187

of soya protein may be shared by increased intakes of other plant products that are high in phytate but either not consumed in quantity in Singapore or not assessed in the questionnaire Lee et al administer. Supported by the

US Department of Energy under contract DE-AC06-76RLO

1830

Pacific Northwest Laboratory, Richland, WA 99352, USA

RICHARD G. STEVENS

1. Cook JD. Adaptation in iron metabolism Am J Clin Nutr 1990; 51: 301-08. 2. Stevens RG, Jones DY, Micozzi MS, Taylor PR. Body iron stores and the nsk of cancer. N Engl J Med 1988; 319: 1047-52. 3. Weinberg ED. Iron withholding: a defense against infection and neoplasia. Physiol Rev 1984; 64: 65-102. 4 Halliwell B, Gutteridge JMC. Oxygen free radicals and iron in relation to biology and medicine: some problems and concepts. Arch Biochem Biophys 1986; 246: 501-14. 5. Thompson HJ, Kennedy K, Witt M, Juzefyk J. Effect of dietary iron deficiency or excess on the induction of mammary carcinogenesis by 1-methyl-1-nitrosourea. Carcinogenesis 1991; 12: 111-14. 6. Graf E, Eaton JW. Antioxidant functions of phytic acid. Free Radicals Biol Med 1990; 8: 61-69.

How good is HIV envelope glycoprotein vaccine as a T-lymphocyte stimulant? SIR,-Dr Cooney and colleagues’ results (March 9, p 567) show several important gaps that conceal a difficulty with the assessment of T-cell responses to vaccinated antigens. Although they identify a proliferative response post vaccination (table m), they do not present results of the assay with recombinant peptide on their patients’ lymphocytes before vaccination. Our experience with HIV protein and peptides,l and that of others with malarial antigen,2 is that healthy unprimed individuals frequently respond to many proteins or peptides in proliferative assays. Such responses are thought to be crossreactive responses by T cells primed to other antigens ("memory" cells), and are observed only in a small number of cells in any individualCooney et al do not describe the frequency of T cells responding to the peptide post vaccination, or the titration of the responses observed. These three measures should represent important considerations in the estimation of the efficacy of T-cell stimulation by a gp 160 vaccinia construct vaccine. ICRF Human Tumour

Immunology Group,

University College and Middlesex Schools of Medicine, London W1P 8BT, UK

C. MICHIE A. VYAKARNAM P. C. L. BEVERLEY

Matear P, Michie C, Beverley PCL. The proliferative response to HIV-1 gag p24 peptides is not strictly disease related. Int Immunol (in press). 2. Jones KR, Hickling JK, Targett GA, Playfair JH. Polyclonal in vitro proliferative responses from nonimmune donors to plasmodium falciparum malaria antigens require UCHL1 + (memory) T cells. Eur J Immunol 1990; 20: 307-15. 3. Michie C, Vyakarnam A, Beverley PCL. T cell responses to HIV-1 gag p24 peptides. (British Society for Immunology, Epitope Workshop, Charing Cross Hospital, 1.

Vyakarnam A,

April, 1991.)

*** This letter has been shown to Prof Corey and Dr Cooney, whose reply follows.-ED. L. SiR,—Dr Michie and colleagues are rightly concerned that the lymphoproliferative responses to gp160 that we observed post vaccination might represent non-specific proliferation to baculovirus proteins or other non-HIV antigens retained in the envelope preparation after protein purification. Although responses to this antigen were not assessed before vaccination several factors support the specificity of the responses seen post vaccination for HIV epitopes. First, 4 of the 5 individuals who responded to the baculovirus gp160 preparation (table in) also responded after vaccination to one or more additional HIV immunogens. One of the antigens, live LAV, has not elicited any non-specific responses in over a dozen

evaluations of responses sequentially, only recombinant virus recipients showed a response to psoraten/UV-inactivated virus on more than one occasion. These findings, together with the striking anamnestic responses to HIV seen after subsequent boosting of these recombinant vaccine recipients with soluble envelope protein given one year later,’ support the immunogenicity of this vaccinia gpl60 recombinant in vaccinia-primed as well as naive hosts. Division of Virology, University of Washington,

1.

