breaks up the homozygous DR15 state — which is why the CT genotype itself showed a protective OR in the Chai SLE cohort. The high DQB1 expression³³ high DQB1 expression
15.7-fold higher DQB1 expression in DR15 haplotype carriers documented in the rs3135388 eQTL study applies here too: the C allele at rs9275328 co-segregates with all the regulatory machinery driving elevated DRB1*15:01, DRB5*01:01, and DQB1*06:02 expression. The DQB1*06:02 beta chain is expressed on all antigen-presenting cell surfaces in CC homozygotes, dramatically increasing the capacity for DR15-type self-antigen presentation in the thymus and periphery.

The Evidence

The SLE evidence is direct. Chai et al. 2013⁴⁴ Chai et al. 2013
360 Malaysian SLE patients vs 430 healthy controls across Malay, Chinese, and Indian ethnicities; TaqMan genotyping of both rs9275328 and rs9271366 found that the C allele and CC genotype at rs9275328 increased SLE susceptibility in Malays and Chinese (OR > 1, p < 0.05), while the minor T allele and CT heterozygotes were protective (OR < 1, p < 0.05). The haplotype GC (rs9271366-G / rs9275328-C) reached genome-wide significance after 10,000 permutation tests. Multifactor dimensionality reduction testing identified the GG/CC and AG/CC genotype combinations as the high-risk class, directly implicating rs9275328-CC as a required component of the highest-risk SLE genotype.

For MS, the DQB1*06:02 allele that rs9275328-C tags has well-established independent risk contribution. Fine-mapping the MHC in MS⁵⁵ Fine-mapping the MHC in MS
International MHC fine-mapping studies across thousands of patients established that the full DR15 haplotype (DRB1*15:01/DQA1*01:02/DQB1*06:02) drives MS risk, with heterozygous DR15 carriers at OR approximately 2.1–2.8 and homozygotes at OR approximately 4–6 compared to non-carriers. The DQB1*06:02 beta chain forms the antigen-presenting surface that displays myelin peptides⁶⁶ antigen-presenting surface that displays myelin peptides
Including MBP, MOG, and OSP peptides that are targets of auto-reactive CD4+ T cells in MS — a function independent of DRB1*15:01 that explains why DQB1*06:02 adds to MS risk beyond the DRB1 contribution alone.

Narcolepsy adds a third condition to this SNP's profile. A systematic meta-analysis across four ethnic groups⁷⁷ A systematic meta-analysis across four ethnic groups
Liblau et al. 2018, 30,000+ subjects found HLA-DQB1*06:02 confers an odds ratio of 24.1 (CI 14.6–39.5) for narcolepsy type 1 — one of the largest genetic effect sizes recorded for any common variant. Over 90% of narcolepsy with cataplexy patients in European and East Asian populations carry at least one copy of DQB1*06:02, compared to 15–25% of controls. rs9275328-C, as a tag for this allele, captures this extraordinary narcolepsy susceptibility signal.

Practical Implications

rs9275328-C completes the three-SNP DR15 panel alongside rs3135388 and rs9271366. When all three risk alleles are concordant (A at rs3135388, G at rs9271366, C at rs9275328), DR15 haplotype identification is near-certain from standard genotyping data. For CC homozygotes with both other DR15 tags also homozygous, the combined evidence represents the highest HLA-based MS and narcolepsy genetic risk configuration captured by this platform.

The modifiable intervention is the same as for the other two DR15 tags: vitamin D optimization. The vitamin D response element in the DRB1*15:01 promoter⁸⁸ vitamin D response element in the DRB1*15:01 promoter
Ramagopalan et al. 2009 — the VDR binding site in the DRB1*15:01 promoter means vitamin D directly regulates expression of the MS-risk allele operates across the whole haplotype block, and DQB1*06:02 expression co-varies with DRB1*15:01 regulation. Vitamin D insufficiency may amplify DR15 allele expression; maintaining serum 25(OH)D above 40 ng/mL is the primary evidence-backed modifiable lever.

For narcolepsy, the key practical implication is recognising excessive daytime sleepiness combined with sudden muscle weakness triggered by strong emotions (cataplexy) as a specific clinical pattern warranting hypocretin/orexin testing. Early diagnosis enables treatment with sodium oxybate or pitolisant that dramatically improves quality of life.

Interactions

rs9275328 is the DQB1-side tag for the same DR15 haplotype block tagged by rs3135388 (DRB1 side) and rs9271366 (DQA1 side). In the Chai SLE study, the haplotype GC (rs9271366-G + rs9275328-C) and the MDR high-risk combination GG/CC (rs9271366/rs9275328) demonstrated multiplicative interaction: homozygous DR15 at both loci produced the highest SLE risk class. The DR15 haplotype block has D'=0.941 between rs9271366 and rs9275328, indicating very strong but not perfect LD — meaning the two SNPs occasionally separate on different chromosomes, and concordant genotyping across all three tag SNPs reduces false positive/negative haplotype calls. The narcolepsy risk from DQB1*06:02 is partially separable from the MS risk of the full DR15 haplotype: DQA1*01:02 is required as co-receptor partner for narcolepsy, making the DQA1/DQB1 pair (captured by rs9271366 + rs9275328) the most proximal genetic risk unit for narcolepsy type 1.