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Mutations can inhibit this tumour-suppressive effect, and somaticmutations of the p53 gene have been found in a wide range oftumours, often with concomitant loss of the normal allele.6.7 Initial

reports for human bladder cancer,8 and our own work, revealed awide variety of point mutations in urothelial cancer. Mutations inp53 have been reported in most muscle-invasive bladder

carcinomas,4,8 but infrequently in non-invasive urothelial cancers.In this patient we found identical somatic cell alterations of thec-erbB-2 and p53 genes in renal cell and bladder tumours. The highlevel of c-erbB-2 gene amplification is rare in bladder cancer, and itis most unlikely that the identical point mutation at codon 282 of thep53 gene would have arisen by chance from separate mutations,especially since codon 282 is not a known "hot spot" for p53mutations.7 It seems probable therefore that the bladder cancerarose as a result of distal tumour cell spread from the primary renalpelvis tumour, rather than there being two tumours arising locallyas independent clones in some sort of "field change". Thisconclusion is also consistent with knowledge that urinary tracttransitional cells are readily shed and that tumour cells can berecovered from urine or bladder washings.Cancer Research Unit,Medical School,University of Newcastle upon Tyne,Newcastle upon Tyne NE2 4HH, UK

J. LUNECC. CHALLEN

Pathology Department,Royal Victoria Infirmary,Newcastle upon Tyne, C. WRIGHT

University Department of Surgeryand Department of Urology,

Freeman Hospital, Newcastle upon Tyne

K. MELLOND. E. NEAL

1. Fujita J, Srivasta SK, Kraus MH, Rhim JS, Tronick SR, Aaronson SA. Frequency ofmolecular alterations affecting ras proto-oncogenes in human urinary tracttumours. Proc Natl Acad Sci USA 1985; 82: 3849-53.

2. Wright C, Mellon K, Neal DE, Johnston P, Corbett IP, Home CHW. Expression ofc-erbB-2 protein product in bladder cancer. Br J Cancer 1990; 62: 764-65.

3. Neal DE, Sharples L, Smith K, Fennelly JA, Hall RR, Harris AL. The epidermalgrowth factor receptor and the prognosis of bladder cancer. Cancer 1990; 65:1619-25.

4. Wright C, Mellon K, Johnston P, et al. Expression of mutant p53, c-erbB-2 and theepidermal growth factor in transitional cell carcinoma of the human urinarybladder. Br J Cancer 1991; 63: 967-70.

5. Yamamoto T, Ikawa S, Akiyama T, et al. Similarity of protein encoded by the humanc-erbB-2 gene to epidermal growth factor receptor. Nature 1986; 319: 230-34.

6. Harris AL. Cancer genes: telling changes of base. Nature 1991; 350: 377-78.7. Levine AJ, Momand J, Finlay CA. The p53 tumour suppressor gene. Nature 1991;

351: 453-55.

8. Sidransky D, von Eschenbach A, Tsai YC, et al. Identification of p53 gene mutationsin bladder cancer and urine samples. Science 1991; 252: 706-08.

Salmonellae from a pet snake and itsbedding

SIR,-over the past 15 months we have been investigating thefood sources in sporadic cases of salmonellosis in Nottinghamshire.Our investigations are based mainly on interview with the patient atthe earliest possible opportunity to obtain a careful dietary history,which is supplemented by sampling and testing of suspect foodswhen possible.A 1-year-old boy had Salmonella typhimurium infection with no

dietary history of suspect foods. On further inquiry we discoveredthat the family kept a pet garter snake which the child handledfrequently, under supervision. We sampled a 1 g piece of woodchipbedding from the snake tank, which was made of glass and heatedwith a lamp. After enrichment culture, well over a hundredpresumptive salmonella colonies were obtained, of which 28 wereanalysed. Although complete serotyping was not attempted, on thebasis of ribotyping analysis we believe that at least 5-7 salmonellatypes were present-including S arizonae (61 % of all isolates), Styphimurium (4%), and S takoradi (25%), which is a rare strainpreviously reported in sludge samples in Verona and Glasgow, andin Italian foxes.

