DISTRIBUTION OF HEMOGLOBIN GENOTYPES AMONGST RESIDENTS IN PORT HARCOURT

Transcription

1 DISTRIBUTION OF HEMOGLOBIN GENOTYPES AMONGST RESIDENTS IN PORT HARCOURT KEN-EZIHUO STELLA, DISEGHA, G.C., AND ADIMUO, PATRICIA O. ABSTRACT Key Words: Haemoglobin, haemoglobinopathy, electrophoresis, distribution, prevalence, genetic INTRODUCTION Hemoglobin is an intercellular protein in erythrocytes, consisting of four polypeptide globin chains, each of which is folded around a 'heme' molecule. It is responsible for the transportation of oxygen from lungs to the tissue and carbon dioxide from tissue to the lungs. The globin chains are encoded by their respective genes existing on the quantified trait locus (QTLs) on chromosome 11 and chromosome 16 and both known to have several alleles (Weatherall, 2011). Many of these alleles (genes) undergo point mutations in the DNA sequence that leads to amino acid substitutions, deletion or translocation in the globin moiety, resulting in the production of 210

2 Distribution Of Hemoglobin Genotypes Amongst Residents In Port Harcourt hemoglobin variants (Titus et al.,2006). Many of these mutants form of hemoglobin cause no disease, e.g. thalassemia. In beta thalassemia, the individual inherits one abnormal beta hemoglobin gene and normal beta gene from the other parent (heterozygous). So they rarely have symptoms of sickle cell disease. In exceptional circumstances a sickle crisis can arise on these individual e.g. high altitudes, involving a strenuous exercise or during prolonged anesthesia. It is reported that individuals with sickle cell are more prone to microbial infection, and that microbial "infection is a significant contributor to morbidity and mortality in sickle cell disease (SCD)" (Booth et al., 2010).This suggests a high susceptibility of sickle cell diseased individuals to infection by pathogenic bacteria (Booth et al., 2010). Meanwhile there are carriers who can pass the sickle cell gene to their offspring. These heterozygous individuals are called sickle cell trait or sicklemia (Cheesbrough, 2000). They have a 1-in-2 (50%) chance of passing the sickle cell trait to any of their offspring. If both parents have sickle cell trait gene, any of their offspring would have a 1- in-4 (25%) chance of having a sickle cell anemia (Hb SS). These abnormal haemoglobin genotypes occur when an affected individual inherits mutated globin gene such as hemoglobin S, C, D, E, from both parents. Abnormal hemoglobin genotype is inherited in an autosomal co-dominant fashion and occurs by different combinations (Weatheral, 2011). However, these mutant forms of hemoglobin cause a group of hereditary disease known as haemoglobinopathy. The commonest known haemoglobinopathy is sickle cell disease, which was the first human disease whose mechanism was understood at molecular level. The World Health Organization (WHO) figures estimate that 6% of the world population is a carrier for Hemoglobin disorders (Patel et al., 2009). The highest prevalence of sickle cell disorder is found among people of African or Caribbean descent and may occur among those from the Eastern Mediterrenean, Middle East, India and Pakistan (Erhabor et al., 2010). When normal red blood cells are viewed under the microscope, they are round and biconcave in structure while in sickle cell disease they appear sickled in shape because during deoxygenation, the red blood (RBC) shape changes from the biconcave shape to the sickle shape due to the abnormal hemoglobin. When reoxygenated the red cell changes back to biconcave shape. However, the frequent sickling and unsickling cause hemolysis which causes anemia (Alagbe, 2013). These group of individuals are usually anaemic; and always experience shortage of blood because their RBC break easily and their RBCs wear out every days to opposed days of individual with normal RBCs (Gladwin and Sachdev, 2012). The most common 211

