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A History of Sickle Cell Disease

Contents

  1. 1 The Evolution of Sickle Cell
  2. 2 1910 – First Description of Sickle-Shaped Blood Cells by Dr James Herrick
  3. 3 1917 – Genetic basis for SCD Dr. V. Emmel
    1. 3.1 Haemoglobin
    2. 3.2 Inheritance of Sickle Cell Disease
  4. 4 1922 – Dr V.R Mason names the disease Sickle Cell Anemia
  5. 5 1927 – Pathophysiology of Sickling Explained
  6. 6 1948 – The Protective Role of Fetal Haemoglobin
  7. 7 1949 – Sickle Cell Becomes the First Molecular Disease Discovered
  8. 8 1950s – Sickle Cell Trait and Protection from Malaria
  9. 9 1956 – Sickle haemoglobin sequenced
    1. 9.1 Diagnosis of Sickle Cell Disease
    2. 9.2 Newborn Screening
  10. 10 1977 -Sickle Gene Mapped
  11. 11 1980s – Penicillin Recognized as Preventative Medicine for Children with Sickle Cell
  12. 12 1984 – First Reported Cure for Sickle Cell: Bone Marrow Transplantation
  13. 13 1998 – FDA Approves the Use of the Drug Hydroxyurea to Treat Sickle Cell
  14. 14 1999 – Setback in Gene Therapy Jesse Gelsinger
  15. 15 2010 – 100th Anniversary of the Identification of Sickle Cell by Dr. Herrick 
  16. 16 References    

The Evolution of Sickle Cell

Sickle cell disease or sickle cell anemia is a hereditary genetic disease characterized by the presence of abnormal crescent-shaped red blood cells instead of the regular biconcave disc-shaped cells. Red blood cells transport oxygen from the lungs to various other organs and tissues with the help of a protein called haemoglobin. The main cause of sickle cell disease is when haemoglobin mutates into an abnormal type called haemoglobin S. The presence of Haemoglobin S causes red blood cells to be sickle-shaped and rigid, making it more difficult for them to flow through blood vessels in the body to deliver oxygen. Consequently, these sickled cells stick to the walls of various blood vessels, resulting in blocked blood flow that can lead to organ damage, pain and infections.


A healthy blood cell (right) compared to a sickled blood cell (left)
(Image from discovery.com)

1910 – First Description of Sickle-Shaped Blood Cells by Dr James Herrick

In 1904, Walter Clement Noel traveled from Grenada to the United States to start studying at the Chicago College of Dental Surgery.  A few months later he was admitted to the Presbyterian Hospital in Chicago when he developed severe respiratory distress and a leg ulcer, both of which we now know are symptoms of sickle cell. Dr Earnest E. Irons, the intern who was on duty that day, performed a routine blood test and a urine analysis for Noel and was the first to observed these “pear shaped, elongated” sickled blood cells. It was not until 1910 that Dr Herrick, the supervisor of Dr Irons, published his article describing these “peculiar elongated and sickle shaped red blood corpuscles in a case of severe anemia.”  This was the first documented and recorded case of Sickle cell in Western medicine.  

Dr Noel returned to Grenada in 1907 and ran his dental practice in St. Georges, the capital city, until he died at the age of 32 from the acute chest syndrome.  The original report can be found here.


Dr James B. Herrick
(Image courtesy of rushinperson.rush.edu

1917 – Genetic basis for SCD Dr. V. Emmel

The third case of Sickle cell was described in 1915 by Cook and Meyer in a 21-year-old woman.  Interestingly, blood samples from both the patient and her father, who displayed no symptoms, showed the sickling deformity of the red cells and three of her siblings had died from severe anemia.  These observations made by Dr Emmel suggested a genetic basis for the disease but also led to a period of confusion with the genetics of the disease. 

Haemoglobin

Approximately 5% of the population in the world carry mutations that results in the production of abnormal haemoglobin and the resulting diseases are termed haemoglobinopathies. Normal globin genes produce three types of haemoglobins:
Haemoglobin A (normal form that exists after birth), Haemoblogin A2 (a minor component comprising less that 3%) and Haemoglobin F (predominant during fetal development). Several clinically relevant abnormal forms are highlighted in the table below.


There are generally more sickle-cell trait carriers than individuals who suffer from sickle-cell anemia, but the dominance of the trait in certain areas of the world has led to about 300,000 infants born annually with major haemoglobin disorders.

