HLA class II polymorphisms in Spanish melanoma patients: homozygosity for HLA-DQA1 locus can be a potential melanoma risk factor.

BACKGROUND

The association of melanoma with HLA class II loci is under extensive debate. Different investigators have found discrepant results due to, at least in part, sample size, patient series heterogeneity, choice of control population and differences in the techniques employed for the detection of HLA antigens and alleles.

OBJECTIVES

This study was designed to analyse the possible association of melanoma with HLA class II loci with regard to different clinic pathological factors and to investigate other risk factors for melanoma susceptibility, such as HLA homozygosity.

PATIENTS AND METHODS

HLA-DRB1, -DQA1 and -DQB1 genotyping was performed for 117 eastern Spanish patients presenting with primary melanoma.

RESULTS

Although there were no significant alterations in the phenotypic frequencies of HLA-DQA1, -DQB1 or -DRB1 alleles in any subgroup of patients when compared with controls, patients exhibited a statistically significant increase in HLA-DQA1 homozygosity rate. This DQA1 homozygosity-specific association was particularly dependent on some features in melanoma patients such as light hair colour, skin type I or II, early age at diagnosis, absence of atypical naevi, or abscence of atypical naevus syndrome phenotype (aetiological fractions about 10-20%). Analysis of homozygosity for single DQA1 alleles showed an increased homozygosity rate for DQA10505 and DQA10301 in comparison with controls. These DQA1 alleles are in strong linkage disequilibrium with DQB10301 in white populations, and DQB10301 homozygous individuals were significantly increased in red in or fair-haired patients (relative risk 5.65).

CONCLUSIONS

Our results indicate that the contribution of HLA class II alleles to primary melanoma incidence is not significant in the Spanish population. However, homozygosity for the HLA-DQA1 locus (and, perhaps, for the HLA-DQB1*0301 allele) might be considered a potential risk factor for developing melanoma depending on the person's genetic background and, perhaps, on certain environmental conditions.