3 Nigerian Journal Of Oil And Gas Technology - Vol 3 No. 1 encountered abnormal hemoglobin genotypes among Nigerians include AS, AC, SC and SS. It has been reported that abnormal hemoglobin genotypes have been associated with a wide range of moderate to severe hemolytic anemia leading to a high degree of morbidity and mortality among affected individuals as well as susceptibility to renal medullary carcinoma and hyposthenuria (Akigbe et al., 2009; Patel et al., 2008). Genotype is a complete genetic constitution of an individual at a particular location (locus) in the genome. At many locations (loci) throughout the genome, the chromosomal DNA sequence differs subtly between individuals. Each of various DNA sequence at one locus is called an allele; for instance, if there are three sequence variants present, then there are three alleles. Off springs inherit one homologous chromosome from each parent. Thus, a genotype is made up of two alleles; one inherited from the father (paternal chromosome) and the other inherited from the mother (maternal chromosome) (Millodot, 2009).Genotypes found in RBCs are termed "AA", "AS", "AC" or "SS", "CC" and "SC", the last 3 types are seen in sickle cell disease. Sickle cell disease (SCD) has been known to be an inherited blood disorder that affects the red blood cells, and has also been primarily considered a disease of children with few patients surviving to adulthood. Between , the median survival of patients with SCD was < 20 years of age (Kumar et al., 2009). That sudden death occurred in about 41% of the patients, whereas 29% death occurred within 24 hours after the onset of painful crises (Prabhakar et al., 2010). According to one study performed in Jamaica, in 2001 the estimated mean survival for people with sickle-cell was 53 years old for men and 58 years old for women with homozygous SCD (Kumar et al., 2009). The specific life expectancy in most of the developing world is unknown (Costa et al., 2016). These groups of individual have their adult hemoglobin S (HbS) in their red blood cells to oppose the normal hemoglobin A (HbA) and the difference between HbA and HbS is only one protein out of about 300 that are common to both. These proteins lie along an amino acid chain called beta-globin, and cause the red cell to become sickle-shaped (Crescent shaped) thereby making them difficult to pass through the small blood vessels, and then cause blockage of the capillaries (Odieve et al., 2011), These blockage reduces the blood flow to some tissues, while the tissue that do not get normal blood flow eventually become damaged. Red blood cells are produced regularly to replace old ones, but are destroyed faster in sickle cells that the body cannot cope with. The RBC count drops, which result in anemia, jaundice, pain episodes, swelling of the hands and feet. Other negative effects of sickle cell include damage of organs 212

4 Distribution Of Hemoglobin Genotypes Amongst Residents In Port Harcourt like liver, spleen and rarely; lymph glands (Prabhakar et al., 2010). Normal red blood cell contains hemoglobin A, and the red blood cells are soft and round, and can squeeze through tiny blood vessels. Their life span is days before their components are recycled by microphages and removed from the circulation by Endoplasmic Reticulum(ER) (Pierige et al., 2008). In abnormal hemoglobin S, C, D& E, the red blood cells only live for a short period of about 16 days and thereafter become stiff, distorted in shape, and become difficult to pass through a tiny blood vessels, causing blockage, reducing the blood flow, preventing tissues from getting nourishment and causing tissue damage which leads to anemia, jaundice and the formation of gall stones. Acute chest syndrome, pains on (legs, arms, chest and abdomen, and damage to most organs e.g. spleen, liver and kidneys, may occur (Lane and Githens, 2005). It is anticipated that the global economic burden of the hemoglobin abnormalities on public health will increase over the coming decades (Weatherall et al., 2010). The frequencies of these inherited characters have been extensively reported in various populations and ethnic groups in Nigeria (Erhabor et al., 2010).However, the dearth of published data on the distribution pattern and frequency of these hemoglobin variants from South-South region of Nigeria representing the three ethnic groups in Nigeria. Therefore, this study is aimed at providing information on the frequency distribution of hemoglobin variants among the three ethnic groups in Nigeria residing in Port Harcourt, Rivers State. The results that will be obtained would create more awareness especially on the benefits of knowing ones genotype prior to marriage in order to reduce the number of people with sickle cell disease. It will also educate the masses on the current diagnosis of sickle cell disease. Several hundred abnormal hemoglobin genotypes have been discovered, only a few are common and cause major public health problems in many parts of the world (Weatherall, 2011). According to the World Health Organization, Nigeria ranks first as the sickle cell endemic country in the world with an annual infant death of 100,000 representing 8% of infant mortality in the country. The World Health Organization also reported that averages of 150,000 infants are born with sickle cell disease in Nigeria (WHO 2006). The result of this study will also form the basis for providing genetic counseling services to students on matters that concern crucial decisions on marriage and blood transfusion which will help to reduce hemoglobinopathies and hemolytic diseases. This in turn will be reflected by the drop in morbidity and mortality from such conditions. This research is justified by the scarcity of published information distribution of hemoglobin 213

