Sickle cell anaemia: Difference between revisions
mNo edit summary |
No edit summary |
||
| Line 1: | Line 1: | ||
Sickle cell anaemia is an autosomal [[Recessive disorder|recessive disorder]], which leads to deformation of the shape of the [[Red blood cells|red blood cells]], which then prevent the [[Cell|cells]] being able to travel through small blood vessels. This then deprives organs and tissues of [[Oxygen|oxygen]]. Sufferers experience a lot of pain and | Sickle cell anaemia is an autosomal [[Recessive disorder|recessive disorder]], which leads to deformation of the shape of the [[Red blood cells|red blood cells]], which then prevent the [[Cell|cells]] being able to travel through small blood vessels. This then deprives organs and tissues of [[Oxygen|oxygen]]. Sufferers experience a lot of pain, referred to as a crisis and the condition can lead to other serious medical problems. | ||
=== Genetics === | === Genetics === | ||
Sickle cell is an genetic disorder caused by a mutation in the [[Amino acids|amino acid]] sequence coding for the [[Haemoglobin gene|haemoglobin gene]] <ref>Biochemistry 6th edition Jeremy M. Berg, John L Tymoczko, Lubert Stryer pg 195</ref>. This mutation is caused by a [[Hydrophobic|hydrophobic]] [[Valine|valine]] (V) replacing [[Glutamic acid|glutamic acid]] otherwise known as glutamate (E)in position 6 of the [[Beta haemoglobin chain|beta haemoglobin chain]]. Hence sickle cell is denoted as E6V .The new [[Valine|valine]] lies on the surface of the T-state [[Molecule|molecule]], this new [[Hydrophobic|hydrophobic]] patch interacts with another [[Hydrophobic|hydrophobic]] patch on the [[Haemoglobin|haemoglobin]], which initiates aggregation. The aggregates form long fibres which stiffen the normally flexible [[Red blood cells|red blood cells]] . This leads to distortion of the [[Red blood cells|red blood cells]] and leads to [[Capillary|capillary]] occlusion, preventing the delivery of [[Oxygen|oxygen]] to body tissues. The mutation is known as HbS, the normal [[Haemoglobin|haemoglobin]] is referred to as HbA.<br> | Sickle cell is an genetic disorder caused by a mutation in the [[Amino acids|amino acid]] sequence coding for the [[Haemoglobin gene|haemoglobin gene]] <ref>Biochemistry 6th edition Jeremy M. Berg, John L Tymoczko, Lubert Stryer pg 195</ref>. This mutation is caused by a [[Hydrophobic|hydrophobic]] [[Valine|valine]] (V) replacing [[Glutamic acid|glutamic acid]] otherwise known as glutamate (E)in position 6 of the [[Beta haemoglobin chain|beta haemoglobin chain]]. Hence sickle cell is denoted as E6V .The new [[Valine|valine]] lies on the surface of the T-state [[Molecule|molecule]], this new [[Hydrophobic|hydrophobic]] patch interacts with Leucine in position 8 another [[Hydrophobic|hydrophobic]] patch on the [[Haemoglobin|haemoglobin]], which initiates aggregation. The aggregates form long fibres which stiffen the normally flexible [[Red blood cells|red blood cells]] . This leads to distortion of the [[Red blood cells|red blood cells]] and leads to [[Capillary|capillary]] occlusion, preventing the delivery of [[Oxygen|oxygen]] to body tissues. The mutation is known as HbS, the normal [[Haemoglobin|haemoglobin]] is referred to as HbA.<br> | ||
=== Inheritance === | === Inheritance === | ||
Sickle cell is a [[Recessive autosomal disorder|recessive autosomal disorder]], therefore two defected [[Gene|genes]] are needed (SS) for sickle cell anaemia. If one parents were to be a carrier of the [[Gene|gene]], (SA), each child would have a 25% chance of inheriting two sickle cell [[Gene|genes]], 25% chance of inheriting two normal [[Gene|genes]], and 50% chance of becoming a carrier like the parents. <br> | Sickle cell is a [[Recessive autosomal disorder|recessive autosomal disorder]], therefore two defected [[Gene|genes]] are needed (SS) for sickle cell anaemia. If one parents were to be a carrier of the [[Gene|gene]], (SA), each child would have a 25% chance of inheriting two sickle cell [[Gene|genes]], 25% chance of inheriting two normal [[Gene|genes]], and 50% chance of becoming a carrier like the parents. <br> | ||
=== '''Sickle-Cell Trait''' === | === '''Sickle-Cell Trait''' === | ||
