Sickle Cell Anemia
Sickle cell disease or Sickle cell anaemia (SCA) is a type of anaemia where the red blood cells acquire a sickle shape because the protein haemoglobin in the cells is abnormal. It is a genetic blood disorder that occurs when a person inherits haemoglobin genes that are mutant from both parents. According to a World Health Report (2006), the mutant haemoglobin genes for sickle cell anaemia are widespread and about 5% population of people in the world carries these genes while 300, 000 infants are born with this haemoglobin disorder yearly. The report further affirms that the highest prevalence of haemoglobin disorders occur in people who descend from Saudi Arabia, sub-Saharan Africa, Mediterranean countries and India. Other terms like Sickle- cell disorder and Hemoglobin SS disease also describe sickle-cell anaemia. This paper will focus on the pathophysiology, genetic and clinical aspects of sickle cell anaemia and the disease prevalence in Saudi Arabia.
SCA is caused by defective haemoglobin in the human’s red blood cells (NIH, 2002; WHO, 2006). Haemoglobin is a protein component in the red blood cells responsible for oxygen transportation around the body. The haemoglobin is responsible for the red color of blood. In normal circumstances, the erythrocytes (red blood cells) are smooth round enucleated discs with a biconcave shape that allows for a higher packing of haemoglobin and increases the surface area to volume ratio for easier and quicker diffusion of oxygen from the blood to the body tissues. Moreover the shape allows them to squeeze through the blood vessels as they are transported around the body. The erythrocytes have a lifespan of 120 days in the circulatory system after which they are replaced with new ones from the bone marrow. On the other hand, in SCA, the abnormal haemoglobin causes the red blood cells to assume a crescent shape best referred to as the sickle shape. This shape allows for packaging of less haemoglobin and the erythrocytes have a difficulty passing through the blood vessels. Moreover, the shape causes the erythrocytes to have a low surface area to volume ratio therefore leading to low haemoglobin content and slower diffusion of oxygen. Erythrocytes in sickle cells die prematurely before the bone marrow is ready to synthesize newer cells therefore leading to reduced levels of red blood cells causing to anaemia. Abnormal haemoglobin results from a point mutation in the beta-globin chain. The condition is always present at birth but sometimes it takes four months before any symptoms are detected.
Genetic characterization of sickle cell
Chemical changes in the DNA can alter proteins as the SC disease exemplifies. SCA is the pioneer genetic disease in molecular characterization (Bustamante and Martinez, 2002). The haemoglobin consists of four globin units; 2 alpha globins and 2 beta globins which work together for oxygen circulation. The beta globin alleles A and S are significant in sickle cell inheritance where the A allele dominant homozygous form is “HBAA” while the S allele is mutant and therefore represents the homozygous mutant form “HbSS”. An individual with the dominant homozygous trait carries a copy of the dominant allele AA and therefore has normal haemoglobin and normal-shaped red blood cell. On the other hand, an individual with recessive homozygous trait carries a copy of the recessive alleles SS and therefore develops sickle cell shaped red blood cells. Such individuals develop the life-long sickle cell disease and experience the full blown symptoms of sickle cell anaemia. In other circumstances, an individual inherits allele A from one parent and allele S from another parent and posses the heterozygous condition “HBAS”. In this situation, both the A and S alleles are codominant because both kinds of haemoglobin are made in these individuals. Such individuals lead normal healthy lives and are referred to as carriers of the sickle cell trait. However, they can slightly suffer from sickle cell symptoms in low oxygen conditions for, instance in elevated heights. The only way to prove the presence of the mutant allele is through a blood test referred to haemoglobin electrophoresis that determines the kind of haemoglobin one has. Bustamante and Martinez (2002) assert that the inheritance of the haemoglobin alleles follow the Mendelian laws of genetics. The applied Mendelian law shows that half the offsprings have a chance to be HBs carriers where only one parent is a carrier. Conclusively, if both parents are carriers the offsprings have a 25 percent chance for HBAA, 50 percent chance for HBAS and 25 percent chance for HBSS. The heterozygous condition increases the frequency of sickle cell allele because the allele can be passed to the filial generation when the individual bears offspring with another heterozygous or homozygous recessive individual. The AS heterozygote also has another major advantage and this is the ability to resist the protozoan parasite that causes anaemia. With the invasion of the malaria parasites in the bloodstream, red blood cells with the mutant haemoglobin die therefore traps the parasites within the red blood cells and reduce the chance of infection. The AA is at a higher chance of dying from malaria while the SS dies prematurely of sickle cell anaemia although they resist malaria. The AA and SS alleles are removed from the gene pool whereas the frequency of AS alleles increases (Lehmann, Maranjian and Mourant, 1963). In molecular characterization, electrophoresis can be used to identify haemoglobin S and analysis can be done by ADN genotype methods.
