L15 and L16 Sickle Cell Anaemia

Question 1

Haemoglobinopathies

Answer 1

Diseases of Hb

Question 2

Human Globin Gene Clusters

Answer 2

See onenote

• alpha globin clusters
• beta globin clusters

Question 3

Formation of Hb fusion genes

Answer 3

see onenote slides

• occur via unequal crossovers
• Give rise to certain types of Hb which are disease Hb

Question 4

Sickle Cell Anaemia

Answer 4

HbS

• balanced polymorphism
• malaria, selective pressure of sickle cell anaemia

Question 5

Sickle beta globin mutation

Answer 5

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

Question 6

From genotype to phenotype is sickle cell anaemia

Answer 6

see onenote slides and diagram

Question 7

Quantitative abnormalities of Hb

Answer 7

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

Question 8

Thalassaemia features

Answer 8

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

Question 9

Linkage disequilibrium

Answer 9

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

Question 10

Schematic of human beta globin gene

Answer 10

see onenote

illustrates possibilities for altered expression

Question 11

Phenotype of RBC - normal, alpha-thal, beta-thal

Answer 11

see onenote

Question 12

Alpha globin gene cluster and its associated mutations

Answer 12

see onenote slides

Most of alpha-thalassaemia arise out of gene deletion

Question 13

beta-thal can be either beta+ and beta0 depending on whether beta globin chains are present or absent

Answer 13

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

Question 14

HbE

Answer 14

see onenote

• Beta-e gene = codon changes from G to A, produces new aa, negatively to positively charged aa

Question 15

Beta-thal recessive/dominant

Answer 15

see onenote

Question 16

Summary of alpha and beta thal

Answer 16

see onenote

Question 17

Developmental control of gene expression in gamma, delta, beta globin gene cluster

Answer 17

• globin switching

- important for therapeutic approached based on influencing gene expression

Question 18

Hb shifts

Answer 18

see onenote

Question 19

Globin switching

Answer 19

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

Question 20

Evidence for additional regulatory sites

Answer 20

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”

Question 21

Switching - competition between promoters

Answer 21

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

Question 22

Locus control region (LCR)

Answer 22

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

Question 23

Alpha globin genes also has regulatory elements that are distant from the genes

Answer 23

see onenote

Question 24

Expression of globin genes in fetal and adult life

Answer 24

see onenote

Question 25

Regulation of beta-like globin expression by KLF1 in adults

Answer 25

see onenote

KLF1 - additional regulatory protein
Activates beta-globin gene via protein, BCLIIA

Question 26

Major TF involved in gamma to beta switch

Answer 26

see onenote

Question 27

BCLIIA knock down

Answer 27

see onenote

• increases foetal Hb
• therapeutic potential to induce fetal Hb

Question 28

Modifiers of globin gene expression

Answer 28

see onenote

Question 29

KLF1 drives expression of fetal Hb in British HPFH

Answer 29

see onenote

Question 30

Treatment of beta-thal

Answer 30

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

Question 31

Other possibilities

Answer 31

see onenote