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Genewatch: Sex change priest in mercy dash to palace shock!

One of the characteristics of health care that attracts a lot of attention is the time it takes for ideas of proven effectiveness to enter clinical practice. The other side of the coin is the rapid dissemination of interventions of unproven effectiveness - sometimes without formal identification of possible harm. The book review on anti-arrhythmic drugs in Bandolier 23 is a short but good example of this.

Factor V Leiden

This gene is an important risk factor for thrombosis, involved in perhaps 15% of deep-vein thrombosis in the under-70s and up to 50% of familial thromboses. An important paper in the Lancet [1] has shown that the allele is common in European populations, but virtually unknown in several other populations.

The overall frequency of the allele in European and UK populations is 4.4%, and highest in Greeks at 7%.

The authors of the study emphasised very clearly at the end of their report: "Factor V Leiden is an important risk factor for venous thrombosis. The high prevalence suggests that prospective trials to assess the medical and economic desirability of screening before surgery and pregnancy in Europeans should be undertaken".


When a story about the study appeared in Doctor magazine about five days after the Lancet publication, the tone of the message was very different:

"Gene tests point to pill clots peril"

Although not quite in the class of "Sex change priest in mercy dash to palace shock" (always said to be the headline writer's acme), this is still fairly startling and implies that action should be taken.

The story linked the factor V Leiden research to the "pill scare" of October. They properly report the principal author as saying that the advantages of screening need to be offset against the consumption of resources, but with this headline, as opposed to the final sentence of the Lancet paper, they have moved implementation a notch nearer - emphasising particularly that many hospitals can provide this test. We know from colleagues in general practice and family planning that factor V Leiden tests are being offered at £25 a time.

What should be done about this gene? The answer, so far as the clinician or family planning doctor is concerned, is nothing. Testing for factor V Leiden raises an interesting possibility, but until the test has been tested it should not be used. Well conducted studies will provide answers about the appropriate place of testing, and what benefits or harms will accrue.


  1. DC Rees, M Cox, JB Clegg. World distribution of factor V Leiden. Lancet 1995 346: 1133-34.

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