Signs and symptoms of sickle-cell anaemia
As already seen an individual has to have homozygous recessive alleles to suffer from SCA which is hereditary disease of autosomic recessive nature. SCA sufferers experience both acute and chronic symptoms most of which cause their premature death (Lane, et.al, 2001; NIH, 2002). The sickle cell shape and staggering movement of the red blood cells cause interruption of blood circulation leading to organ harm a condition referred to as vaso-occlusive crisis leading to painful episodes or ischemia that occur at various intervals in their life time and can vary in severity. Some episodes are so severe that they require hospital stay. The painful symptoms can occur in the bones, abdomen and chest and organs like the lungs, gall and spleen are severely affected. In the long run, spleen infarction occur leading to a low immunity; a condition that predisposes the patient to microbial infections. Additionally, necroses of other important tissues and bones in the body occur and they get damaged because of the low oxygen supply (WHO, 2006). Episodes of breathlessness, dizziness, fatigue rapid and irregular heartbeat rate are also common due to the poor blood circulation and low oxygen levels in the body tissues. SCA persons usually have a delayed growth and reach puberty late as compared to the normal adolescents. Other common signs include dactylitis where hands and legs inflame and ulcerate especially at the adolescent and adult ages. They also experience jaundice where there is yellowing of skin and are faced with feelings of frequent thirst and frequent urination. Strokes can result at the interruption of blood supply to the brain tissues. Eye damage leads to poor eyesight and the skin becomes pale. Fever is also a common symptom in SCA patients. It should be noted that particular symptoms are faced with certain age groups while others are persistent throughout the life time of the individual. For instance, fevers and pneumococcal bacterial infections are mostly present in childhood while the pain crises affect all the ages.
There are several methods that can be used to diagnose SCA and these can be before birth, after birth or at the symptom onset for the purposes of detecting or confirming the disease. The tests include peripheral blood smear tests, antenatal screening and pre-implantation genetic diagnosis (PIGD). Blood tests can be used in SCA diagnosis and followed by haemoglobin electrophoresis to detect presence of the mutant haemoglobin. A full blood count can be done to reveal the levels of haemoglobin and determine the amount of defective haemoglobin where low amounts can suggest that the person is a carrier while high amounts suggest that the person has the disorder. Neonatal screening takes place at birth and during the baby’s development so that if sickle cell is detected, treatment and management options can be started early enough.
For disease detection, antenatal screening is done on the expectant mother to detect genetic disorders including SCA. The PGID method tests for SCA defects on the embryo and sperm of the couple in vitro. According to Lane, P., et.al. (2001), neonatal screening and other genetic pretests can provide medical interventions that will reduce chances of increasing the frequency of the defective allele.
