Biomedical subjects
Publications and source records attributed to D J Weatherall.
A highly polymorphic DNA probe genetically linked to the locus of autosomal dominant polycystic kidney disease was used in linkage studies for prenatal diagnosis in a nine-week fetus at risk for the disease. The fetus was judged to have inherited the polycystic kidney disease mutation, and this was confirmed by microscopic examination of the fetal kidneys at necropsy.
A survey of the gamma-globin gene region of over 1000 normal individuals revealed a novel 2.5 kb deletion which removes the 5' end of the A gamma-globin gene. Unusually, this deletion in the beta-globin gene cluster is not associated with increased fetal haemoglobin production. Sequence analysis of the deletion endpoints revealed no significant homology at the breakpoint and failed to support a role for a proposed recombination hotspot in IVS-2 in the generation of this illegitimate recombination event. The existence of small "silent" deletions in the beta-globin gene cluster emphasizes the importance of deletion size in altering expression of the fetal globin genes.
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The genetic locus for autosomal dominant adult polycystic kidney disease was recently assigned to chromosome 16 by the finding of genetic linkage to the alpha globin gene cluster. Further study showed that the phosphoglycolate phosphatase locus is also closely linked to both the locus for adult polycystic kidney disease and the alpha globin gene cluster. These findings have important implications for the prenatal and presymptomatic diagnosis of adult polycystic kidney disease and for a better understanding of its pathogenesis.
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We have characterised an unusual, highly polymorphic region of DNA located 8-kb downstream of the human alpha-globin gene complex. This hypervariable region (alpha-globin 3' HVR) is composed of an array of 17-bp tandem repeats, the number of which differs considerably (70-450) from one allele to another. The sequence of the 17-bp repeats is highly conserved within and between alleles. Furthermore, this sequence identifies a core oligonucleotide [5'-GNGGGG(N)ACAG-3'] that is common to three previously characterised hypervariable regions. At reduced stringency, a probe to the 3' HVR detects a new family of multiallelic loci that will be of value in the study of human genetics.
The allele frequency of a Taq 1 gamma-globin gene restriction fragment length polymorphism (RFLP) is reported in ten population groups. In four African populations the 3.0 kb RFLP is common (50/132 beta A chromosomes), whereas it is completely absent in six European/Asian populations (0/277 beta A chromosomes). This Taq 1 RFLP is thus a specific African population marker.
We have studied the mechanism of a transfusion-dependent anaemia found in a two-year-old Maltese girl with visceral leishmaniasis that was resistant to multiple courses of antimonial therapy. Major factors contributing to the anaemia were haemolysis occurring in both the massively enlarged spleen and liver and haemodilution resulting from expansion of the plasma volume. There was no evidence of significant ineffective erythropoiesis, but a reduced plasma iron in the presence of greatly increased iron stores suggested that reticuloendothelial hyperplasia was accompanied by abnormal iron retention by macrophages typical of the 'anaemia of chronic disorders'. This may limit the erythropoietic response to anaemia in chronic visceral leishmaniasis.
A feasibility study of prenatal diagnosis of beta thalassaemia in a northern Italian population has been carried out. Twenty-five families have been studied, each consisting of two parents and a homozygous beta thalassaemia child, thus enabling linkage analysis of restriction fragment length polymorphisms (RFLPs) to the normal and the thalassaemic chromosomes. Using seven standard RFLPs, 19/25 families could be offered prenatal diagnosis; inclusion of the recently described Ava II psi beta polymorphism increased this figure to 23/25 (92%) of the families.
Members of a Cambodian family with an undiagnosed hypochromic, microcytic anaemia were found by haemoglobin and DNA analysis to have five interacting globin gene abnormalities. One child has Hb E and typical Hb H disease, while his mother has the form of Hb H disease associated with Hb Constant Spring interacting with Hb E. Quantitation of Hbs E and A2 by globin chain separation and triton/urea gel electrophoresis support the concept that Hb H/Constant Spring disease is a more severe form of alpha thalassaemia than Hb H disease. This family illustrates how the remarkably high prevalence of globin gene abnormalities in Southeast Asians can give rise to a series of atypical thalassaemic phenotypes, and how they can be defined by direct globin gene analysis.
