Sickle cell aneamia

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Sickle cell aneamia is an inherited condition passed down through the family where the blood cells change shape once deoxygenated to form a crescent shape. Hence the name Sickle Cell Aneamia. The sickle cells are unable to efficiently deliver oxygen around the body, which can present the host with several different medical complications. Another problem that arises with the condition is that the cell can become stuck in smaller vessels restricting blood flow further.

Contents

Causation

Sickle Cell Aneamia is a inherited homologous recessive condition. This means both your parents must carry one copy of the recessive allele and you must inherit both recessive alleles to contract the disease. This is due to the recessive nature of the disease where by if only one of the recessive allele is present the dominant allele will mask the condition and the offspring would only be a carrier of the gene. Sickle Cell Aneamia is condition that shows how important the specificity of the DNA sequence must be. Sickle cell aneamia is caused by a substitution mutation of Adenine to a Thymine. This causes the translated amino acid to change from a Glutamic Acid to Valine in position 6 (abbreviated E6V)[1]. The result of this base mutation is that the Valine is able to bind to another hydrophobic amino acid. This cause long polymers, which can cause blockages within the vessels.[2]

Symptoms

Patient may exhibit symptoms from as young as 4 months old. These can vary in severity some symptoms have been listed below.
▪ Fatigue
▪ Paleness
▪ Rapid heart rate
▪ Shortness of breath
▪ Yellowing of the eyes and skin (jaundice)
▪ Younger children with sickle cell anemia have attacks of abdominal pain.

The following symptoms may occur because the abnormal cells may block small blood vessels:
▪ Painful and prolonged erection (priapism)
▪ Poor eyesight or blindness
▪ Problems thinking or confusion caused by small strokes
▪ Ulcers on the lower legs (in adolescents and adults)

Over time, the spleen no longer works. As a result, people with sickle cell anemia may have symptoms of infections such as:
▪ Bone infection (osteomyelitis)
▪ Gallbladder infection (cholecystitis)
▪ Lung infection (pneumonia)
▪ Urinary tract infection
▪ Other symptoms include:
▪ Delayed growth and puberty
▪ Painful joints caused by arthritis[3]

Example Of Positive Mutation

Sickle Cell Aneamia has had some positive effects on Africa populations. The malaria parasite is unable to develop properly within the mutated red blood cell whether the host is homozygous for the disease or heterozygous. This is why malaria is rarely seen within carrier or infected populations of people.[4]

References

  1. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman
  2. Hartl, D et al (2012). Genetics; Analysis Of Genes And Genomes. 5th ed. USA: Jones & Bartlett Learning. p524.
  3. Yi-Bin Chen. (2012). Sickle cell anemia . Available: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001554/. Last accessed 23rd Nov 2012.
  4. Alberts, B et al (2008). Molecular Biology Of The Cell. 5th ed. New York: Garland Science. p1495.

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