No abstract

Eight polymorphic restriction enzyme sites at the phenylalanine hydroxylase (PAH) locus were analyzed from the parental chromosomes in 33 Danish nuclear families with at least one phenylketonuric (PKU) child. Determination of haplotypes of 66 normal chromosomes and 66 chromosomes bearing mutant allele(s) demonstrated that there are at least two haplotypes which occur predominantly on PKU chromosomes and rarely otherwise. Overall, the relative frequencies of the various haplotypes are significantly different on PKU- and normal-allele bearing chromosomes, even though there is no predominantly occurring unique haplotype which can characterize the PKU chromosomes. In addition, no significant association (linkage disequilibrium) between any single polymorphic site and the mutant allele(s) was observed. The results suggest that either the phenylketonuric mutation was very ancient so that the polymorphic sites and the mutation have reached linkage equilibrium or the mutant allele(s) are the results of multiple mutations in the phenylalanine hydroxylase gene in man. Furthermore, a crude relationship between standardized linkage disequilibria and physical map distances of the polymorphic sites indicates that there is no apparent recombination hot-spot in the human phenylalanine hydroxylase gene, since the recombination rate within the locus appears to be uniform and likely to be occurring at a rate similar to that within the HLA gene cluster. The limitations of this later analysis are discussed in view of the sampling errors of disequilibrium measure used, and the potential utility of the PAH haplotypes for prenatal diagnosis and detection of PKU carriers is established.

Phenylketonuria (PKU) is an autosomal recessive genetic disorder caused by phenylalanine hydroxylase (PAH) deficiency. Individuals afflicted with PKU develop irreversible mental retardation that can be largely prevented by the administration of a low-phenylalanine diet. A number of restriction fragment-length polymorphisms (RFLPs) have been identified in the PAH gene. Combinations of RFLPs constitute unique haplotypes that can be used to identify mutant PAH chromosomes for prenatal diagnostic purpose in PKU families. Unfortunately, the utility of haplotype analysis is limited in populations with a single predominant haplotype. We have identified a novel short tandem repeat (STR) within the PAH gene that has an average level of heterozygosity of about 75% in Orientals and about 80% in European Caucasian populations. This single marker is as informative as haplotype analysis in Europeans and nearly twice as informative as haplotype analysis in Orientals. Although there is statistically significant disequilibrium between STR alleles and RFLP-based haplotypes, there is a relatively low degree of disequilibrium between STR alleles and certain RFLP sites. Nevertheless, the combined use of the STR and RFLP haplotype systems increases the informativity of linkage-based tests for prenatal diagnosis and carrier screening in PKU families.

Foot-and-mouth disease (FMD) is endemic in Bangladesh, and to implement an effective FMD control programme, it is essential to understand the complex epidemiology of the disease. Here, we report on the characterization of FMD virus (FMDV) recovered from FMD outbreaks in Bangladesh in late 2009. All isolated viruses belonged to the FMDV serotype O. The phylogenetic reconstruction showed that all isolates belonged to the Middle East-South Asia (ME-SA) topotype, but fell into two distinct sublineages, one named Ind-2001 (the other has not been named). Within both sublineages, the 2009 Bangladesh isolates were most closely related to viruses from Nepal collected during 2008 and 2009. Additionally, both sublineages contained older viruses from India collected in 2000 and 2001. In South Asia, there is extensive cross-border cattle movement from Nepal and India to Bangladesh. Both these findings have implications for the control of FMD in Bangladesh. Because of the porous borders, a regional FMD control strategy should be developed. Further, animal identification and monitoring animal movements are necessary to identify the cross-border movements and market chain interactions of ruminants, leading to improved border and movement controls. Additionally, a vaccination strategy should be developed with the initial objective of protecting small-scale dairy herds from disease. For any successful FMD control programme, long-term Government commitment and adequate resources are necessary. A sustainable programme will also need farmer education, commitment and financial contributions.

SUMMARY Unprecedented high rates of anthrax outbreaks have been observed recently in cattle and humans in Bangladesh, with 607 human cases in 2010. By enrolling 15 case and 15 control cattle smallholdings in the spatial zone in July-September 2010, we conducted a case-control study, data of which were analysed by matched-pair analysis and multivariable conditional logistic regression. Feeding animals with uprooted and unwashed grass [odds ratio (OR) 41·2, 95% confidence interval (CI) 3·7-458·8, P=0·003], and feeding water hyacinth (Eichhornia crassipes) (OR 22·2, 95% CI 1·2-418·7, P=0·039) were independent risk factors for anthrax in cattle.