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Evidence of immune mediated haemolysis was sought in 83 patients with P. falciparum malaria in eastern Thailand. Amongst 73 patients with uncomplicated infection 12 (16.4%) had a weakly positive direct antiglobulin test (DAT). The incidence in 32 children aged 8-16 years was similar to that in adults. Of 10 patients with cerebral malaria, six adults, all of whom were in unrousable coma, had a positive DAT. Erythrocyte-bound IgG1 accounted for the positive DAT in all cases; sensitization with complement or other IgG subclasses was not found. Patients with uncomplicated malaria had a median value of 70 IgG molecules per erythrocyte compared with 65 molecules per cell in 67 healthy controls. This difference was not statistically significant but could account for the lower incidence of a positive DAT in control subjects (4.5%). There was no correlation between the number of IgG molecules per cell and the degree of anaemia during the acute or convalescent phases of the infection. There is no evidence from this study that an immunohaemolytic process contributes to the anaemia of falciparum malaria in eastern Thailand.
Analysis of beta globin gene haplotypes for prenatal diagnosis of beta thalassaemia has revealed a recombination event within the beta globin gene cluster. Both a change in the AvaII polymorphic site within the beta globin gene and a change in the phenotype of the beta globin gene were observed. Paternity was established by the pedigree analysis of hypervariable 'minisatellite' DNA polymorphisms and the most probable explanation of the recombination event is a crossover between the psi beta globin gene and the beta globin gene. The data provide direct evidence in support of a DNA region 3' to the beta globin gene with a recombination frequency much higher than expected, and have important implications for the prenatal diagnosis of beta thalassaemia by linked restriction fragment length polymorphisms.
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alpha Thalassemia modifies the hematologic expression of homozygous sickle cell (SS) disease, resulting in increased total hemoglobin and HbA2 and decreased HbF, mean cell volume, reticulocytes, irreversibly sickled cells, and bilirubin levels. The age at which these changes develop in children with SS disease is unknown. Ascertainment of globin gene status in a large representative sample of children with SS disease has afforded an opportunity to study the hematologic indices in nine children homozygous for alpha thalassemia 2 (two-gene group), 90 children heterozygous for alpha thalassemia 2 (three-gene group), and 167 children with a normal alpha globin gene complement (four-gene group). The two-gene group had significantly lower mean cell volumes from birth, higher red cell counts from one month, lower reticulocytes from three months, and higher HbA2 levels from one year, as compared with the four-gene group. Children with three genes had intermediate indices but resembled more closely the four-gene group. Differences in total hemoglobin or in fetal hemoglobin between the groups were not apparent by eight years of age. The most characteristic differences of the two-gene group were the raised proportional HbA2 level and low mean cell volume, the latter having some predictive value for alpha thalassemia status at birth.
Analysis of DNA from 852 Island Melanesians has revealed a high frequency of single- and triple-gamma-globin genes in this population. Homozygotes for triple- and single-gamma genes have normal hematologic findings, normal hemoglobin F (HbF) levels, and when there is coexisting alpha thalassemia, appropriate levels of Bart's Hb (gamma 4) at birth. In addition, we have identified an individual with a quadruple-gamma gene chromosome who also has a normal HbF level. All single-gamma genes were A gamma, all triple-gamma genes G gamma G gamma A gamma, and the quadruple-gamma gene G gamma G gamma G gamma A gamma. Analysis of G gamma:A gamma ratios in cord bloods and HbF levels in adults showed that these additional gamma genes are expressed and are down regulated appropriately by the fetal to adult Hb switch. Analysis of the restriction enzyme haplotypes of these various chromosomes indicates that intrachromosomal cross-overs are more likely to have produced these variants than interchromosomal recombination events.
The G gamma and A gamma genes of an individual homozygous for the British form of A gamma nondeletion hereditary persistence of fetal hemoglobin have been cloned and partially sequenced. The G gamma gene was normal, but the A gamma gene was found to have a single base change (T----C) at -198 bp relative to the cap site. Supercoiled plasmids containing normal gamma-genes or the mutant A gamma-gene displayed an S1-hypersensitive site immediately 5' to the base change.
The mutation for APKD has previously been localized to chromosome 16 by the demonstration of genetic linkage with both the alpha-chain of hemoglobin and phosphoglycolate phosphatase. These studies were carried out, however, on a limited number of families, and the possibility remained that mutations at other genetic loci might produce the disease. Such genetic heterogeneity of linkage would invalidate the general use of chromosome 16 markers for the purpose of detection of the disease and complicate the characterization of the APKD mutation at the molecular level. Therefore, further families were studied to resolve this issue. A total of 27 Northern European pedigrees were analyzed, all apparently unrelated and with origins in England, Scotland, Holland, and Eastern Finland. No evidence was found to suggest heterogeneity of genetic linkage between alpha-globin and the disease locus in this population.