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We are tempted to speculate that the pressor effect of water drinking is mediated by gastric distension. Indeed, distension of abdominal hollow viscera leads to a sympathetically mediated rise in blood pressure. Whether water drinking causes gastric distension sufficient to increase sympathetic tone is not known. Furthermore, in dogs, gastric infusion of distilled water elicits a two-fold greater pressor response than infusion of the same volume of normal saline or balloon gastric distension.1 In people, infusion of hypo-osmolar solutions through a gastric tube causes a greater increase in sweat production (a sympathetic response) than does infusion of iso-osmolar solutions. 2 Therefore, the pressor effect of water drinking may not be due to mechanical distension of the stomach alone, but may result from a combination of mechanical and osmotic stimuli. We agree that it seems counterintuitive to suggest that a sympathetically mediated response could be exaggerated in autonomic failure. The common notion that autonomic faulure is simply a complete loss of autonomic function is challenged by pharmacological studies that use ganglionic and ␣-adrenoreceptor blockade, which have shown that residual sympathetic function is present in a large subgroup of autonomic failure patients. Indeed, in multiple system atrophy patients, residual sympathetic tone is sufficient to cause hypertension in the supine position.3 Furthermore, this residual sympathetic function can be activated as shown by the observation that yohimbine, a sympathetic stimulant, causes a profound increase in blood pressure in a large subgroup of autonomic failure patients.4 Because autonomic failure patients are hypersensitive to directlyacting vasoconstrictors,4 and because impairment of autonomic function results in a substantial impairment of baroreflex buffering, 5 even a slight increase in norepinephrine release may profoundly raise blood pressure in these patients. Although autonomic failure patients may be unable to increase sympathetic tone sufficiently to overcome the physiological stress of upright posture, water drinking nonetheless seems to cause sympathetic activation, which, in conjunction with baroreflex debuffering, is sufficient to significantly increase blood pressure in the seated position. *Jens Jordan, John R Shannon, David Robertson Clinical Research Centre, Franz Volhard Clinic, Berlin, Germany; and *Autonomic Dysfunction Center, Vanderbilt University, Nashville, TN 37222, USA

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1

Nakai M. Cardiovascular responses to gastric hypo-osmolar stimulation in anesthetized dogs. Japan J Physiol 1993; 43: 335–46. 2 Haberich FJ. Osmoreception in the portal circulation. Fed Proc 1968; 27: 1137–41. 3 Jordan J, Shannon JR, Black BK, Pohar B, Robertson D, Biaggioni I. Mechanisms of supine hypertension in autonomic failure. Circulation 1998; 98 (suppl 1): I337. 4 Jordan J, Shannon JR, Biaggioni I, Norman R, Black BK, Robertson D. Contrasting actions of pressor agents in severe autonomic failure. Am J Med 1998; 105: 116–24. 5 Shannon JR, Jordan J, Black BK, Costa F, Robertson D. Uncoupling of the baroreflex by NN-cholinergic blockade in dissecting the components of cardiovascular regulation. Hypertension 1998; 32: 101–07.

Warfarin dose requirement and CYP2C9 polymorphisms Sir—Guruprasad Aithal and colleagues (Feb 27, p 717)1 record a strong association between CYP2C9 variant alleles and low warfarin dose requirements in randomly selected patients attending an anticoagulation clinic. We have quantified dietary composition over 8 weeks in 50 patients attending our anticoagulation clinic and consuming a normal diet. We showed2 that daily intake of vitamin K greater than 250 ␮g was associated with increased warfarin dose requirements in 16 (32%) patients. These patients had lower international normalised ratio (INR) values on day 5 of warfarin therapy (median 1·9 vs 3·0, p<0·001), needed more warfarin to achieve INR values of greater than 2·0 (mean [SD] 32·0 mg vs 25·4 [9·2] mg, p<0·01), and needed higher maintenance steady-state warfarin doses to maintain target INR values (5·7 [1·7] mg per day vs 3·5 [1·0] mg per day, p<0·001) than patients with vitamin K intake 250 ␮g per day. We suggest that the differences in warfarin sensitivity that Aithal and colleagues show could have resulted from differences in dietary vitamin K consumption, which were not accounted for in their study.

