Sickle Cell Disease: An Overview

by admin | June 18, 2020 11:39 am

19th of June is ‘World Sickle Cell Day’. Outside the medical fraternity, very few people are aware of this event, or even about this ailment. This article is aimed at educating readers on this less-known blood disorder. 

Sickle Cell Disease (SCD) is a group of blood disorders which are quite rare, but nevertheless a life-changing condition for those afflicted and their family members. 

Red Blood Corpuscles (RBCs) are an important component of human blood. They carry oxygen from the lungs to thousands of tissues all over the human body and help maintain overall health. Normally, these are disc-shaped and easily slide through even the narrowest of blood vessels. In some people however, some or all the RBCs deform and develop a crescent-moon or sickle-like shape. They become rigid or sticky and get stuck in narrow blood vessels, thereby reducing the blood flow[1] or oxygen transport within the body. This in turn causes a variety of conditions. 

Causes

There is very little consensus on what exactly causes the RBCs to deform in shape. It’s only known that SCD is an inherited or genetic disorder. Haemoglobin (Hgb) is a protein found in the human blood which is responsible for the transport of oxygen. Genetically speaking, its made up of 2 alpha and 2 beta chains. Mutations of these different genes cause a variety of SCD. 

Types of SCD

• HbSS or Sickle Cell Anaemia: This is the most common and most severe type of SCD. This is caused when the person inherits two sickle cell genes (HbS) one each from both parents.
• HbSC: The second most common type and a milder form of SCD. Here, the person has inherited one sickle cell gene (S) from one parent and a gene for abnormal haemoglobin (C) from another parent. 
• HbS beta thalassemia: Beta thalassemia is another blood disorder and a type of anaemia. When a person inherits a sickle cell gene (S) from one parent and a gene for beta thalassemia from another parent, it results in this condition. Since beta thalassemia is of 2 types – 0 and +, HbS beta thalassemia also has 2 variations where 0 presents severe symptoms of SCD and + milder ones. 
• HbSD, HbSE, and HbSO: Extremely rare types with mild symptoms. Here, the person has inherited the gene for SCD (S) from one parent and another gene for abnormal haemoglobin (D, E or O) from another parent. 
• HbAS or Sickle Cell Trait (SCT): Here, the person has inherited one gene for SCD (S) from one parent and perfectly normal blood (A) from another parent. The person can live a normal life without any symptoms or even awareness of the condition but he/she can pass on the SCT gene to the children. 

Risk Factors

Race and public health conditions are major risk factors. African Americans and Hispanics with a Caribbean ancestry are at high risk. Also countries where endemic malaria is common, show higher incidences of SCD. This includes Mediterranean, South East Asian countries (including India), and Saudi Arabia

Symptoms

In several states of the US, a newborn baby has to be mandatorily screened for SCD. However, no such law exists in India. So if you see your child displaying any of these symptoms, consult a doctor. 

• Anaemia: Sickle cells break and die quickly causing a shortage of RBCs in the blood, or anaemia. Anaemia results in constant fatigue and low-energy. 
• Severe pain: When the sickle-shaped RBCs get blocked in narrow blood vessels of the chest, abdomen and joints, it results in mild to severe pain episodes called Pain crises. The pain can occur in any part in the abdomen, chest or joints of the body, and can last from a few hours to a few weeks. Pain in the abdomen is also accompanied by a swelling that is painful to touch. 
• Hand-foot syndrome: When sickle cells get stuck in the narrow blood vessels of the limbs, blood flow is restricted causing swelling in the hands and legs. 
• Frequent infections: The blocked blood flow to the spleen can damage the spleen (called Splenic sequestration) and this increases the risk of various infections including life-threatening ones such as pneumonia. If the damage cannot be arrested through medications, the spleen shrinks in size and ceases to function. In such a case, the spleen may have to be removed (called splenectomy).
• Delayed growth or puberty: A shortage of healthy RBCs can delay growth in infants and children, and sexual maturity in teenagers. 
• Vision problems: Blockage in the tiny blood vessels of the eyes can damage the retina and cause vision problems. 
• Neurological[4] problems: Blockages in blood flow to the brain can result in seizures, stroke and even coma. One should watch out for symptoms of stroke or paralysis and seek emergency medical help. 
• Skin conditions: Blockages in the blood flow in legs can cause skin ulcers while in rest of the body; it can cause pale and yellow skin, pale nails and yellowish eyes.

Complications

• Heart and chest related: Blockage in the blood flow or oxygen supply to the heart result in cardiovascular conditions such as heart attack, heart failure[5] and irregular heart-beat (arrhythmia). Some people may suffer from what is called Sickle Chest Syndrome. This causes severe chest pain accompanied by cough, sputum, fever, shortness of breath and low blood oxygen. 
• Lung disease: Decreased blood flow to the lungs causes lung damage, resulting in high BP in the lungs (pulmonary hypertension) or scarring of the lungs (pulmonary fibrosis). Patients who have suffered a bout of sickle chest syndrome develop these conditions faster than those who didn’t. 
• Priapism: In this condition, the male patient suffers from long-lasting and painful erections which if left untreated can result in damage to penile blood vessels and hence impotence. 
• Gallstones: When RBCs breakdown due to SCD or any other cause, they create a by-product called bilirubin. When there is a high level of bilirubin the body, it causes gall-bladder[6] stones, or gallstones. 
• Organ damage: Restricted or reduced blood flow to major organs like liver, kidneys, spleen, heart and lungs results in various kinds of damage to these organs
• Pregnancy related: Women with SCD who are pregnant have a high risk of hypertensions (high BP), thrombosis (blood clots), miscarriage, premature birth and underweight babies. 

Diagnosis

A series of special blood tests are done to confirm or rule out SCD. 

• Blood count: This measures the haemoglobin level in the blood
• Electrophoresis: This detects and measures the different types of haemoglobin in the blood
• Blood film: This ascertains the shape of red blood cells
• Sickle solubility test: This straightaway looks for the presence of HbS

Treatment

SCD is a genetic disorder and cannot be fully cured as of now. However, there are various techniques to reduce the severity of SCD or to manage the pain from SCD. 

• Rehydration: Dehydration is known to be a trigger for RBCs deforming in shape. So, a SCD patient is rehydrated with IV fluids to force the RBCs to return to the normal shape.
• Managing infection: Managing various infections and keeping them under control help reduce the severity of a SCD pain crisis. 
• Blood transfusion[7]: Blood transfused from a healthy person increases the quantity of healthy RBCs in the blood and reduces the severity of SCD symptoms.
• Supplemental oxygen: Oxygen is given through a mask in order to improve oxygen levels in the blood. 
• Pain medication: Painkillers and over-the-counter prescription drugs help reduce the pain triggered by SCD. 
• Immunization: Boosting the immunity of the SCD patient helps reduce the risk of infection and hence the severity of SCD symptoms.
• Bone marrow transplants: Bone marrow from a matching donor (usually a sibling) is transplanted into the bones of SCD patient with severe symptoms.
  

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