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Haematological disorders
Published in Judy Bothamley, Maureen Boyle, Medical Conditions Affecting Pregnancy and Childbirth, 2020
Most of the haemoglobin found in healthy adults is termed Hb A and contains two alpha chains and two beta chains, but there are other types. Fetal haemoglobin (Hb F) contains a pair of alpha chains but in place of the beta chains, it contains a pair of gamma chains. Fetal haemoglobin has enhanced oxygen trapping capabilities useful for intra-uterine life and levels decrease to a minimum by six months of age. There is also Hb A2, a minority adult haemoglobin (see Box 6.6).
Haematological disorders
Published in Judy Bothamley, Maureen Boyle, Medical Conditions Affecting Pregnancy and Childbirth, 2020
Most of the haemoglobin found in healthy adults is termed HbA and contains two alpha chains and two beta chains, but there are other types. Fetal haemoglobin (HbF) contains a pair of alpha chains, but in place of the beta chains, it contains a pair of gamma chains. Fetal haemoglobin has enhanced oxygen-trapping capabilities useful for intra-uterine life and levels decrease to a minimum by six months of age. There is also HbA2, a minority adult haemoglobin (seeBox 4.7).
Biochemical Aspects of Fatty Liver
Published in Robert G. Meeks, Steadman D. Harrison, Richard J. Bull, Hepatotoxicology, 2020
The connection between the lipid-containing vesicles, or liposomes, (Baglio and Farber, 1965) and the plasma membrane is done by microtubules. Their main protein, tubulin, is a macromolecule resulting from polymerization of several subunits. These are heterodimers formed by two different chains, usually referred to as alpha and beta chains. The alpha chains contain a site that is able to bind to colchicine, as well as another to bind to podophyllotoxin. It is connected to the beta chain by a GDP molecule.
Phenotypic variation in sickle cell disease: the role of beta globin haplotype, alpha thalassemia, and fetal hemoglobin in HbSS
Published in Expert Review of Hematology, 2022
This covers a variety of conditions varying in hematology and clinical features largely determined by the molecular mutation of the beta thalassemia gene. Broadly, there are two major phenotypes, depending on the amount of normal beta chain and hence HbA produced, sickle cell-beta+ thalassemia and sickle cell-betao thalassemia. The molecular mutations for beta thalassemia vary geographically (Table 1), and differ widely between continents and even between different areas of a small Island such as Jamaica where differences occur in communities only 100 km apart [9]. In Table 1, the Jamaican data derive from the screening of 100,000 newborns at Victoria Jubilee Hospital between 1973–1981 [6] and from the Manchester Project in central Jamaica, which offered free genotype detection to 16,612 senior school students between 2008 and 2013 [9]. Indian data derive from 5,615 subjects with the beta thalassemia trait between 2001 and 2015 studied at the National Institute of Immunohaematology in Mumbai [10].
Beta-cell failure in type 2 diabetes: mechanisms, markers, and clinical implications
Published in Postgraduate Medicine, 2020
When beta cells produce insulin, it is first secreted as proinsulin. C-peptide is a 31-amino acid polypeptide that connects the alpha and beta chains of proinsulin [58]. Upon removal of C-peptide from the proinsulin molecule, the alpha and beta chains become linked, and proinsulin turns into insulin. Thus, C-peptide and insulin are present in beta cells in equal amounts and are co-secreted into the portal vein in equimolar amounts. In contrast to insulin, C-peptide does not undergo hepatic degradation and is cleared entirely in peripheral tissues at a relatively constant rate. C-peptide has a substantially longer half-life than insulin (approximately 35 min vs. 3–5 min) [59,60]. Furthermore, in individuals who are receiving insulin therapy, insulin assays cannot distinguish endogenous and exogenous insulin, but the differential kinetics of C-peptide mean that peripheral plasma C-peptide concentrations can be used to accurately estimate insulin secretion.
Fetal hydrops – a review and a clinical approach to identifying the cause
Published in Expert Opinion on Orphan Drugs, 2020
Esther Dempsey, Tessa Homfray, John M Simpson, Steve Jeffery, Sahar Mansour, Pia Ostergaard
Alpha thalassemia is caused by mutations in the alpha-globin genes leading to a reduction or absence of their product: alpha-globin. The normal adult state is to have two alpha-globin genes tandemly encoded (in cis) on each of an individual’s two chromosome 16 (i.e. 4 alpha-globin genes in total). During the embryonic stage the alpha-like globin, sigma-globin, forms a tetramer with two epsilon-globin chains. During the 6th week of gestation, erythropoiesis becomes a primary function of the fetal liver (rather than yolk sac) and fetal hemoglobin consisting of two alpha and two gamma-globulin chains is produced [38]. If a baby inherits a chromosome 16 with the alpha-globin genes deleted or has a pathogenic mutation in both alpha chains (–/–) from each parent, hemoglobin tetramers assembled will consist entirely of beta chains. This results in Hb-Barts (homozygous alpha-thalassemia), which normally results in fetal loss (anemia, hypoxia and nonimmune fetal hydrops) in the third trimester [39]. Rarely, HbH disease (–/-a) has been identified as a cause of fetal hydrops [40].