Sickle Cell Anemia
A number sign is used with this entry because sickle cell anemia is the result of mutant beta globin HBB 141900 in which the mutation causes sickling of hemoglobin rather than reduced amount of beta globin which causes beta-thalassemia. The most common cause of sickle cell anemia is Hb S 141900.0243 , with SS disease being most prevalent in Africans. CLINICAL FEATURES Scriver and Waugh 1930 reported detailed studies of a 7-year old child with sickle cell anemia. Her main complaints were cough,...
134 Synonymous versus nonsynonymous changes
The single base substitutions in coding DNA that result in Hb S and Hb C are examples of non synonymous changes in which a DNA sequence variant results in a change in the RNA codon and alters the encoded protein. In contrast, a synonymous change results in a new codon but not a change in amino acid across the genome such events are the most common variants seen in coding DNA. Within HBB, an example of a synonymous DNA variant is HBB c.33C gt A Fig. 1.23A . With this C to A substitution, the...
133 Transitions versus transversions
Nucleotide substitutions comprise either transversions or transitions Freese 1959 . The A to T substitution responsible for Hb S is an example of a transversion transversions involve substitutions of pyrimidines for purines, or purines for pyrimidines A C, A T, C- G, G- T . In contrast, transitions involve substitution of a pyrimidine for a pyrimidine C for T and vice versa, C T , or a purine for a purine A G . Based on the number of possible combinations, a ratio of 2 1 in the occurrence of...
132 HBB sequence diversity and sickle cell disease
Sequence diversity in the globin cluster plays an important part in the observed clinical heterogeneity in sickle cell disease for affected individuals when an individual inherits the Hb S variant on one allele and a different globin variant on the other. Thus while possessing two copies of Hb S is associated with the most severe disease, having a copy of Hb S combined with a chromosome with a non-functional HBB gene 0 thalassemia may be of comparable severity. Much less severe disease is...
Common And Rare Genetic Variants Associated With Venous Thrombosis 81
remains to be done to resolve remaining genetic determinants. Adopting a non-hypothesis-driven approach based on genome-wide association scans is likely to yield additional variants in potentially unexpected genes whose magnitude of effect may be smaller, but whose importance for our ability to define risk and understand disease pathogenesis is likely to be significant. In the normal physiological state a balance exists between pro-coagulant and anticoagulant mechanisms, allowing extravascular...
Info Vbi
Cystic fibrosis is an autosomal recessive disorder in which specific mutations of the CFTR gene result in dysfunction of epithelial secretion, obstructing ducts in specific organs such as the lung, liver, and bowel. Cystic fibrosis transmembrane conductor regulator CFTR protein functions as a calcium channel and is also involved in regulation of other cellular transport channels. Airway obstruction and chronic bronchopulmonary infection are characteristic of cystic fibrosis, notably persistent...
Aggtaag
Alternative donor site HBA2 exon 1 Figure 1.25 Sequence diversity and alternative splicing. A A variant resulting in p thalassaemia modulates alternative splicing the G to A nucleotide substitution at IVS position 1 in HBB results in two abnormally spliced RNAs HbVar ID 884 HBB c.315 1G gt A OMIM 141900.0348 . B A structural haemoglobin variant, Hb E, in which a G to A substitution activates a cryptic donor site and both mildly reduces p globin synthesis and results in alternative splicing...
Box 116 Beta thalassemia OMIM 141900
The diverse array of sequence variants causing P thalassemia either act to reduce HBB gene expression P type or suppress it completely P0 . A variety of phenotypes are observed with classification into P thalassemia minor, intermedia, and major. Individuals with P thalassemia minor trait have one normal copy of HBB and one affected P0 or P . Such people are usually diagnosed on routine testing with reduced red cell indices. With P thal-assemia intermedia often P P , patients have a significant...
1990
Laws of inheritance with traits passed as distinct discrete entities between generations, with trait variation because inheritable factors Mendel 1865 Nucleic acids isolated Miescher 1869 'Gene' from Greek 'genesis' or 'genos' used to describe determining factor in gamete for a characteritic Johannsen 1909 Linear model of genes on a chromosome 'beads on a string' Morgan 1910 First genetic map Sturtevant 1913 Heredity recognised to have a physical basis - Xrays lead to mutations Muller 1927 -...
123 Sequencing the HBB gene and defining the variant responsible for Hb S
DNA was recognized as the 'heritable material' in 1944 by Avery, Macleod, and McCarty Avery et al. 1944 its double helical structure was elucidated by Watson and Crick in 1953 Watson and Crick 1953 and the nature of the genetic code solved by Nirenberg, Khorana, and Holley in the early 1960s Box 1.9 Fig 1.6 and Fig 1.7 Nirenberg 1963 . The determination of the DNA sequence for the globin genes had its basis in the development of groundbreaking new chemical and enzymatic methods for DNA...