927

Smear takers should concentrate on providing high quality cervical smears, containing endocervical as well as squamous cells, with immediate fixation. The cytologist should report on these quality criteria. The provision of the best devices (spatula with cytobrush or ’Cervex’), training in techniques, and feed-back on adequacy of smears should lead to a high level of sampling quality. We think this is more important than whether the lack of endocervical cells should be reason for an early repeat cervical smear. We also suggest that publications about cervical intraepithelial neoplasia, especially those on cervical screening, should provide information on sampling quality. Whenever possible, an inter-observer assessment should also be included. Department of General Practice, State University Maastricht, 6200 MD Maastrich, Netherlands

F. BUNTINX H. F. J. M. CREBOLDER J. A. KNOTTNERUS

Department of Gynaecology, University Hospital, Maastricht

G. G. M. ESSED

The

Division of Immunological Medicine, MRC Clinical Research Centre, Harrow HA1 3UJ, UK

powerful placebo

concerned about Professor Ernst and colleagues’ report (March 9, p 611). The ethics of prescribing a placebo preparation outside a clinical trial, whether ointment or tablet, have to be questioned. Many chronic, subjectively reported symptoms, such as they describe, respond well to medical consultation alone. 85% of patients referred to a specialist breast clinic with breast pain (mastalgia) do not need active treatment and, of those treated, a clinically useful placebo response occurs in around 19%.1 Active drug treatments used in mastalgia such as danazol, bromocriptine, and evening primrose oil all produce a significantly greater irnprovement than placebo, whereas progestogens do not, and therefore should not be prescribed in mastalgia. I would suggest that if, as Ernst et al state, in patients with varicose veins placebo ointments do produce as good a response as pharmacologically active ones, it is because ointments are not the treatment of choice for symptoms of this condition.

SIR,-I

am

Department of Surgery, University Hospital of South Manchester, West Didsbury, Manchester M20 8LR, UK 1

the analogous sites on the other subtypes, despite sequence similarities at residues other than position 59. There may be other reasons for the rarity of AS and related disorders in certain racial groups. HLA-B27-positive first-degree relatives of B27 AS patients have a 5-16-fold higher incidence of the disease than unrelated B27 subjects,’,’ pointing to another strongly predisposing gene or group of genes. The location and nature of this second AS locus is unknown, but its frequency in certain populations might well explain the rarity of these disorders. A further complication arises when geographically diverse populations are examined because exposure to postulated environmental factors2 may also vary. The notion of a reactive sulphydryl group at the B27 epitope is not necessarily incompatible with the "arthritogenic peptide" model discussed by Hill et al. Reaction with the sulphydryl side chain of Cys67 might be critical in B27 forming an unusually stable or stoichiometrically rigid interaction with a cysteine-containing bacterial peptide,7 or in controlling access to portions of the antigen presentation groove on B27.2

C. A. GATELEY

Inflammation Research Group, London Hospital Medical College

I. L. MACLEAN

J. R. ARCHER M. A. WHELAN

1. El-Zaatari FAK, Sams KC, Taurog JD. In vitro mutagenesis of HLA-B27. Amino add substitutions at position 67 disrupt anti-B27 monoclonal antibody binding in direct relation to the size of the substituted side chain. J Immunol 1990; 144: 1512-17. 2. Benjamin R, Parham P. Guilt by association: HLA-B27 and ankylosing spondylitis. Immunol Today 1990; 11: 137-42. 3. Archer JR, Whelan MA, Badakere SS, MacLean IL, Archer IVJ, Winrow VR. Effect of a free sulphydryl group on expression of HLA-B27. Scand J Rheumatol 1990; 87: 44-50. 4. MacLean IL, Winrow VR, Perrett D, Archer JR. Status of an unpaired thiol group on the HLA-B27 epitope. Clin Exp Immunol 1989; 77: 417-21. 5. Calin A, Marder A, Becks E, Bums T. Genetic differences between B27 positive patients with ankylosing spondylitis and B27 positive healthy controls. Arthritis Rheum 1986; 26: 1460-64 6. van der Linden SM, Valkenburg HA, de Jongh BM, Cats A. The risk of developing ankylosing spondylitis in HLA-B27 positive individuals: a comparison of relatives of spondylitis patients with the general population. Arthritis Rheum 1984; 27: 241-49. 7. Stieglitz H, Fosmire S, Lipsky P Identification of a 2-Md plasmid from Shigella flexnen associated with reactive arthritis. Arthritis Rheum 1989; 32: 937-46.

Gateley CA, Mansel RE. Management ofcyclical breast pain. Br J Hosp Med 1990; 43:

Mitochondrial leucine tRNA mutation in neurological diseases

330-32

HLA-B27 subtypes SjR,—Dr Hill and colleagues (March 16, p 640) used the polymerase chain reaction and dot-blot hybridisation to show that 11 of 18 healthy HLA-B27-positive Gambians had the B*2703 subtype. They postulate that the rarity of ankylosing spondylitis (AS) and other B27-related disorders in African blacks is due to B*2703 conferring a much lower risk than the other subtypes. B*2703 differs from the AS-associated B*2705 subtype by a single Tyr->His substitution at position 59 on the al domain of the molecule. The B27 epitope features an unpaired cysteine residue at aminoacid 67.1 A unique combination of neighbouring aminoacids includes asparagine at position 97 and lysine at position 70,2 whose positively charged side chain may favour the more reactive-Ssulphydryl side chain variant at the adjacent Cys67.3 Sulphydryl reactivity of a proportion of B27 molecules’ suggests that the fine conformation of the epitope will vary according to the oxidative state of this cysteine, the "altered self’ model. Hill et al cite the postulated absence of disease predisposition with B*2703, which shares Cys67, Lys70, and Asn97 with the other B27 subtypes, as evidence against this model. We have two major reservations about this argument. As confmned by their observation that cytotoxic T lymphocytes responding to B*2702 and B*2705 fail to recognise B*2703, the conformation of this region will be different in B*2703. The accessibility and reactive state of Cys67 may be very different from

SIR,-Mutations in mitochondrial DNA (mtDNA) have been several neurological diseases, including chronic progressive external ophthalmoplegia (CPEO), Kearns-Sayre syndrome,! myoclonus epilepsy and ragged-red fibres (MERRF),22 and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS).3,4 Two independent Japanese groups have reported a point mutation in mitochondrial leucine tRNA (UUR) -namely an A-to-G transition at position 3234-in 26 out of 313 and in all of 44 patients with MELAS. This mutation was also detected in one patient with CPEO (1/29)3 who had a positive family history of mitochondrial disease. To verify the significance of this mutation in other populations, we studied mtDNA from American probands with mitochondrial encephalomyopathies. An mtDNA region bracketing the tRNA leucine gene was synthesised by polymerase chain reaction amplification, from positions 1591 (12S rRNA) to 3650 (ND-1), and was digested with the restriction enzyme ApaI. The 3243 mutation creates an Apal recognition site (GAGCCC to GGGCCC) and the wild-type 2059 base PCR product is cleaved into 1652 base and 407 base products. We detected the 3243 mutation in all of 6 probands with MELAS, in 1 patient with Kearns-Sayre syndrome, and in another with CPEO. Neither the patient with Kearns-Sayre syndrome nor the CPEO patient had a positive family history of mitochondrial disease. None of these 8 patients had a detectable mtDNA deletion by Southern blot analysis or by widely interspaced primer PCR.S In each patient and tissue examined, the 3243 mutation coexisted with found in