Choctaw Native Americans in southeastern Oklahoma have the highest prevalence of scleroderma or systemic sclerosis yet found (469/100,000). An Amerindian HLA DR2 haplotype (DRB1*1602) was significantly associated with scleroderma in this population in a previous study. It is not known, however, if other disease genes are linked to this HLA haplotype. The regions flanking the HLA loci were studied with polymorphic microsatellite markers. An extended HLA DR2 (DRB1*1602, DQA1*0501, DQB1*0301, DPB1*1301) haplotype that includes the class I and III regions was identified which was significantly associated with scleroderma in the Oklahoma Choctaw. No other significant associations with microsatellite marker alleles immediately flanking the HLA region were found.

This paper presents an overview of current knowledge on genetic predisposition to cancer and on enhanced sensitivity of cancer-predisposed genotypes to cancers induced by ionizing radiation. It is intended to provide a background and set the stage for the next papers in this series in which we will assess how such heterogeneity (with respect to predisposition to cancer and presence of radiosensitivity genotypes) in a population may affect estimates of the risk of radiation-induced cancers. The main findings and/or conclusions of the present paper are the following: (1) "Cancer-predisposing genes" (i.e. those at which germinal mutations predispose to cancer) are present in the human genome; these genes are responsible not only for the rare familial cancer syndromes but also for a proportion of the common cancers. At least 21 such genes have now been cloned (including 9 tumor suppressor genes, 11 DNA repair genes and 1 proto-oncogene); further, at least 8 putative tumor suppressor genes and a gene involved in ataxia telangiectasia have been localized to specific chromosomes. (2) These genes play crucial roles in the control of cellular proliferation, programmed cell death (apoptosis) and/or one or another DNA repair pathway. Consequently, mutations in these genes are likely to "liberate" the cells from the normal constraints imposed by them, resulting in unconstrained growth characteristic of cancer. (3) At present, the evidence for increased sensitivity of cancer-predisposed genotypes to radiation-induced cancers is limited. However, current knowledge of the known functions of the cancer-predisposing genes and of the consequences of mutations in these provide (a) sufficient grounds for assuming that the genotypes of those predisposed to cancer may be at an increased risk for radiation-induced cancers and (b) the rationale for attempts to estimate quantitatively the impact of genotype-dependent differences in cancer predisposition and radiosensitivity on cancer risks in an irradiated population.

Individuals genetically predisposed to cancer may be more sensitive to cancers induced by ionizing radiation than those who are not so predisposed. Should this be true, under conditions of radiation exposure, a population consisting of cancer-predisposed and non-predisposed individuals will be expected to respond with a higher total frequency of induced cancers than one in which all the individuals are assumed to have the same sensitivity to radiation-induced cancers. To study this problem quantitatively, we have developed a Mendelian autosomal one-locus, two-allele model; this model assumes that one of the alleles is mutant and the genotypes carrying the mutant allele(s) are cancer-predisposed and are also more sensitive to radiation-induced cancer. Formal analytical predictions as well as numerical illustrations of this model show that: (1) when such heterogeneity with respect to cancer predisposition and radiosensitivity is present in the population, irradiation results in a greater increase in the frequency of induced cancers than when it is absent; (2) this increase is detectable only when the proportion of cancers due to genetic predisposition is large and when the degree of predisposition is considerable; and (3) even when the effect is small, most of the radiation-induced cancers will occur in predisposed individuals. These conclusions are valid for models of cancer when predisposition and radiosensitivity may be either dominant or recessive. The published data on breast cancers in Japanese A-bomb survivors show that at 1 Sv, the radiation-related excess relative risk in women irradiated before age 20 is 13 compared to about 2 for those irradiated at later ages. We examined the application of our model to the above data using two assumptions, namely, that the proportion of cancers due to genetic susceptibility at the BRCA1 locus (1/200) and the frequency of the mutant allele (0.0033) estimated for Western populations are valid for Japanese women. With our model, these results can be explained only if there are very large differences in cancer susceptibility (> 1000-fold) and radiosensitivity (> 100-fold) of the heterozygotes.