When people carry both the [[Haemoglobin|Hb]]B [[Gene|gene]] and the mutated [[Haemoglobin|Hb]]S [[Gene|gene]] they are said to have sickle-cell trait. They are relatively unaffected by the symptoms associated with sickle cell anaemia, however they can pass the HbS [[Mutation|mutation]] onto their offspring. The interesting point here is that people with sickle-cell trait are resisitant to malaria. The | When people carry both the [[Haemoglobin|Hb]]B [[Gene|gene]] and the mutated [[Haemoglobin|Hb]]S [[Gene|gene]] they are said to have sickle-cell trait. They are relatively unaffected by the symptoms associated with sickle cell anaemia, however they can pass the HbS [[Mutation|mutation]] onto their offspring. The interesting point here is that people with sickle-cell trait are resisitant to malaria. The reason for this higher resistance is becasue the plasmodium parasite that casies the symptoms of Malaria grows poorly in sickled cells. This means that if a person has a proportion of sickled cells in his blood, there is a probability that some of the plamosdium parasite will affect the sickled cells, meaning that the attack on normal cells is lower than in an individual without the trait. | ||
The lethal nature of malaria and its prevalance in West Africa goes towards explaining the prevalance of the [[Haemoglobin|Hb]]S [[Alleles|allele]] in West African populations (1 in 100 West Africans being Sickle Cell Anaemia sufferers), due to the presence of the [[Haemoglobin|Hb]]S [[Alleles|allele]] favouring the survival of its carriers <ref>Biochemistry 6th edition Jeremy M. Berg, John L Tymoczko, Lubert Stryer pg 195-196</ref>. References <br> | |||
<references /> | <references /> | ||
Revision as of 19:33, 29 November 2011
Sickle cell anaemia is an autosomal recessive disorder, which leads to deformation of the shape of the red blood cells, which then prevent the cells being able to travel through small blood vessels. This then deprives organs and tissues of oxygen. Sufferers experience a lot of pain, referred to as a crisis and the condition can lead to other serious medical problems.
Genetics
Sickle cell is an genetic disorder caused by a mutation in the amino acid sequence coding for the haemoglobin gene [1]. This mutation is caused by a hydrophobic valine (V) replacing glutamic acid otherwise known as glutamate (E)in position 6 of the beta haemoglobin chain. Hence sickle cell is denoted as E6V .The new valine lies on the surface of the T-state molecule, this new hydrophobic patch interacts with Leucine in position 8 another hydrophobic patch on the haemoglobin, which initiates aggregation. The aggregates form long fibres which stiffen the normally flexible red blood cells . This leads to distortion of the red blood cells and leads to capillary occlusion, preventing the delivery of oxygen to body tissues. The mutation is known as HbS, the normal haemoglobin is referred to as HbA.
Inheritance
Sickle cell is a recessive autosomal disorder, therefore two defected genes are needed (SS) for sickle cell anaemia. If one parents were to be a carrier of the gene, (SA), each child would have a 25% chance of inheriting two sickle cell genes, 25% chance of inheriting two normal genes, and 50% chance of becoming a carrier like the parents.
Sickle-Cell Trait
When people carry both the HbB gene and the mutated HbS gene they are said to have sickle-cell trait. They are relatively unaffected by the symptoms associated with sickle cell anaemia, however they can pass the HbS mutation onto their offspring. The interesting point here is that people with sickle-cell trait are resisitant to malaria. The reason for this higher resistance is becasue the plasmodium parasite that casies the symptoms of Malaria grows poorly in sickled cells. This means that if a person has a proportion of sickled cells in his blood, there is a probability that some of the plamosdium parasite will affect the sickled cells, meaning that the attack on normal cells is lower than in an individual without the trait.
The lethal nature of malaria and its prevalance in West Africa goes towards explaining the prevalance of the HbS allele in West African populations (1 in 100 West Africans being Sickle Cell Anaemia sufferers), due to the presence of the HbS allele favouring the survival of its carriers [2]. References