Cooney EL, Corey L, Hu SL, et al. Enhanced immunogenicity in humans of an HIV subunit vaccine regimen employing priming with a vaccinia gp160 recombinant virus (vac/env) by boosting with recombinant HIV envelope glycoprotein (rgp160). (Presented at the Third Annual Meeting of the National Cooperative Vaccine Development Group for AIDS, San Francisco, October 1-5, 1990.)

Bleeding time SIR,-A rigorous scientific reappraisal of the bleeding-time test (June 15 editorial) is long overdue. The general belief that an aspirin a day keeps the doctor away and the more rational use of aspirin in obstetric’"* and cardiological practice presents not only the surgeon and haematologist but also the anaesthetist3 with a dilemma. Extradural anaesthesia is an effective method of pain relief during labour and is commonly used in the intrapartum management of the patient with pre-eclampsia. However, a bleeding diathesis is a contraindication to epidural anaesthesia so the anaesthetist has to do a risk-benefit analysis before offering an epidural anaesthetic to a patient with pre-eclampsia. For that he needs a specific, sensitive, cheap, and rapid bedside test to indicate whether the patient is at increased risk of an epidural haematoma. The bleeding-time test is the only one in current use but, as Rodgers and Levin point out,’ it is a poor predictor of clinically significant bleeding. Values ranging from 105 to 156minutes have been suggested as a cutoff in deciding whether an epidural anaesthetic would be safe but they have not been based on prospective clinical trials. Platelet aggregation studies take several hours, are expensive, and are only available in larger centres-and if aggregation is abnormal does this mean that the risk of bleeding is increased? Thromboelastography has not been evaluated as a predictor of bleeding in the patient taking regular aspirin. The time is right not only for a second look at the bleeding time test, but also for a concerted effort to fmd an adequate test of platelet function, so that obstetric anaesthetists can continue to offer epidural anaesthesia to patients with pre-eclampsia and still sleep soundly at night. M. H. CROSS

Department of Anaesthetics, Edgware General Hospital,

E. J. HAXBY

Middlesex HAS OAD, UK

P. N. ROBINSON

1. Uzal S, Beaufils M, Breert G, Bazm B, Capitant C, Paris J. Prevention of fetal growth retardation with low-dose aspirin: findings of the EPREDA trial. Lancet 1991; 337: 1427-31 2. Schiff E, Peleg E, Goldenberg M, Rosenthal T, Ruppin E. The use of aspirin to prevent pregnancy induced hypertension and lower the ratio of thromboxane A2 to prostacyclin in relatively high risk pregnancies. N Engl J Med 1989; 321: 351-56. 3. Editorial. Aspirin and extradural blocks. Br J Anaesthesia 1991; 66: 1-3. 4. Rodgers RPC, Levin J. A critical review of the bleeding time. Semin Thromb Hemostas

1990; 16: 1-20. 5. Laros K.

Coagulation disorders and haemoglobinopathies in the obstetric and surgical

In: Schnider SM, Levinson G, eds. Anaesthesia for obstetrics, 2nd ed. Baltimore: Williams & Wilkins, 1987: 263-73. 6. O’Sullivan G. Regional anaesthesia and aspirin. Anesthesiology 1990; 73: 359.

patient.

Stopping hiccoughs

uninfected individuals whom we have evaluated so far.

