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D R Higgs

Publications and source records attributed to D R Higgs.

At least 109 records · Page 6Linked to original sources
PubMed1988

Individual specific DNA fingerprints from a hypervariable region probe: alpha-globin 3'HVR.

A probe detecting a hypervariable region (HVR) 3' to the alpha globin locus on chromosome 16 has been used to produce DNA fingerprints. Segregation analysis has revealed multiple, randomly dispersed DNA fragments inherited in a Mendelian fashion with minimal allelism and linkage. The fingerprints are highly polymorphic (probability of chance association between random individuals much less than 10(-14]. The probe is, therefore, a powerful discriminating tool: it is envisaged that this probe will have forensic applications, including paternity cases, and will be informative in linkage analysis.

Alleles↗
PubMed1988

Characterization of two deletions that remove the entire human zeta-alpha globin gene complex (- -THAI and - -FIL).

We have fully characterized two alpha thalassaemia mutants that occur in Southeast Asia, - -THAI and - -FIL. Each mutant is due to a deletion that removes the entire zeta-alpha-globin gene complex. Localization of the 5' breakpoints described here, allows the identification of unique fragments that are specific for each of the two mutations. This information can be used to assess the frequency of these mutants in Southeast Asia and will be of value in prenatal testing for alpha thalassaemia in this area.

Child, Preschool↗
PubMed1988

The interaction of alpha thalassaemia and sickle cell-beta zero thalassaemia.

The effects of alpha thalassaemia on sickle cell-beta zero thalassaemia have been studied by comparing haematological and clinical features in four subjects homozygous for alpha thalassaemia 2 (2-gene group), 27 heterozygotes (3-gene group), and 55 with a normal alpha globin gene complement (4-gene group). Alpha thalassaemia was associated with significantly higher haemoglobin levels and lower reticulocyte counts independent of the presence of splenomegaly. Contrary to expectation, alpha thalassaemia was associated with small but significant increases in mean cell volume and mean corpuscular haemoglobin concentration. Splenomegaly at age 5 years and episodes of acute splenic sequestration were significantly more frequent in the 4-gene group. There were no significant differences in painful crises, acute chest syndrome, or other clinical features.

Adolescent↗
PubMed1988

Localisation of human alpha globin to 16p13.3----pter.

A female child with alpha thalassaemia trait, moderate mental retardation, and dysmorphic features has inherited an abnormal chromosome 16 complement as a result of the unbalanced segregation of a maternal balanced translocation. Cytogenetic analysis indicates that the patient is monosomic for 16p13.3----pter and trisomic for 10q26.13----qter. DNA studies show that the patient has not inherited either maternal alpha globin allele. This accounts for the alpha thalassaemia trait in the child and places the human alpha globin complex in band 16p13.3----pter.

Child, Preschool↗
PubMed1988

A new hypervariable marker for the human alpha-globin gene cluster.

We have located a highly polymorphic region of DNA approximately 100 kb upstream of the human alpha-globin genes (the alpha-globin 5' hypervariable region; 5'HVR). The element responsible is a minisatellite sequence comprising a variable copy number tandem repeat array of a G/C-rich 57-bp sequence. This increases the number of minisatellite elements in the vicinity of the alpha-globin genes to five, all of which share a region of sequence identity, thus raising questions concerning the distribution and origins of such tandem repeat sequences. The 5'HVR is highly polymorphic and, together with other hypervariable regions at this locus, provides a valuable genetic marker on the short arm of chromosome 16.

Base Sequence↗
PubMed1988

The polyadenylation site mutation in the alpha-globin gene cluster.

In a previous study, we described a form of nondeletion alpha-thalassemia (alpha T Saudi alpha) found in subjects of Saudi Arabian origin. In the current study, using synthetic oligoprobe hybridization and restriction enzyme analysis, we have demonstrated that the molecular basis of alpha T Saudi alpha is due solely to a single base mutation (AATAAA----AATAAG) in the polyadenylation signal of the alpha 2 gene and that the frameshift mutation in codon 14 of the linked alpha 1 gene is the result of a cloning artefact. The alpha 2 polyadenylation signal mutation occurs in other Middle Eastern and the Mediterranean populations and is responsible for the clinical phenotype of Hb H disease in some Saudi Arabian individuals with five alpha genes (alpha T Saudi alpha/(alpha alpha alpha)T Saudi). Evidence suggests that the (alpha alpha alpha)T Saudi haplotype has arisen as a result of a recombination between two misaligned chromosomes bearing the alpha T Saudi alpha defect.

