Editor,—I read with great interest the paper by Kilmartin et al.1 The incidence of 25% (six patients out of 24) of HLA-B51 among the 24 patients with Behçet’s disease is interpreted as showing a “primary association” between this HLA antigen and Behçet’s disease in Ireland.

In my opinion, the far reaching conclusions of these authors is questionable as the control group consisting of “96 healthy voluntary blood donors to the Blood Transfusion Service Board” may not be an adequate sample for comparison.

The HLA frequencies in the 24 patients with Behçet’s disease as outlined in Table 1 of their paper show that of the 52 HLA antigens tested, 20 antigens were absent (0.00 frequency) in the group of Behçet’s patients and were present in the control group. Moreover, four other HLA antigens (of the 52 tested) were absent in the control group and detected only in the patient group. The absence of 46% of the tested HLA antigens in either group and their presence in the other group indicate unequivocally that the group of volunteers chosen as control for the frequency of the HLA-B51 is inadequate. This paper thus exemplifies once again the need for proper controls …