The other antigen preparation, psoraIen/UV-inactivated LAV, was available for use in assays throughout the study period and only 1 (6%) of 18 recombinant virus recipients responded to this immunogen before vaccination. Additionally, of 139 assays run on the 17 vaccinia controls in only 9 (6 % ) was a response to this antigen seen. In each instance the response was low, with a mean stimulation index of 6, compared with 20 among recombinant virus recipients who had a response to this immunogen. Moreover, in

LAWRENCE COREY ELIZABETH COONEY

Seattle, WA 98144, USA

SiR,-During a long period of retirement from clinical practice, I have made an observation which may be of interest. In the absence of patients my family and friends have been the subjects of experiment. An attack of hiccoughs may be socially embarrassing, and in a severely ill patient persistent hiccoughs can sometimes be distressing. The repeated spasms can be brought to a halt by pressing a finger firmly into each external auditory meatus for

188

twenty seconds or so. So far I have not found the manoeuvre to fail the hiccoughs to return. I imagine that the pressure on the meatus stimulates the auricular branch of the vagus, thus blocking momentarily the path of stimuli coming from the diaphragm or adjacent viscera. or

"Dacres", Alfnston, Sussex, UK

PHILIP READING

Chlamydia trachomatis detection and non-invasive sampling methods SIR,-Several points Dr Patel and colleagues (May 11, p 1169) make cannot pass without comment. Patel et al do not regard testing of early morning urine samples as feasible and test first-catch urine samples from men, irrespective of how long urination has been withheld. It is strange that they do not compare first-catch urine efficiency with that of testing early morning samples. If sensitive methods of detection are used, it is true that testing an early morning urine has no advantage.’ Unfortunately, it is difficult to determine the sensitivity of their methods. Although they confirm the positive results obtained by the NovoNordisk ELISA by Syva MicroTrak, they did not confirm the negative results and have probably been missing chlamydiae. One way to assess this would be to determine the prevalence of Chlamydia trachomatis in men with nongonococcal urethritis (NGU). Examination of the Sheffield data does not allow this, but if all the men with symptoms had NGU then 30% would have been chlamydia-positive-which is less, by about 20%, than would be expected with a sensitive method.2 An alternative explanation for the low prevalence rate, apart from lack of test sensitivity, is that swabs were not taken properly. No doubt the Sheffield group would argue that this does not matter because urine samples provide results that are better than those obtained by urethral swabbing (94% versus 72%). This may be true, but to infer that the results are in any way a vindication of the non-invasive approach when there is so much at fault would be wrong. For others, including ourselveswho have used a sensitive method of testing a urethral swab, swabbing is at least as sensitive as urine sampling. Finally, the boldness with which the Sheffield workers assert that urine sampling in women is of little value suggests that they have come to this conclusion on the basis of urine examinations. That they have done so is not mentioned. Urethral carriage of C trachomatis in only 1-3% of 455 new female attenders who they examined suggests an insensitive test, poor swabbing, or both. In a continuing study of women attending St Mary’s Hospital, as many urethral smears as cervical smears have been chlamydia-positive by MicroTrak; moreover, a centrifuged urine deposit has occasionally been the only specimen positive by MicroTrak. We are, therefore, unable to support Patel and colleagues’ contention that the detection of chlamydiae in urine probably represents contamination of the sample. Division of Sexually Transmitted Diseases, Clinical Research Centre, Harrow, and Jefferiss Wing, St Mary’s Hospital, London W2 1NY, UK

P. E. HAY P. HORNER B. J. THOMAS D. TAYLOR-ROBINSON

Department of Clinical Microbiology, University College Hospital, London WC1

G. L. RIDGWAY

1. Thomas BJ, Gilchrist C, Hay PE, Taylor-Robinson D. Simplification of procedures used to test urine samples for Chlamydia trachomatis. J Clin Pathol 1991; 44: 374-75 2. Hay PE, Thomas BJ, Gilchrist C, et al The value of unne samples from men with non-gonococccal urethritis for the detection of Chlamydia trachomatis. Genitourin Med 1991; 67: 124-28.