Alleles↗
PubMed1987

Unusual features of CpG-rich (HTF) islands in the human alpha globin complex: association with non-functional pseudogenes and presence within the 3' portion of the zeta gene.

We have characterised a cluster of CpG rich (HTF) islands in the alpha-globin complex and report here two unusual features: The human embryonic zeta 2-globin gene is associated with an HTF island within its 3' portion rather than at the 5' end. Furthermore at least two non-functional pseudogenes within the cluster (psi zeta 1 and psi alpha 2) are associated with CpG rich islands.

Animals↗
PubMed1987

Long range genome structure around the human alpha-globin complex analysed by PFGE.

A map encompassing 300 kilobases (kb) in and around the human alpha-globin gene complex shows features with important implications for understanding the structure and function of the human genome. In contrast to other segments of the mammalian genome that have been analysed by pulsed field gradient electrophoresis (PFGE), this region contains an unusually high density of sites for infrequently cutting restriction enzymes that recognise GC rich motifs including the under-represented CpG doublet. This suggests that the 26 kilobase (kb) stretch of DNA containing the alpha-globin gene family, which is known from sequence analysis to be 60% GC rich, is itself embedded within a region of high GC content. This long-range structure, identified by PFGE, corresponds to a class of GC rich isochores that are thought to represent early replicating DNA present in Giemsa negative chromosomal bands. The identification of such regions by PFGE will be of value in understanding the organisation of human chromosomes and will influence the strategies used to construct a physical map of the genome.

Base Composition↗
PubMed1987

Recombination at the human alpha-globin gene cluster: sequence features and topological constraints.

We have characterized 170 kb of DNA around the human alpha-globin gene cluster to enable a systematic analysis of 12 naturally occurring deletions from this region. In 8 deletions, the 3' breakpoints lie within a 6-8 kb segment of DNA, identifying a breakpoint cluster region. Members of the Alu family of repetitive sequences are frequently found at the breakpoints and we describe a novel deletion due to homologous recombination between such repeats. In another deletion the breakpoints are separated by 131 bp of DNA, which we have shown to be transposed from a region 36 kb upstream from the 5' breakpoint where it is present in the inverse orientation. The sizes of these deletions, the nonrandom distribution of their breakpoints, and the nature of the inversion-duplication transposition event suggest that these rearrangements are constrained by the higher-order structure of the alpha-globin cluster.

Base Sequence↗
PubMed1987

Non-methylated CpG-rich islands at the human alpha-globin locus: implications for evolution of the alpha-globin pseudogene.

We have analysed CpG frequency and CpG methylation across part of the human alpha-globin locus. Clusters of CpG at the alpha 1 and alpha 2 genes resemble the 'HpaII tiny fragment (HTF) islands' that are characteristic of mammalian 'housekeeping' genes: CpG frequency is not suppressed; testable CpGs are not methylated in DNA from erythroid or nonerythroid tissues, although flanking CpGs are methylated; CpG clusters are approximately 1.5 kb long and extend both upstream and downstream of the alpha-globin transcription start site. These features are not found at genes of the beta-globin locus. The alpha-globin pseudogene (psi alpha 1) is highly homologous to the alpha 2 and alpha 1 genes, but it lacks an HTF island. Sequence comparison shows that a high proportion of CpGs in the alpha 2 gene are substituted by TpG or CpA in the pseudogene. This strongly suggests that an ancestral HTF island at the pseudogene became methylated in the germline, and was lost due to the mutability of 5-methylcytosine.

Base Sequence↗
PubMed1987

Allele-specific DNA identity patterns.

A method of genetic analysis is presented which involves digestion of DNA with a single restriction enzyme (PvuII) and hybridisation with a mixture of five probes. Four of the five probes chosen recognise hypervariable regions (HVRs) of the human genome and hence an allele-specific DNA identity pattern results. An advantage of this approach to genetic characterisation is that the complex identity patterns may be broken down into simple allelic systems of known chromosomal localization by hybridisation with the individual probes. Also different probes may be included in a combined probe designed for particular types of investigation.

DNA Restriction Enzymes↗
PubMed1987

Characterization of a new alpha zero thalassaemia defect in the South African population.

A new alpha thalassemia defect has been detected in the South African population. Restriction mapping of the alpha globin gene cluster in affected individuals has established that the defect is associated with the removal of 22.8-23.7 kb of DNA, including the psi zeta 1, psi alpha 1, psi alpha 2, alpha 2 and alpha 1 globin genes. The 5' endpoint of the deletion has been localized between the zeta 2 and psi zeta 1 globin genes, and the 3' endpoint lies 4-5 kb 3' to the alpha 1 globin gene. We have called the deletion - -SA in order to distinguish it from alpha zero thalassaemia defects described in other populations.

