Interaction Between Sex and HLA Type in Hodgkin's Disease

To the Editor.  —Weitkamp¹ recently published an intriguing report demonstrating an interaction between sex and HLA type in multiple sclerosis (MS). In his study, he found a striking excess of sex-concordant sibling pairs with MS.He cited an article of ours,² that reported a similar excess of sex-concordant sibling pairs with Hodgkin's disease, but he did so in a misleading way. He has used a method different from ours to derive expected numbers of like-sex and unlike-sex sibling pairs. Comparing our observed frequencies with the expected values he derived, he did not find the statistically significant excess of sex-concordant pairs that we had found. However, he applied his method to only a subset of the cases we reported, namely, those found in our review of the literature. If his approach is used to assess all of the Hodgkin's disease sibling pairs described in our article (our series of