Sir

I read with interest the Commentary by M. Cavazzana-Calvo and colleagues on “The future of gene therapy” (Nature 427, 779–781; 2004). However, readers should be aware that the statistics used to produce the map shown on page 781, “Number of approved gene-therapy trials”, are incomplete.

The map, using data compiled from available sources by the Wiley Journal of Gene Medicine, indicated that no gene-therapy trials have been performed in Norway. Yet, according to the Norwegian Directorate of Health, which approves such studies, seven trials were performed before 2004 — six at the Norwegian Radium Hospital and one at the National Hospital, both in Oslo.

For Norway, this is not just a question of incomplete statistics. When the first application for a gene-therapy trial was rejected by the Norwegian Board of Health in 1996, on the basis of sound scientific advice, rumours circulated in the international community that Norwegian authorities were hostile towards gene therapy. Your map supports this impression. Yet, during the past five years the Norwegian Ministry of Health has funded an ambitious grant programme to help scientists in Norway acquire internationally competitive competence in gene therapy.

Some years ago, I participated in a technology-assessment study of gene therapy organized by the Norwegian Center for Health Technology Assessment, in which the Wiley, Medline, EMBASE and US National Institutes of Health databases were searched for information on clinical trials. This resulted in a much more complete survey, although there is still no single authoritative source for such information.