Authors’ reply Sir—Warfarin competitively antagonises vitamin K, which is necessary for the production of the active clotting factors II, VII, IX, and X in the liver. Hence, it is not surprising that daily dietary intake of vitamin K has an effect on warfarin dose requirement. However, the difference that Hillel Halkin and Aharon Lubetsky report in the dose requirement between two groups with daily intake of vitamin K of greater than 250 ␮g and less than 250 ␮g seems small (5·7 [1·7] mg vs 3·5 [1·0] mg, respectively). Daily warfarin requirements in these two groups fall in the range of daily doses (3–9 mg) of most patients receiving warfarin. 1 Clinical implications of assessing daily vtamin K intake are unclear. In our study patients in the low-dose group had a daily warfarin dose requirement of 1·5 mg or less, which was below 10th centile for the entire group of patients (n=828) registered with the anticoagulant clinic. Individuals in the low-dose group were six times more likely to carry one or more CYP2C9 variant alleles and four times more likely to have major bleeding complication than patients in the random clinic control group. We and others 2 have already discussed the potential clinical implications of these findings. We have also recruited 21 patients who required 8 mg or more of warfarin per day, which was above 90th centile for the entire group of patients on warfarin. Individuals in the highdose group are less likely to have a CYP2C9 variant allele than the community control group (odds ratio 0·25 [95% CI 0·07–0·90]). This finding underscores the impact of CYP2C9 variant alleles on the warfarin dose requirement. When 52 patients from the random

*Hillel Halkin, Aharon Lubetsky Department of Medicine and Division of Clinical Pharmacology, Sheba Medical Centre, Tel Hashomer 52621, Israel 1

2

Aithal GP, Day CP, Kesteven PJL, Daly AK. Association of polymorphisms in the cytochrome P450 CYP2C9 with warfarin dose requirements and risk of bleeding complications. Lancet 1999; 353: 717–19. Lubetsky A, Dekel-Stern E, Chetrit A, Lubin F, Halkin H. Vitamin K intake and sensitivity to warfarin in patients consuming regular diets. Thromb Haemos (in press).

Daily dose of warfarin according to CYP2C9 genotype in 52 controls Median (horizontal bar), interquartile range (shaded box), and 10–90th centiles shown. Medians are 4·25 mg (CYP2CP*1/*1), 3·5 mg (CYP2C9*1/*2 or CYP2C9*2/*2), and 2·5 mg (CYP2CP*1/*3).

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clinic control group (described in our study) were grouped according to their genotypes there was a significant correlation between mean daily warfarin dose and the genotype (figure). Patients with the CYP2C9*2 allele required a lower daily warfarin dose (3·7 [SD 1·9] mg) when compared with those homozygous for CYP2C9*1 (4·68 [2·1] mg), and individuals carrying CYP2C9*3 had the lowest (2·7 [1·3] mg) dose requirement (ANOVA, p=0·02). These findings are consistent with the fact that the CYP2C9*3 gene product is less than 5% as efficient as the wildtype enzyme, whereas the CYP2C9*2 enzyme shows about 12% of wild-type activity.3,4 CYP2C9 is unlikely to play a part in determining dietary vitamin K intake, and therefore vitamin K intake of individuals with variant alleles is unlikely to be lowered. Guruprasad P Aithal, Christopher P Day, Patrick J L Kesteven, *Ann K Daly Departments of Medicine and Pharmacological Sciences, University of Newcastle, Medical School, Newcastle upon Tyne, NE2 4HH, UK 1

British Society for Haematology. Guidelines on oral anticoagulation. J Clin Pathol 1990; 43: 177–83. 2 Mannucci PM. Genetic control of anticoagulation. Lancet 1999; 353: 688–89. 3 Rettie AE, Wienkers LC, Gonzalez FJ, Trager WF, Korzekwa KR. Impaired Swarfarin metabolism catalyzed by R144C allelic variant of CYP2C9. Pharmacogenetics 1994; 4: 39–42. 4 Haining RL, Hunter AP, Veronese ME, Trager WF, Rettie AE. Allelic variants of human cytochrome P450 2C9: baculovirusmediated expression purification, structural characterization substrate stereoselectivity and prochiral selectivity of the wild-type and I359L mutant forms. Arch Biochem Biophys 1996; 333: 447–58.

