To the Editor.
—I was interested in reading an article by Sridama and co-workers1 concerning HLA immunogenetic heterogeneity within patients with Graves' disease. These authors demonstrated that black Americans with Graves' disease showed an increased prevalence of HLA-DRw6 rather than the HLA-DR3 association found in white patients with Graves' disease. It is important to note that Angelini and co-workers2 had shown that at the genomic level of the polymorphisms of HLA-D subregions, using oligonucleotide probes, that HLA-DRw6 not only consists of at least two subtypes, but that these two subtypes cross-react with appropriate probes to the HLA-DR3 subregion. It is likely that this type of approach will have a more important predictive value in the study of the association of HLA and disease than the more traditional microcytotoxic assay approach. Of importance, however, is to realize that HLA-DRw6 and HLA-DR3 are not as distinct as the authors suggest.