Maternal segregation distortion in sickle-cell trait

Italy,

and suggests that some unfavourable changes in the of the disease may have been introduced.

treatment

Supported by the Italian National Research Council ACRO Applied Project, and by the Italian Association for Cancer Research. *Carlo La Vecchia, Eva

Negri,

Adriano Decarli

*Istituto di Ricerche Farmacologiche "Mario Negri", 20157 Milan, Italy; and Istituto di Statistica Medica e Biometria, Università degli Studi di Milano,

Milan, Italy

1 2

3 4

La Vecchia C, Decarli A. Trends in childhood cancer mortality in Italy. Tumori 1985; 71: 111-17. LaVecchia C, Decarli A. Decline of childhood cancer mortality in Italy, 1955-1980. Oncology 1988; 45: 93-97. La Vecchia C, Negri E, Decarli A. Childhood cancer mortality in Italy. Rev Epidém et Santé Publ 1994; 43: 383-84. Parkin DM, Clayton D, Black RJ, et al. Childhood leukaemia in Europe after Chernobyl: 5 year follow-up. Br J Cancer 1996; 73: 1006-12.

depressive disorder and control individuals (3-9 vs 4-8%). There was also no significant differences in the frequency of transmitted versus non-transmitted TR genotypes or alleles for manic-depressive disorder (table). These results offer no support for the involvement of tyrosine hydroxylase in familial manic-depressive illness in a North American population. For the odds ratios of 2-4-4-2 noted by Meloni et al’ and Leboyer et al,2 the current casecontrol and haplotype relative risk analyses have greater than 90% to detect associations between these power and polymorphisms manic-depressive illness. Undetected population stratification in case-control analyses or true population differences may account for these conflicting findings. Other member of the working group include Janice M Hickok, Alana Walczak, Alan Yam, and Theodore Reich (Washington University School of Medicine, St Louis).

*Richard D Todd, Elizabeth A Lobos, Abbas Parsian, Sylvia Simpson, J Raymond DePaulo, for the Bipolar Disorder

Manic-depressive illness hydroxylase markers

and

tyrosine

SiR-Most case-control and linkage studies have reported negative results for the association of tyrosine hydroxylase with manic-depressive illness. However, Meloni et al’ and et aF reported positive associations in cases and controls of French origin. In particular, they reported a decreased frequency of allele C and an increased prevalence of the BE genotype for a tetranucleotide repeat polymorphism which was clinically associated with a family history of manic-depressive illness.’ Because case-control designs are sensitive to population stratification, several authors have proposed the use of haplotype relative risk designs in which patients and their parents are genotyped.3 Frequencies of transmitted and non-transmitted alleles or genotypes, which are necessarily from the same parental

Working Group Departments of *Psychiatry and Genetics, Washington University School of Medicine, St Louis, MO 63110-1093, USA; and Department of Psychiatry, Johns Hopkins School of Medicine, Baltimore, Maryland

1

Meloni

2

Lancet 1995; 345: 932. Leboyer M, Malafosse A, Boularand S, et al. Tyrosine hydroxylase polymorphisms associated with manic-depressive illness. Lancet 1990;

Leboyer

gene

pool,

are

335:1219. 3

4

5

Schaid DJ, Sommer SS. Comparison of statistics for candidate gene association studies using cases and parents. Am J Hum Genet 1994; 55: 402-09. Todd RD, O’Malley KL. Population frequencies of tyrosine hydroxylase RFLPs in bipolar affective disorder. Biol Psychiatry 1989; 25: 626-30. Roff DA, Bentzen P. The statistical analysis of mitochondrial DNA polymorphisms: chi-square and the problem of small samples. Mol Biol Evol 1989; 6: 539-43.

compared.

