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Biomedical subjects

L Pressley

Publications and source records attributed to L Pressley.

27 records · Page 2Linked to original sources
PubMed1980

A novel alpha-globin gene arrangement in man.

The human genome has two linked alpha-globin genes on chromosome 16. Deletion of one or more of them, as occurs in alpha-thalassaemia, leads to a reduced output of alpha-globin mRNA in proportion to the number of alpha-globin genes lost. In some racial groups deletion of one of the pair of alpha-globin genes may result from unequal crossing over between the genes on homologous chromosomes by a mechanism resembling that postulated for the formation of the delta beta fusion genes of the Lepore haemoglobins. By analogy, the opposite chromosome in this cross-over should have three alpha-globin genes just as the 'anti-Lepore chromosome has three non-alpha chain genes. We describe here a Welsh family in which three members have five alpha-globn increased alpha mRNA output and it may therefore produce the phenotype of mild beta-thalassaemia.

DNA Restriction Enzymes↗
PubMed1980

Gene deletions in alpha thalassemia prove that the 5' zeta locus is functional.

The deletions in the zeta-alpha globin gene cluster in two infants with the hemoglobin Bart's hydrops fetalis syndrome (homozygous alpha thalassemia 1) have been mapped by restriction endonuclease analysis using a zeta-specific probe. DNA from a Thai infant lacked the psi alpha 1 gene and both alpha genes, but the zeta genes were present. A Greek infant's DNA had also lost the 3' zeta 1 gene. Because zeta globin was synthesized in the infant's cord blood, this indicates that the 5' zeta 2 gene recently identified by Lauer et al. [Lauer, J., Shen, C. J. & Maniatis, T. (1980) Cell, in press] must be functional.

Chromosome Deletion↗
PubMed1980

Detection of alpha thalassaemia in Negro infants.

A prospective study of 2191 Negro infants in Jamaica showed that approximately 7% of them had detectable levels of Hb Bart's (gamma 4) in the neonatal period. The red cell indices, globin chain biosynthesis and restriction endonuclease mapping of DNA from these infants were used to determine the significance of Hb Bart's at birth. The results indicate that the genotypes alpha alpha/alpha alpha, -- alpha/alpha alpha and -- alpha/ -- alpha are associated with 0%, 0.1-2%, and greater than 2% Hb Bart's respectively. Although trace amounts of Hb Bart's may be associated with the genotype -- alpha/alpha alpha this is not always the case and therefore haemoglobin analysis in the neonatal period cannot be used to diagnose this genotype with any certainty.

Black People↗
PubMed1980

The genetic basis of Hb Q-H disease.

A Chinese family has been studied in which two siblings have haemoglobin Q-H disease. Using a combination of haematological and haemoglobin analysis, globin chain synthesis, analysis of alpha/beta globin messenger RNA ratios and restriction endonuclease mapping, it has been shown that each of these siblings has received one chromosome on which both alpha chain genes have been deleted and another on which there is only a single alpha chain locus which carries the alpha Q mutation. Their genotype is thus --/-alpha Q. Despite the fact that the haemoglobin Q mutation in this family is carried on a chromosome with a single alpha chain locus, heterozygous carriers for the variant have only 25% or less haemoglobin Q. Our observations indicate that the molecular basis for haemoglobin Q-alpha thalassaemia is similar to that for the common form of haemoglobin H disease in Orientals. Furthermore, they provide clear evidence that the level of an alpha chain variant in heterozygous carriers is not a reliable reflection of the number of alpha globin genes.

Aged↗
PubMed1980

alpha thalassemia in black populations.

The different alpha thalassemia genotypes in American and Jamaican black populations have been defined by hematologic and globin-chain synthesis studies, alpha/beta globin messenger RNA ratios and restriction endonuclease mapping of DNA. The results indicate that the common form of alpha thalassemia in these populations is the deletion type of alpha-thalassemia 2 (- alpha/alpha alpha). The homozygous state (- alpha/alpha- alpha) is expressed at birth by the presence of more than 2--3% hemoglobin Bart's; in adult life it has the same phenotype as the heterozygous state for the deletion form of alpha-thalassemia 1 (--/alpha alpha). The heterozygous state is not always associated with detectable amounts of hemoglobin Bart's at birth or with recognizable hematologic changes in adults.

Black People↗
PubMed1979

Negro alpha-thalassaemia is caused by deletion of a single alpha-globin gene.

Studies in two Jamaican Negro families, including haematological and haemoglobin analysis, haemoglobin synthesis, and globin messenger-RNA assay, have defined two alpha-thalassaemia phenotypes which resemble the severe (alpha-thalassaemia 1) and mild (alpha-thalassaemia 2) forms of the disorder described in Orientals. Genetic analysis suggests that subjects with the alpha-thalassaemia-1 phenotype are homozygous for the alpha-thalassaemia-2 determinant. Restriction-endonuclease mapping shows that alpha-thalassaemia-2 results from the deletion of one of the linked pair of alpha-chain genes. Hence the genotypes of the alpha-thalassaemia heterozygotes and homozygotes in these families are -alpha/alpha alpha and -alpha/-alpha respectively. If these are the usual alpha-thalassaemia genotypes in Negroes, these findings explain the difference in clinical expression of the disorder between Orientals and Negroes--in particular, the absence of haemoglobin Bart's hydrops and the rarity of haemoglobin-H disease in Negroes.

Black People↗
PubMed1975

Glucocorticoid and mineralocorticoid receptors in gut mucosa.

Both glucocorticoid and mineralocorticoid hormones are known to be involved in the physiology and pathophysiology of the gastrointestinal tract. Studies on the mechanism of action of steroid hormones indicate an initial obligatory step of binding to stereospecific receptor proteins in the cytoplasm of target tissue cells. Mucosal cells from the gastrointestinal tract of adrenalectomized, gonadectomized rats contain cytoplasmic glucocorticoid receptors which bind tritiated dexamethasone with an affinity (Kdiss4C) of approximately 10(-8)M. The concentration of glucocorticoid receptors per unit cytoplasmic protein is in order duodenum greater than jejunum greater than ileum=stomach greater than colon, and their affinity for steroid hormones is in order dexamethasone greater than corticosterone greater than deoxycorticosterone=aldosterone. No glucocorticoid receptors could be demonstrated in esophageal mucosal cells. Binding sites for tritiated aldosterone, with affinity characteristics appropriate for physiological mineralocorticoid receptors, were demonstrated in duodenum, jejunum, ileum and colon. No similar sites could be shown in the mucosa of the gastric antrum.

Aldosterone↗