Clozapine-induced concordant agranulocytosis in monozygotic twins

Two monozygotic twin sisters were admitted to a psychiatric hospital and diagnosed as having first-episode schizophrenia. Clozapine treatment led to the complete remission of psychotic symptoms within a short time. In both twins the low leukocyte count was detected after 9 weeks of clozapine. Serological typing of the HLA system was performed and an identical pattern was detected in both twins: HLA-A: 28, 26; HLA-B: 49, 63; DR: 2 (vs 16), 12, 52; DQ:1. It is the first report of concordant manifestation of clozapine-induced agranulocytosis in monozygotic twins. Our case report of twins afflicted synchronously with schizophrenia and later with agranulocytosis after clozapine is of interest because it suggests that genetic factors may participate not only in timing of onset of schizophrenia, but also in the emergence and timing of agranulocytosis in response to clozapine treatment. ( Int J Psych Clin Pract 2001; 5:71-73).