To test for the presence of the associations reported by Meloni et al’ and Leboyer et aF in a North American population, the probands of multiple incidence manicdepressive disorder or alcoholism pedigrees meeting DSMIII-R diagnostic criteria were studied. Controls were selected to be older than patients, and to have no personal or family history of affective illness, alcoholism, or psychosis. All participants were non-hispanic whites. 76 (mean 37 [SD 12] years, 62% women) had manic-depressive disorder; 120 had alcoholism (mean 41 [11], 22% women); and 83 controls were selected (50 [8] years, 48% women). Both parents were available for 51 manic-depressive disorder patients. Genomic DNAs were typed for three restriction fragment length polymorphisms2,4 (RsaI, TaqI, and BgIII) and for the intron 1 tetranucleotide repeat polymorphism’ (TR) of the tyrosine hydroxylase gene. Significance values for X2 tests with small cell sizes were estimated with Monte Carlo simulation. Genotype frequencies for all polymorphisms were in Hardy-Weinberg equilibrium for all groups and there were no within-group sex differences. There were no significant differences in genotype or allele frequencies among the three contrast groups at any locus. The prevalence of the TR-BE genotype was similar in manic-

49 of 51 matings were informative. Table: Frequency of transmitted alleles

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R, Leboyer M, Bellivier F, et al. Association of manicdepressive illness with tyrosine hydroxylase microsatellite marker.

versus

non-transmitted TR

Maternal trait

segregation distortion

in sickle-cell

SiR-Silva and Ramalho (March 9, p 691)’report from nonmalarial Brazil their study of nuclear families, 163 of whom had one parent with sickle-cell trait (Hb AS) and 86 had one parent with p-thalassaemia minor. They claim that substantial maternal segregation distortion favoured the transmission of S-haemoglobin and p-thalassaemia alleles, and contributed to maintaining these polymorphisms. This suggestion is not in accord with our observations in the population of Garki in the Sudan savanna of Nigeria, where malaria is hyperendemic.2 The distribution of genotypes in 534 infants, born during 3 years into an initial population of 2742, was close to and did not differ significantly from that expected from gene frequencies (A 0-850, S 0-146, C 0-004), following the Hardy-Weinburg law (table): no excess Hb AS was recorded in newborn babies. There was an increase of the proportion with sickle-cell trait, from 23-6% at birth to about 29% in all age groups over 5 years. The greater genetic fitness ratio3 of the Hb AS (1-206) was accounted for by a differential survival (1-290) compared with Hb AA. The fertility of women with sickle-cell trait (147-8 per 1000 per year) did not differ significantly from that of women with only adult haemoglobin (153-3 per 1000 per year). Better survival could be explained by a partial protection against intense Plasmodium falciparum parasitaemia from 30 weeks of age and into early childhood.

in human and veterinary practice should be involved. The crisis is too important to be left to the experts.

practitioners

*John S S Stewart,

Bryan Jeffrey

*74 The Common, Parbold, Chorley, UK

1

2 Goodness of fit X2 -test, observed vs expected: *p<0001, tp>O.9. Table: Haemoglobin electrophoretic patterns in whole and newborn populations in Garki, northern Nigeria, compared with distributions expected from Hardy-Weinberg law

Wigan

WN8 7EA, UK; and Knowles Farm, Withnell,

Brown P. Bovine spongiform encephalopathy and Creutzfeldt-Jakob disease. BMJ 1996; 312: 970-71. Anon. Less beef, more brain. Lancet 1996; 347: 915.

SiR-Ramsay reported (March 30, p 889)’ that the Spongiform Encephalopathy Advisory Committee (SEAC) maintains that "infants and children are not likely to be more to that infection than adults". I would be interested to know the evidence for such advice. Apart from disease related to ageing, infants and children, unless immunised, are in general at greater risk of infection than adults. Early infancy is a sensitive period for the establishment of an allergic reaction to a protein in the diet. Even within the population of infants and children there are likely to be differences in susceptibility depending on feeding history. Bottle-fed children are at greater risk of gastrointestinal infections compared with breast-fed babies. Not only is breast milk immunoprotective but also it contains factors that stimulate proper intestinal development. Improper development of the gastrointestinal tract is likely to risk proteins crossing into the blood stream intact. Proteins that could cause disorders such as BSE would more readily cross the gastrointestinal barrier in infants.

