L15 and L16 Sickle Cell Anaemia Flashcards
Haemoglobinopathies
Diseases of Hb
Human Globin Gene Clusters
See onenote
- alpha globin clusters
- beta globin clusters
Formation of Hb fusion genes
see onenote slides
- occur via unequal crossovers
- Give rise to certain types of Hb which are disease Hb
Sickle Cell Anaemia
HbS
- balanced polymorphism
- malaria, selective pressure of sickle cell anaemia
Sickle beta globin mutation
see onenote slides
Codon change
- Glutamate => Valine
- Negatively charged => positively charged
- Molecule folds differently due to change of charge
Granula appearance - fibres of sickle cell that have precipitated within the cell
- Characteristic to SCA
- Sickling appearance is the selective pressure, advantageous against malaria, malaria parasites can’t grow in these types of cells
From genotype to phenotype is sickle cell anaemia
see onenote slides and diagram
Quantitative abnormalities of Hb
see onenote
alpha thalassaemia
- deficiency of alpha globin chains
beta thalassaemia
- deficiency of beta globin chains
HPFH
- hereditary presistence of fetal Hb (usually no symptoms)
Malaria provides selective pressure for thalassemia alleles and HbS
Thalassaemia features
see onenote
Expansion of the skull
- A lot of Hb
- Very little normal Hb, body tries to make more Hb to compensate
Blood transfusions in developing countries
- Contaminated blood with HIV
- Couldn’t afford
Linkage disequilibrium
see onenote
- alleles at separate loci associated with each at a higher frequency than is expected by chance
- LD strong evidence that a locus lies in a small, defined chromosomal region
- LD occurs for HbS and Thal alleles
Schematic of human beta globin gene
see onenote
illustrates possibilities for altered expression
Phenotype of RBC - normal, alpha-thal, beta-thal
see onenote
Alpha globin gene cluster and its associated mutations
see onenote slides
Most of alpha-thalassaemia arise out of gene deletion
beta-thal can be either beta+ and beta0 depending on whether beta globin chains are present or absent
see onenote slides
Range of different sorts of mutation
mutation in promoter => beta+, G to A mutation at position 110 of first intron
Interesting form of thalassemia - intron mutation causing a disease
- 90% of globin produced is due to splicing at the new AG, rather than the normal AG acceptor site, abnormal beta-globin gene
- 10% has normal beta-globin gene
HbE
see onenote
- Beta-e gene = codon changes from G to A, produces new aa, negatively to positively charged aa
Beta-thal recessive/dominant
see onenote
Summary of alpha and beta thal
see onenote
Developmental control of gene expression in gamma, delta, beta globin gene cluster
- globin switching
- important for therapeutic approached based on influencing gene expression
Hb shifts
see onenote
Globin switching
something is missing - drive of beta globin gene expression requires more than just the promoter
- Switch is some interaction between the promoter and some regulatory sequence upstream
Evidence for additional regulatory sites
see onenote
From cell hybridisation studies
- globin gene turned on associated with revealing of several DNAse hypersensitive sites, which are known to identify regions of “active chromatin”
Switching - competition between promoters
see onenote
Competition between promoters
- Switching is due to competition between promoters
- Locus control region (LCR), distant to the gene and its promoter
- Even though it’s far from the gene, it can be brought together with the gene via DNA bending - why putting the gene and promoter in the mouse resulted in very low expression, it was missing the LCR
- LCR comprises hyper sensitive sites
Locus control region (LCR)
The locus control region (LCR) is a long-range cis-regulatory element that enhances expression of linked genes at distal chromatin sites. It functions in a copy number-dependent manner and is tissue-specific, as seen in the selective expression of β-globin genes in erythroid cells
Alpha globin genes also has regulatory elements that are distant from the genes
see onenote
Expression of globin genes in fetal and adult life
see onenote
Regulation of beta-like globin expression by KLF1 in adults
see onenote
KLF1 - additional regulatory protein
Activates beta-globin gene via protein, BCLIIA
Major TF involved in gamma to beta switch
see onenote
BCLIIA knock down
see onenote
- increases foetal Hb
- therapeutic potential to induce fetal Hb
Modifiers of globin gene expression
see onenote
KLF1 drives expression of fetal Hb in British HPFH
see onenote
Treatment of beta-thal
see onenote
- blood transfusions
- gene therapy
- Hydroxyurea
- demethylating drugs => reexpression of methylated gamma globin gene
- HDAC inhibitors and short chain fatty acid derivatives => inhibit histone deactylation
Other possibilities
see onenote