5 Nigerian Journal Of Oil And Gas Technology - Vol 3 No. 1 electrophoretic patterns of the three major ethnic groups in Nigeria residing in Port Harcourt, Rivers State. This study was therefore carried out to determine frequency and hemoglobin electrophoretic distribution patterns of the three major ethnic groups in Nigeria residing in Port Harcourt. MATERIALS AND METHOD STUDY AREA AND POPULIATION This research work was carried out in Port Harcourt capital of Rivers State in the, South-South part of Nigeria. Port Harcourt features a tropical wet climate with lengthy and heavy rainy seasons and very short dry seasons. Only the months of December and January truly qualifies as dry season months in the city. The harmattan, which climatically influences many cities in West Africa, is less pronounced in Port Harcourt. Port Harcourt's heaviest precipitation occurs during September with an average of 367 mm of rain. December on average is the driest month of the year, with an average rainfall of 20 mm. Temperatures throughout the year in the city are relatively constant, showing little variation throughout the course of the year. Average temperatures are typically between 25 C-28 C in the city.(ref) A total of 156 adult males and females were recruited. The participants gave their verbal, informed consent and were offered pre- and post-test counseling. The recruited subjects were taken from three ethnic groups in Nigeria, namely Igbo, Hausa and Yoruba, all resident in Port Harcourt, the capital of River State. SAMPLE COLLECTION 2.0mls blood samples were collected from each subject by venipuncture into tri-potassium ethylene diamine tetracetic acid ( EDTA) anticoagulated tubes and properly mixed to avoid K3 clotting and labeled. METHOD: Haemoglobin electrophoresis. PRINCIPLE: This test is based on the ability of different haemoglobins to migrate within an electric field. 214

6 Distribution Of Hemoglobin Genotypes Amongst Residents In Port Harcourt Haemoglobin variants separate at different rates due to differences in their surface electrical charge as determined by their amino acid structure. PROCEDURE: Small quantity of haemolysate of venous blood from each of the subjects was placed on a cellulose acetate membrane It was carefully introduced into Shandon Electrophoretic tank containing tris-edtaborate buffer at ph 8.6. Electrophoretic separation was then allowed to operate for minutes at an electro motive force (emf) of 160V. The results were read immediately. Haemolysate from blood samples of known haemoglobin (AA, AS, AC) were run as controls. RESULTS AND DISCUSSION In this study, haemoglobin electrophoretic distribution pattern was determined among three major ethnic groups in Nigeria (Igbo, Hausa and Yoruba) resident in Port Harcourt, River state. Table1. Shows the Mean and standard deviation of different haemoglobin (Hb) electrophoretic pattern among the study population. Table2. Shows Frequency and distribution pattern of different haemoglobin (Hb) electrophoretic pattern among the study population The percentage distribution of different forms of haemoglobin (Hb) among the subjects was; Hb AA 111 (71.15%), HbAS 44(28.21%) and HbAC 1(0.64%). Among the male subjects, 93(75.61%) were HbAA, 30(24.39%) were HbAS and 0% males subject had HbAC. Among the 33 female subjects, 18 (54.55%) were HbAA, 14(42.42%) were HbAS; 1(3.03%) was HbAC. Table3. shows the frequency and distribution of different haemoglobin (Hb) electrophoretic pattern among the study population based on ethnicity, Igbo were (HbAA 36(69.23%) and HbAS 16(30.77%)), and Hausa were (HbAA 39 (76.47%) and HbAS 12 (23.53%) and Yoruba were ((HbAA 36(67.94%), HbAS 16(30.19%) and HbAC 1 (1.89%)). The data of subjects were analyzed using SPSS (Statistical Program for Social Sciences) version

7 Nigerian Journal Of Oil And Gas Technology - Vol 3 No. 1 Table1. Mean + standard deviation of different haemoglobin (Hb) electrophoretic pattern among the study population. S/N Hb Mean ±std 1 AA 37.00± AS 14.67± AC 0.33± SS - Table2. Frequency and distribution pattern of different haemoglobin (Hb) electrophoretic pattern among the study population Sn Hb IGBO HAUSA YORUBA %Hb 1 AA (71.15%) 2 AS (28.21%) 3 AC (0.64%) 4 SS % Table3. Frequency and distribution of different haemoglobin (Hb) electrophoretic pattern among the study population based on ethnicity S/N Hb IGBO HAUSA YORUBA 1 AA 36 (69.23%) 39 (76.47%) 36 (67.94%) 2 AS 16 (30.77%) 12 (23.53%) 16 (30.19%) 3 AC (1.89%) 4 SS - - 0% TOTAL Table 4. Frequency and gender distribution of different haemoglobin (Hb) electrophoretic pattern among the study population S/N Hb MALE FEMALE 1 AA 93 (75.61%) 18 (54.55%) 2 AS 30 (24.39%) 14 (42.42%) 3 AC - 1 (3.03%) 4 SS - 0% TOTAL

