Genetic polymorphism and drug-induced movement disorders.

Sir: We were interested to read the paper by Armstrong et a1 (1997) on drug-induced movement disorders in relation to the CYP2D6 genotype. We would agree that this important polymorphism may well be a contributory factor in more chronic druginduced movement disorders. G. D. I. Bates Blrm~ngham Children's Hospital. Ladywood M~ddleway, Ladywood, Birmtngham B16 8ET A. E. van Woerkom, 0. Lopes Queen Elizabeth Psychiatric Hospital, M~ndelsohn Way, Birmingham 815 2TZ R.Waring, L. Kiovrza Department of B~ochemlstry, University of Birm~ngham, Edgbaston, Birm~ngham be earlier for married women than for married men. The same relation holds for singles. But, as above, these differences are due to a trival demographic effect. If there is a real association between gender and schizophrenia in the sense that onset is later for women, then this difference is reduced when comparing married women with married men and single women with single men. Thus differences in the age structures between married and single persons in the population explain, at least in part, the effects of marital status and gender on age at onset, described by ~ a b l e n s k ~ & ole.-The differences in age at onset between developing and developed countries may be anributed to different demographic structures in these countries. We do not deny these effects, but to disentangle demographic effects from real effects the age structures of the underlying population must be taken into account when analysing the data.