Chromosome Deletion↗
PubMed1987

Alpha-thalassaemia in Nigeria: its interaction with sickle-cell disease.

We have determined the molecular basis and frequency of alpha-thalassaemia in Nigeria. The alpha-thalassaemia determinant in this population is caused by only one type of single alpha globin gene deletion (-alpha 3.7). Comparison of the haematological features of those patients who have sickle-cell disease with (-alpha/alpha alpha, -alpha/-alpha) or without (alpha alpha/alpha alpha) alpha-thalassaemia showed similar trends to those reported in Jamaican and U.S. patients with these interactions. However, in contrast to studies in some other African populations we have shown that the frequency of alpha-thalassaemia in Nigeria is the same (0.24) in patients with or without homozygous sickle-cell disease (AA, AS and AC genotypes).

Adolescent↗
PubMed1987

High resolution gene mapping of the human alpha globin locus.

A combination of polymorphic DNA markers, cytogenetic analysis, and in situ hybridisation has been used for the high resolution assignment of the human alpha globin gene cluster on chromosome 16. Multiallelic DNA probes from within the alpha globin cluster were used to determine the number of copies of this locus in three cell lines containing trisomies of the short arm of chromosome 16 and one with a familial inversion, inv(16). The breakpoints in these rearrangements flank the alpha globin locus and locate a shortest region of overlap to 16p13.1. A meiotic crossover was also localised to this band. In situ hybridisation of biotinylated DNA probes to normal and inverted chromosomes 16 [inv(16)(p13.1;q22)] showed hybridisation sites at opposite ends of the chromosomes, consistent with this regional localisation.

Chromosome Inversion↗
PubMed1987

Different hematologic phenotypes are associated with the leftward (-alpha 4.2) and rightward (-alpha 3.7) alpha+-thalassemia deletions.

We have compared the phenotypes of the two common deletion forms of alpha+-thalassemia by analysis of umbilical cord blood samples from Melanesia. Homozygotes for the leftward, 4.2-kilobase, deletion (-alpha 4.2) had significantly higher levels of Hb Bart's at birth than homozygotes for the rightward, 3.7-kilobase, deletion (-alpha 3.7). Compound heterozygotes for each deletion had intermediate values. Although deletion forms of alpha 0 thalassemia were not found in this survey, nondeletion alpha-thalassemia was present at low frequency. Since the predominant rightward deletion in this population, -alpha 3.7III, entirely removes the alpha 1-gene and the 4.2-kilobase deletion deletes the alpha 2-gene, these data indicate that the alpha 2-globin gene has a higher output than the alpha 1-gene, on single alpha-gene chromosomes.

Chromosome Deletion↗
PubMed1987

The cellular basis for different fetal hemoglobin levels among sickle cell individuals with two, three, and four alpha-globin genes.

Fetal hemoglobin (HbF) levels vary widely among individuals with sickle cell anemia (SS). Previous studies have suggested that HbF levels in SS individuals with alpha-thalassemia (two or three functional alpha-globin genes) are lower than HbF levels in SS individuals with four normal alpha-globin genes. Using immunocytochemical techniques, we studied F cell production as measured by % F reticulocytes, the amount of HbF per F cell, and the preferential survival of F cells versus non-F cells in 51 subjects with four alpha genes, 32 subjects with three alpha genes, and 18 subjects with two alpha genes. Comparison between alpha-globin gene groups was performed for the total sample as well as for a subset of 82 individuals who had replicate samples and a further subset of 39 age-matched individuals. %HbF levels were 6.8, 4.9, and 4.5 percent for the total four-, three-, and two-alpha-globin-gene groups, respectively. The percentage of F reticulocytes, percentage HbF per F cell, and the enrichment ratio (% F cell/% F reticulocytes) did not change significantly with alpha-globin gene number. Moreover, no correlation existed between alpha-globin gene number and the absolute number of F cells in any group studied. However, there was a strong inverse correlation (r = -0.407, P = .0001) between non-F cell levels (1.7 +/- 2, 2.2 +/- 5, 3.0 +/- 1.0 X 10(12)/L) and decreasing alpha-globin gene number. These data suggest that falling HbF levels among SS individuals with lessened numbers of alpha-globin genes reflect prolonged survival of non-F cells and are not due to intrinsic differences in F cell production or in the amount of HbF per F cell. The improved survival of non-F cells in SS alpha-thalassemia is presumed to be due to the lower MCHC observed in such individuals.

Anemia, Sickle Cell↗