susceptible

Greater chances of survival for children with Hb AS was sufficient alone to maintain the high S gene frequency in Garki, and we saw no evidence of (i) a high rate of mutation; (ii) increased fertility in women with sickle-cell trait; or (iii) maternal (or paternal) segregation distortion favouring transmission of the gene. It is not easy to accept mechanisms of segregation distortion that operate only in populations not exposed to malaria. Alan F

Fleming

Laboratory Services, University Teaching Hospital, Private Bag RW 1X, Ridgeway 15102, Lusaka, Zambia

1 Silva ID, Ramalho AS. Maternal segregation distortion in sickle-cell and B-thalassaemia traits? Lancet 1996; 347: 691-92. 2 Fleming AF, Storey J, Molineaux L, et al. Abnormal haemoglobins in the Sudan savanna of Nigeria, I: prevalence of haemoglobins and relationships between sickle-cell trait, malaria and survival. Ann Trop Med Parasitol 1979; 73: 161-72. 3 Cavalli-Sforza L, Bodmer W. The genetics of human populations. San Francisco: Freeman, 1971: 137. 4 Rucknagel DL, Neel JV. The hemoglobinopathies. In: Steinberg G, ed. Progress in medical genetics. New York: Grune and Stratton, 1961: 158-260.

Michael Crawford Queen Elizabeth Hospital for Children, London E2 8PS, UK

1

Ramsay S. Advice causes concern

Prion Beef safety and information

publication of scientific

SIR-The link between bovine spongiform encephalopathy (BSE) and a new variant of Creutzfeldt-Jakob Disease (CJD) from eating beef is unproven.’ The European export ban on British beef has been widely interpreted as political rather than scientific. The UK government appears to be inconsistent when it agrees to a slaughter policy while insisting that beef is safe to eat. The government says that scientific advice has always been accepted. The main problem, as you rightly emphasise, is that scientific evidence has not been made publicly available and that expert committees, appointed by ministers, meet in private. A letter to the Minister of Agriculture elicited a response from his private office giving some unpublished results of the pathogenesis experiment being conducted by the Central Veterinary Laboratory. Infectivity can be detected in the intestine of experimentally exposed animals at a stage when no clinical symptoms have emerged and where there is no brain histology indicative of disease and indeed no infectivity in the brain. Brain infectivity develops later when infectivity is no longer detectable in the intestine. How this affects slaughter policy is not entirely clear but it should be a matter for informed public debate in the light of the scientific evidence. The credibility of government policy can be restored only by publication of evidence which has already been placed before their own expert committee. The restoration of confidence is important, so general as well as specialist

over

safety of British beef.

Lancet

1996; 347: 889.

protein

released

by platelets

SIR-The host-cell type involved in prion uptake and transport to the nervous system in prion protein (PrP) diseases is not known. A vascular variant of prion protein amyloidosis has been described suggesting that PrP may derive from the circulation’ and since platelets share some biochemical and morphological characteristics with neurons2 we looked for Prpc in circulating human platelets. Fresh platelets were purified by gel filtration3and the purity of the isolate was ascertained by light microscopy. Platelet aliquots were incubated with PIPLC or collagen. PrP is bound to the cell surface by a GPI-anchor and PIPLC is an enzyme that specifically releases proteins from this anchor. Collagen is a platelet agonist that induces platelet aggregation and secretion. SDS-PAGE of platelet releasates

analysed by western blot with 3F4, a monoclonal antibody that recognises an epitope comprising human PrP residues 109-112. Immunoblot analysis of releasates showed a major band of 35-40 kDa for both PIPLC and collagen stimulated platelets (figure). The immunoreactivity of the bands disappeared after adsorption of antibody activity with the PrP synthetic peptide 102-114. As a control for secretion we tested the releasate of collagen-stimulated platelet for the presence of apolipoprotein J, a platelet-secreted protein, with an affinity-purified polyclonal antibody. To monitor lysis, all releasates were tested for the absence of actin, a platelet cytoskeletal non-secretory protein, with a monoclonal antibody to actin. These results indicate that platelets express PrP% the sixth GPI-anchored platelet protein to be described, and that they shed this normal soluble protein on agonist stimulation. It were

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