SICKLE CELL ANAEMIA

 
Sickle cell anemia is one of the common causes of anemia. Anemia is defined as a state of reduced red blood cells or the hemoglobin which they contain. Sickle cell anemia is a genetic disorder passed on from parents to offsprings in an autosomal recessive pattern. This means that its expression does not depend on the gender of the offspring (autosomal) and the offspring needs to inherit one abnormal gene each from both parents in order to have the disorder (recessive). There are however other conditions which may arise if an offspring inherits the abnormal gene from only one parent. These, along with the SCA are collectively grouped as Sickle Cell Disease, SCD. These offsprings with only one defective gene are referred to as carriers of the Sickle cell trait because they can also pass it on to their children and can have children with sickle cell anemia if the other parent is also a carrier of the trait. Carriers usually appear normal, without any form of anemia but some may have minor anemia and other symptoms experienced by SCA patients. 

The genetic abnormality in Sickle cell disease is a mutation in a single nucleotide of the gene coding for β globin, located on chromosome 11.  Hemoglobin, a protein found in red blood cells, is normally made up of 2α and 2βglobin chains. Red blood cells are able to carry oxygen around the body mainly because of the presence of hemoglobin in them. Most of the oxygen in blood is chemically bound to hemoglobin and release when needed.  Normal hemoglobin is called hemoglobin A (Hb A).  The gene mutation in SCD gives rise to the production of structurally defective β globins which in turn cause the formation of abnormal hemoglobin molecules called hemoglobin S (Hb S). Under conditions of low oxygen concentration, the deoxygenated Hb S molecules aggregate, forming fibrous polymers. This does not occur with normal hemoglobin. The fibrous precipitates formed cause the red blood cell to change its shape from the normal disc shape to a sickle shape. Sickle shaped cells are not elastic and are therefore easily destroyed as they pass through small blood vessels and spleen.  This gives rise to the chronic anemia and jaundice (yellow sclera of the eyes) seen in SCA. Sickle cells have a lifespan of about 10-20 days compared to 120 days for normal cells. This rate of destruction is too fast to be compensated by production of new cells. Also, many sickle cells can aggregate and block small vessels giving rise to the various forms of vaso-occlusive crisis and other complications. The symptoms however do not
 occur until after the age of 6 months when the level of the fetal hemoglobin, Hb F, decreases and production of Hb S increases.

From Sore Throat to Heart Disease

(RHEUMATIC HEART DISEASE)

Rheumatic heart disease is a permanent heart valve damage resulting from one or repeated episodes of rheumatic fever. Acute rheumatic fever is an abnormal immune response by the body to an infection (usually a throat infection) caused by bacteria called group A streptococci. Normally, one of the ways in which the body fights infections is by producing antibodies which attack the infecting organisms. In acute rheumatic fever, the antibodies produced are thought to also attack the host’s tissues (brain, skin, subcutaneous tissues, joints and heart) causing an inflammatory damage several weeks after the throat infection. This autoimmune response is seen in about 0.3-30% of patients with untreated or poorly treated group A streptococcal throat infection. Rheumatic heart disease is the most serious complication of rheumatic fever. Almost half of patients with acute rheumatic fever will have the heart involvement. 
                                             

The most commonly affected valve is the mitral valve followed by the aortic valve. Other valves (tricuspid and pulmonary are less frequently affected).The damage causes the flaps of the valve to thicken causing narrowing of the valve opening (stenosis). Repeated episodes of rheumatic fever further damage the valves and eventually lead to heart failure as less blood is pumped out of the heart but rather backs up in the left atrium, pulmonary veins and lungs. At this stage, except the valves are replaced with prosthesis, the patient will die of consequences of the heart failure. During an acute episode of rheumatic fever, the valvular damage may be minor and still be reversible. Symptoms of rheumatic heart disease include: shortness of breath, fatigue, irregular heartbeats, chest pain and fainting.