Treatment and management of sickle cell anaemia
Currently there is no ultimate cure for SCA but ongoing scientific researches provide hope for the future. All the same there are several treatment options available to manage the symptoms of SCA after diagnosis and help SCA patients leave a normal life as much as possible (NIH, 2002). In penicillin prophylaxis, folic acid supplements and pneumococcal vaccines are administered to prevent severe bacterial infections, pneumonia episodes in children and increase the haemoglobin levels. Erythropoietin is a medication that improves the low blood count. Pain management is done by a range of analgesics and this includes the use of NSAIDs in adults. Psychological counseling is also important for both the patient and the family affected especially a parent; it is not easy living while knowing you could die any minute. Frequent blood transfusion is also necessary to prevent chances of stroke, pain crises and symptoms such as dizziness and breathlessness. However, the patients should also be put on treatment the can eliminate excess iron because an overload of this element causes toxicity and can lead to death. Hydroxyurea is another pharmacotherapeutic management for SCA and among the first approved drug for the condition. It has been shown to decrease the symptoms severity and lengthens the survival time by reducing the number of times that red blood cells change to sickle shape. A treatment that has proved to benefit especially the children is the bone marrow transplants that aids in faster manufacturing of the red blood cells. Depending with the severity of the symptoms and the nature of the drugs, antibiotics and other drugs can be administered orally or intravenously or a combination of the two methods. Research seeks gene therapy as a future treatment modality. Ways with which the haemoglobin switching can be modified are being studied and hopefully will provide a lasting solution to SCA.
Prevalence of sickle cell in Saudi Arabia
Haemoglobin disorders prevail in Saudi Arabia especially in the Eastern province of the region which is featured with the mild form of the disease (Al Arrayed and Haites, 1995). The lowest gene frequency is in the northern and central provinces but the common feature of all the provinces was a remarkable presence of HBAS in the areas with a high prevalence of the HBs allele. Despite the sickle cell trait inheritance being within family lines, the prevalence in the different regions of the world can be explained by other prevailing factors for instance malaria trends of a region that affects the haemoglobin alleles. According to Lehmann, Maranjian and Mourant (1963), the sickle cell haemoglobin distribution in the Saudi Arabia population is related to the malaria history of the region which alters the gene frequencies. There was an endemic of falciparum malaria in the region that only subsided in 1970.
Saudi Arabia faces the need to apply and reinforce a control program that will prevent a generation of homozygosity recessive for sickle cell anaemia. This can be done through the health care schemes and psychosocial education to prevent creation of a generation that can whither prematurely and therefore increasing economic and psychosocial constrains that can affect Saudi Arabia. Although there is a high prevalence of the sickle cell trait in Saudi Arabia, the recessive trait’s frequency is still low and therefore there is a low mortality rate from SCA. A definitive study was carried out by Ashour (2004), a haematologist, to determine the prevalence of SCA in primary school going children. The test was performed to 3,980 children of both the sexes and between age 6 and 12 years from different schools in Makkah city. They were subjected to the painless peripheral blood smear test and a haemoglobin electrophoresis carried out to determine the presence of the defective haemoglobin. Results showed that a total of sixty children had the sickle cell trait. Out of this 36 were boys and 24 were girls. The study is an important case that determines Saudi Arabia HBs allele frequency. Considering that Makkah is mainly a cosmopolitan city and there is an increased rate of consanguineous marriages, the chances of increasing the HBs frequency in all of the Saudi Arabia societies is very high. With the presence of a high HBAS frequency, neonatal and antenatal screening as well as genetic counseling should be fostered at the national level. This will reduce higher mortality and morbidity rates in the present and future Saudi Arabia, thereby protecting the socioeconomic structure. Additionally, the statistical data by Mulik et al show that about 73 per cent of children below the age of 3 years are likely to be diagnosed with the condition. At the same time, the severity of complications were twice the normal cases, with hand-foot syndrome being more pronounced, that is registered by about 58 percent of the 99 subjects.
Genetic disorders are on the rise and as much as no one can be blamed for the unfortunate gene match, allele frequency reduction can be achieved through genetic pretests and other healthy interventions. Sickle cell anemia is one such disorder that has ended many lives prematurely and increases the mortality and morbidity rates of a population. With a high mortality rate, a country is likely to be affected negatively economically. It is with enthusiasm that we expect scientists to determine ways of reversing mutations in the lethal genes and therefore reduce the default deaths caused by genetic disorders like SCA.