Reptiles carry salmonella, and there is a strong link betweenreptiles and S arizonae in particular, since reptiles were the source ofthe first S arizonae strains characterised.1 In an Israeli survey, 26 of33 (79%) snakes tested carried salmonella, and 77% of these wereS arizonae.2 In a report from Finland, 21 of 25 (84%) reptiles tested

carried salmonella and 61-9% of tested strains were S arizonae.1S arizonae, although not a major food-poisoning strain, has beenimplicated in human illness, especially in immunocompromisedpatients.’We obtained fresh bedding from the pet shop that supplied the

snake and original bedding material. Although this beddingresembled chipped bark whereas the original sample resembledwood shavings, the shop owner claimed that the two beddings camefrom the same source and were of the same quality. This claim wassubstantiated when we again isolated many sahnonellae. Theseisolates were not serotyped, but on the basis of API 20E tests, noS arizonae seemed to be present, indicating that the strains of thisorganism found originally were derived from the snake and notfrom the bedding itself. Similar bedding from a second shopcontained no salmonella.

In addition to the probable contribution of the snake’scommensal flora to the salmonella content of the original sample, aswell as that of the bark bedding, dietary factors might have played apart. Since the snake was fed largely on raw mince, food chain/foodpoisoning strains could also have been introduced into thesalmonella cocktail.We feel that this case shows the potential health hazards

associated with keeping a reptilian pet. The reptile’s naturalintestinal flora, its diet, its bedding, and its contained warmenvironment could combine to produce a thriving population ofpathogenic bacteria.

Department of Applied Biochemistryand Food Science,

Faculty of Agricultural and Food Sciences,University of Nottingham,Loughborough, Leics LE12 5RD, UK

R. A. S. PLUMMERS. J. BLISSETTC. E. R. DODD

1. Greenberg Z, Giladi I, Bouskila A, et al. Salmonella from reptiles in the Arava region,Israel. Isr J Med Sci 1987; 23: 859.

2. Le Minor L. Genus III Salmonella Lignieres 1900, 389AL, In: Krieg N, Hold J, eds.Bergey’s manual for systemic bacteriology, vol 1. Baltimore: Williams and Wilkins,1984.

3. Junttila J, Pajula T, Schildt R. Salmonella in Finnish pets. Suomen Elainlaakarilehti1988; 94: 87-93.

4. Kraus A, Guerra-Batista G, Alarcon-Segovia D. Salmonella arizona arthritis andsepticemia associated with rattlesnake ingestion by patients with connective tissuedisease. A dangerous complication of folk medicine. J Rheumatol 1991; 18:

1328-31.

Litigation over congenital scalp defects

SIR,-Recently I have been approached twice by parents whobelieved that their child’s scalp had been injured during surgicalinduction of labour or by a fetal scalp electrode, and I know of twoother cases. Because some years had passed before medicolegaladvice had been sought (and one child had had plastic surgery) Iasked the parents to identify, from a display of some twenty slides ofscalp defects and injuries, the lesion most resembling that of theirchild’s at birth. They both identified typical aplasia cutis congenita,a condition with an incidence of around 1 in 6000 births, which mostfrequently affects the scalp in the region of the hair swirl. Typically,there is a round, punched-out area about 1 cm across lacking skinand subcutaneous tissues. The surrounding hair may be absent tooor altered in colour. The defect heals by scarring, which is oftenpresent at birth. The pathogenesis is unknown but it is sometimesfamilial or associated with trisomy 13-15. Birth attendants shouldbe aware of this congenital anomaly; neonatal records should becorrectly annotated; and parents should be given a full explanationat the time.

Department of Child Health,University of Bristol,Southmead Hospital,Bristol BS10 5NB, UK PETER M. DUNN

CORRECTION

Cassava cyanogens and konzo, an upper motoneuron disease foundin Africa. -In this article by Dr Tylleskär and colleagues (Jan 25, p 208), theunits for serum thiocyanate in fig 2 should be Nmol/1.