A Study Of Risk Factors
Creutzfeldt-Jakob disease (CJD) is currently the most frequent transmissible subacute spongiform encephalopathy (TSSE) in humans. The cause of the most common form, sporadic CJD, remains unknown. There is no laboratory test for the disease and no curative treatment. Since 1990 CJD has been the focus of a European epidemiological study (directed, in France, by Annick Alperovitch, INSERM U360 <Epidemiology in neurology and psychopathology>, Paris). An article in the British journal the Lancet gives the results of the European network on risk factors for sporadic CJD.
90% of cases of CJD are "sporadic", meaning they strike people at random, independently of known biological or environmental causes. In this sense these cases differ from the new form of CJD ("new variant" CJD) described in 1996, which has been linked to bovine spongiform encephalopathy (BSE) (see inset).
Given the rarity of CJD (its yearly incidence is still less than one case per million inhabitants), only a very large survey study could identify the several hundred of cases of CJD required for a fine epidemiological analysis. A European network was launched in 1990 . It now counts five countries which, over 3 years, analyzed the risk factors for sporadic CJD. No study of this scale had previously been undertaken. Between 1993 and 1995 a questionnaire focusing on the patient's medical history, dietary habits and occupational environment was submitted to carers of the 405 notified subjects with sporadic CJD (most patients are too ill to answer themselves). All the patients included in the study had a firm diagnosis ruling out the new variant CJD described in 1996. The epidemiologists submitted the same questionnaire to 405 individuals forming a control population.
Comparison of the two sets of replies showed no link with previous surgery or blood transfusion, or consumption of beef, veal, lamb, cheese or milk. In contrast, the scientists identified a weak but significant association between certain factors and sporadic CJD, including consumption of raw meat or brain tissue, exposure to fertilizer manufactured from animal remains (horn and hoof), and activities bringing people into contact with skins, leathers and furs.
The researchers underline the fact that the study is only a first step, and that many questions remain to be answered. In particular, it is conceivable that the risk factors identified simply reflect another, unidentified habit or behavior. In addition, there is a risk of bias as in all epidemiological studies, particularly those based on indirect testimony. Finally, the authors themselves state that even if there is effectively a direct link between these risk factors and CJD, it would only explain a small number of sporadic cases (3 or 4 per year in France) and the French program on TSSE and prions. A new study is under way within the framework of the European Biomed 2 program (1997-1999).
Sporadic forms, which are most frequent in subjects over 60, account for about 90% of all cases of CJD. The remaining 10% are distributed among genetic forms, iatrogenic forms (treatment with pituitary hormone growth, dura mater transplants) and new variant CJD due to the BSE prion described in 1996.
For more informations :
Sources
Case-control study of risk factors of Creutzfeldt-Jakob disease in Europe during
1993-95
C.M. van Duijn1, N. Delasnerie-Lauprêtre2, C. Masullo3, I. Zerr4, R. de Silva5,
D.P.W.M. Wientjens1, J-P. Brandel2, T. Weber6, V. Bonavita7, M. Zeidler5, A.
Alpérovitch2, S. Poser3, E. Granieri8, A. Hofman1, R.G. Will5 for the European
Union (EU) Colloborative Study Group of Creutzfeld-Jakob disease (CJD)
1Department of epidemiology and biostatistics, Erasmus University Medical
School, Rotterdam, Netherlands
2U360 INSERM, Hôpital de la Salpêtrière, Paris, France
3Department of Neurology, Catholic University of Sacred Heart, Rome, Italy
4Clinic of neurology, Göttingen University , Germany
5CJD Surveillance Unit, Edinburg, United-Kingdom
6Marian Hospital, Hambourg, Germany
7Department of neurology, Frédéric II University, Naples, Italy
8Department of neurology, University of Ferrare, Ferrare, Italy
"The Lancet", 11 avril 1998, vol 351, n° 9109, pp 1081-1084
Journal
The Lancet