Management of cer vical intraepithelial neoplasia Sir—J Thomas Cox (March 13, p 857)1 comments on management of cervical inraepithelial neoplasia (CIN). CIN should be thought of as a heterogeneous group of precursor lesions for invasive cervical cancer. Because of conservative treatment of the premalignant stage, a reduction in the risk of invasive cervical cancer can be accomplished. However, there is considerable risk of overtreatment for these lesions. The peak incidence of cervical dysplasia is at age 28–34 years, although the risk of progression to invasive cervical cancer at these ages is very low. The biological behaviour of these lesions is difficult to predict. Some

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lesions will progress, whereas most will persist or even regress. The lesions that will progress seem impossible to distinguish prospectively from those that will regress. Therapy is the most important factor in preventing the persistence of recurrence of these lesions. 1 Other risk factors mentioned were age, human papillomavirus positivity, and previous treatment for CIN. We would emphasise the importance of two well known factors: angiogenesis and mitotic activity. In a study of 75 patients with severe cervical dysplasia (CIN grade III) and in 20 patients with microinvasive grade Ia1 squamous carcinoma of the cervix we noted that the microvessel density and mitotic activity progressed from non-invasive to invasive.2 The onset of angiogenesis that occurs during the premalignant dysplastic stage in human cervical cancer is unique. In most tumours neovascularisations appear when the tumour is already in situ. the substantial increase in microvessel density during progression from noninvasive (CIN grade III) to microinvasive squamous carcinoma underscores the importance of a n g i o g e n e s i s . 2,3 This step is better evaluated by the prognostic role that greater microvessel density has in predicting shorter disease-free or overall survival in invasive cervical cancer.3 On the basis of these findings we are tempted to suggest that antiangiogenesis therapy not only has a place in the treatment of an invasive carcinoma but also in preventing the progression to invasive carcinoma.4 Genetic alterations arise during the transformation of cells from a premalignant to a malignant state. The greater proliferation from noninvasive to microinvasive carcinomas suggests that the genetic alteration in CIN grade III induces a malignant transformation which also explains why the proliferation activity is higher in recurring CIN III lesions. In CIN III lesions there may be an association between angiogenesis, proliferation activity, and progression of cervical dysplastic lesions to an invasive carcinoma. These features seem to be associated with more aggressive behaviour of the lesion and could be used to identify women who are at high risk. Wiebren Tjalma Division Gynaecological Oncology, University Hospital of Antwerp, 2650 Antwerp, Belgium 1

2

Cox JT. The management of cervical intraepithelial neoplasia. Lancet 1999; 353: 857–59. Tjalma W. Apoptosis and angiogenesis in

human uterine cervical cancer [PhD thesis]. Antwerp: Antwerp University, 1999. 3 Tjalma W, Van Marck E, Weyler J, et al. Quantification and prognostic relevance of angiogenic parameters in invasive cervical cancer. Br J Cancer 1998; 78: 170–74. 4. Harris AL. Antiangiogenesis for cancer therapy. Lancet 1997; 349 (suppl II): 13–15.

Familial papillary th yroid microcarcinoma Sir—Giovanni Lupoli and colleagues’ (Feb 20, p 637)1 description of familial thyroid microcarcinoma prompts us to report two such cases. A 58-year old woman was referred in 1994 by her family physician because of a cervical mass. An ecography disclosed a diffuse goitre, with no nodules, and chest radiography and thyroid function test showed no abnormalities. 1 year later, the patient was again referred for suspected thyroid malignant disease after a solitary nodule had been detected on thorax radiography undertaken for unrelated reasons. An hyperechoic lesion was then noted in a new thyroid echography, and the cytology of the material obtained by fine-needle aspiration indicated papillary thyroid carcinoma. The thyroid was surgically removed, and the pathology examination disclosed a wellencapsulated 7 mm papillary thyroid microcarcinoma, with no capsule or vessel invasion, and no metastases. Uptake of 131-labelled iodine in different pulmonary lesions was observed and ablation with this radionuclide was done. 6 months later the patient developed progressive dyspnoea and a bronchoalveolar lavage showed cells that indicated bronchoalveolar carcinoma. Despite multiple therapeutic measures, the patient died in 1995. The necropsy showed massive and bilateral bronchoalveolar carcinoma. 2 years later, in 1997, the patient’s daughter, a 33-year-old woman, consulted us because she had noticed a cervical mass. Physical examination disclosed a 1 cm well delimitated nodule in the right thyroid lobule. Echography showed a 9 mm lesion and the fineneedle aspiration yielded a benign cytology, compatible with nodular hyperplasia. The patient’s anxiety prompted us to repeat the exam 6 months later, and the new fine-needle aspiration then showed different cells with clefted nucleous and characteristics of papillary thyroid carcinoma. The analysis of total thyroidectomy showed different areas of thyroiditis and a 7 mm well encapsulated thyroid

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