*** This letter has been shown to Dr Patel and his colleagues whose reply follows.-ED. L. SIR,-We are surprised that Dr Hay and his colleagues criticise our work when so many of our findings are in keeping with those of other independent workers. 1,2 Only recently Crowley et alz reported a comparison of urethral swabs with first-catch urines and their detection rates for Chlamydia trachomatis with enzyme

immunoassay (EIA) were 65-5% and 91%, respectively. The we presented were preliminary findings of a much larger investigation looking at many aspects of urine versus urethral testing. Our study was set up not to compare early morning urines with results

first-catch urine but to compare first-catch urines with urethral swabs, which we still believe to be the most practical clinical use for the test. Although symptoms are a poor discriminator for the presence of non-gonococcal urethritis (NGU), Hay et al attempt to determine the sensitivity of our methods by assuming that all men with symptoms have NGU. Not surprisingly they underestimate the probable sensitivity of our methods. There were 65 men with NGU of whom 25 (38%) had evidence of chlamydial infection. Before and during the study we have monitored the quality of sample collection. Direct immunofluorescence (DIF) on all urethral samples from new attenders yields only an extra 2% than do EIA tests.

The value of screening women with both urethral and cervical has been contested by many workers using sensitive testing.3 Our routine practice of cleaning the vulva before taking urethral swabs and the availability of tests to all patients rather than their restriction to a further selected high-risk group explains our low urethral detection rate. Hay et al seem to conclude that we are calling for the abandonment of sensitive testing (they themselves use a mixture of PCR and DIF). Unfortunately such techniques are not available to most clinics striving to offer chlamydia testing to all their patients; the reality remains a choice between various EIA methods.’ It is in the context of such a choice that we feel a first-catch urine test offers an excellent alternative to urethral swabbing. tests

Department of Genitourinary Medicine, Royal Hallamshire Hospital, Sheffield S10 2JF, UK

R. PATEL G. R. KINGHORN

Public Health Sheffield

G. KUDESIA R. VAN HEGAN

Laboratory Service,

EO, Paul ID, Milne D, et al. Non-invasive sampling method for detecting Chlamydia trachomatis. Lancet 1988, ii 1246-47. 2. Crowley T, Milne D, Paul ID, et al. Non-invasive diagnosis of Chlamydia trachomatis 1. Caul

3.

in males-time for a change? BSSI chlamydia symptoms, April 19, 1991: 79. Bradley MG, Hobson D, Lee N, et al. Chlamydial infections of the urethra in women

Genitourin Med 1985; 61: 371-75. 4. Radcliffe KW, Rowen D,

Mercey DE, et al. Survey of the management of Chlamydia

trachomatis infection of the

cervix

Genitourin Med 1991, 67: 41-43.

Genomic

imprinting

SiR,—Dr Lubinski and Professor Hall (May 25, p 1288) suggest that there is a mechanistic and possibly temporal relation between genomic imprinting (differential parental gene expression), monozygous twinning, and X-inactivation. This hypothesis rests upon discordant phenotypic expression of genetic disorders in monozygous twins, being more common in females. Numbers of published cases are small, however. It is unlikely discordance in phenotypic expression of genetic disorders in monozygous twins would by itself warrant publication since this would often be dismissed as being due to environmental effects. We suspect many such cases may remain unknown to the scientific community. This notion is exemplified by two pairs of monozygous 46,XX twins who have the devastating dementia and behavioural disorders characteristic of Rett syndrome. One set shows phenotypic concordance; in the other set one twin is severely affected, is of short stature (126 cm), and is wheelchair bound while the other is still mobile at age 26, of normal height (162 cm), and generally abler than expected in Rett syndrome. We have communicated these two cases to Lubinski and Hall, and suggest that it might be a good idea to create a register to accumulate data that will substantiate or refute their observation that discordance in phenotypic expression of genetic disorders is more common in monozygous female twins than in males. If there is a firm association between sex-chromosome constitution and phenotypic discordance in monozygous twins, how could this come about? We suggest differential spatial