8 Distribution Of Hemoglobin Genotypes Amongst Residents In Port Harcourt In this study, the frequency of HbAA was (71.15%). This finding is consistent with previous reports in which a prevalence of 80.32% (Jeremiah, 2006) and 69.1% was obtained among subjects in the Niger Delta of Nigeria (Akhigbe et al., 2009). The observed frequency of HbAA is also within the normal range of 55 75% earlier reported for Blacks (Bakare et al., 2004). The prevalence of HbSS among the black population in the United States, was reported to be 9% and 30 40% generally for Africans (Bakare et al., 2004). The frequency of sickle cell trait (AS) is consistent with prevalence reported for Africa (Nwafor and Banigo, 2001). Sickle haemoglobin (HbS) is the most common and clinically significant haemoglobin structural variant. This study has shown that prevalence of HbSS was 0% among subjects studied. This finding is consistent with other published reports in Nigeria; 3.0% in the South-West region of Nigeria 2% among under- graduate students in Bayelsa State and 3% in Rivers State (Egesie et al., 2008) both in the South-South of Nigeria. This study however, supports the research done on 620 University students in Port Harcourt Nigeria (Jeremiah, 2006).Which reported a 0% prevalence of HbSS. The zero frequency observed in these studies, possibly imply that the sickling gene pool is gradually reducing in some African populations due to increased awareness and pre-marital counselling. The low prevalence of HbSS observed in these studies could be attributed to increased awareness of the disease, improved socio-economic conditions, improved pre-marital counselling, environmental and genetic factor which have an overall effect on the sickling gene pool. The zero prevalence may also be attributed to an active program of prenatal diagnosis among pregnant women in Nigeria. By comparison, the prevalence of HbSS among the black population in the United States is reported to be 9% and 30% 40% generally for Africans (Gulbis et al., 2009). Evidenced -based data from Belgium, a country with universal neonatal screening programme has shown that neonatal screening is an excellent health education tool (Tshilolo et al., 2008). The Nigerian government can benefit by implementing a similar program in a bid to improving the healthcare services offered to patients with haemoglobin disorders (Moormann et al., 2003).There is also a need for sickle cell disease clinical care programs which should include: infection prophylaxis with penicillin and malarial prophylaxis; family training to identify early, severe, or persistent symptoms and increased awareness of the gravity of malarial crises; the evaluation of the patient's nutritional status and fluid intake; and education about the importance of regular medical visits. The frequency of HbAS observed in this present study was (28.21%). This finding is in 217

9 Nigerian Journal Of Oil And Gas Technology - Vol 3 No. 1 agreement with prevalence of 20 30% quoted for Nigeria and 20 40% for Africa in general (Jeremiah, 2006). This study findings are much higher than a prevalence of 1.15% observed in Bengal, India (Roberts and Williams, 2003). Considerable evidence has been provided to show that these traits do confer protection from malaria (Williams, 2012). Evidence exists on the protective role against clinical Plasmodium falciparum malaria (Verra et al., 2007). This study also observed a prevalence of HbAC 0.33% for subjects studied. This study is also consistent with a 1% prevalence of HbC reported in a previous study in Ecuador, a tropical Latin-American country with an important presence of Afro-descendants (Modiano et al., 2001). Haemoglobin C (HbC) is one of the commonest structural haemoglobin variants in human populations. Although HbC causes mild clinical complications, its diagnosis and genetic counselling are important to prevent inheritance with other haemoglobinopathies (Verra et al., 2007). Haemoglobin C (HbC) is a structural variant of normal haemoglobin (HbA) caused by an amino acid substitution at position 6 of the â-globin chain (â6glu-lys) (Dominguez et al., 2013). Homozygosity (CC) causes clinically mild haemolytic anaemia, due to the reduced solubility of the red blood cells which can lead to crystal formation (Njamnshi et al., 2006). HbC is mainly of clinical significance when inherited in combination with HbS (sickle-haemoglobin C disease), causing chronic haemolytic anaemia and intermittent sickle cell crises, slightly less severe or frequent than in homozygous HbS patients (SS), and when co-inherited with â-thalassaemia (haemoglobin C-â thalassaemia), causing moderate haemolytic anaemia with splenomegaly. Despite being the most prevalent genetic disease in Africa and associated with serious health and socioeconomic impacts, Sickle cell disease is largely neglected (Creary et al., 2007). CONCLUSION AND RECOMMENDATION Data from the present study showed that the frequency and distribution of haemoglobin electrophoretic pattern among major three ethnic group (Igbo, Hausa and Yoruba) residing in Port Harcourt, Rivers State is more of HbAA ( 71.15%) and with no trace of HbSS, an indication that sickling gene pool is gradually reducing in Nigeria and some African populations due to increased awareness and pre-marital counselling. However, comprehensive research is required to ascertain the prevalence and distribution of haemoglobin electrophoretic pattern among any population in Nigeria which will be useful in healthcare planning, appropriate allocation of resources, and justification of the need for appropriate pre-marital and prenatal diagnosis and genetic counselling policy as an avoidance strategy to reduce the incidence of haemoglobinopathies in Nigeria. 218

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