Inheritance of Sickle Cell Disease

To develop sickle cell disease or sickle cell anemia, one has to inherit two copies from Haemoglobin S: one from the father and one from the mother. The parents who have the sickle cell trait (one mutated gene and one normal gene) will have no symptoms of the disease. They are known as carriers of the disease. So if both parents are carriers the chance of both parents passing down the abnormal gene to one of their children is 1:4. The diagram below shows the possible outcomes of genetic inheritance of the disease if both parents are carriers.

 
Following this initial observation, several decades of research was required to establish the relationship between the sickle trait and the disease due to the discrepancy between the number of predicted cases using Mendalian genetics and the actual number of patients with Sickle cell anemia. This discrepancy was later explained by the low life expectancy of children with sickle cell anemia as the majority of the sickle cell children were dying before those sampled in the surveys.  It is now well established that the sickling trait is hereditary and is passed on in a Mendalian fashion from parents to children.
 

1922 – Dr V.R Mason names the disease Sickle Cell Anemia


Dr Mason, who observed the fourth reported case of Sickle cell, was also the first to call the disease “sickle cell anemia” and to notice the similarities between the cases.  He also noted that all of these patients were black, inadvertently giving rise to the popular misconception that sickle cell originated from people of African origin.

There are two main theories put forward to explain the origin of the Sickle cell mutation.

  • Single Mutation Theory: A single mutation occurring in Neolithic times in the Arabian Peninsula was originally postulated where changing climatic conditions resulted in human migration to India, Saudi Arabia, and down to Equitorial Africa.  Evidence for this theory included the distribution of certain agricultural practices and anthropological evidence. Evidence from blood groups and other genetic markers appeared to agree with an origin in Equitorial Africa and subsequent diffusion of the gene to India, Arabia, and the Mediterranean by the East African slave trade.
  • Multiple Mutation Theory: The multiple mutation theory has recently gained considerablpee support via genetic studies with the use of special enzymes called restriction endonucleases. These enzymes recognize and cut DNA at scific sequences. By using these enzymes to cut DNA from a normal individual and an individual with a disease and by looking at the differences between the patterns scientists are able to identify variations in DNA that are inherited. The technique is known as restriction fragment polymorphism mapping. One of the first marker to be looked at was the Beta-globulin gene (the one mutated in SCA) where a difference in the cutting patterns were observed between normal beta-globin genes and the samples that came from SCA patients. These variations identified within the beta-globin gene gives support to the multiple mutation theory. Since there were 4 different mutations, it is believed that these arose at 4 different geographical locations in Africa Benin, Senegal, Central Africa and Cameroon. There’s a 5th mutation that is associated with Eastern provinces of Saudi Arabia and Central India. These observed differences suggest rather than originating from a single origin and spreading across the world that the beta-globin mutation arose at multiple geographical locations independently of each other.
The multiple mutation theory also refutes the misconception of African origin.

1927 – Pathophysiology of Sickling Explained

Hahn and Gillespie were the first to associate the red cell sickling to low oxygen and acidic conditions.  They were able to revert sickled cells back to their normal discoid shape by simply providing the cells with oxygen. Further experiments showed that, apart from oxygen, increased serum acidity also induced sickling of red blood cells. The increased serum acidity thus the decrease in pH seen in sickled cells can be accounted to several factors.  Reduced water content seen in these cells is a result of the changes in the concentration of potassium chloride (K+ Cl-) and ions such magnesium (Mg+2) as can be used to modulate these effects. The loss of KCl from the cells via several mechanisms is followed by an efflux of water out of the cells, resulting in cell sicking. Several experiments have shown that oral magnesium supplements can be used to reduce dehydration in patients. For more preventative measures refer to living with SCA section.

1948 – The Protective Role of Fetal Haemoglobin

The protective role of fetal haemoglobin (HbF) was discovered in the 1940s, when Dr. Janet Watson suggested a link between HbF levels and the presence of disease symptoms in 1948.  She observed that higher HbF levels in newborns kept them asymptomatic. Humans possess predominantly HbF in their fetal life but within 12 weeks after birth the production of HbF production is shut off and replaced by the production of adult haemoglobin HbA. It is now known that in some sickle cell patients this switch does not occur as efficiently, resulting in higher than normal HbF levels. These differences in HbF levels mark the differences between symptom manifestation where patients with higher HbF levels have a milder form of the disease. 

1949 – Sickle Cell Becomes the First Molecular Disease Discovered

Work from several scientists contributed to the discovery of Haemoglobin, the protein responsible for Sickle cell disease. In 1940 Irwin Sharman noticed a difference between the way light passed through sickled blood cells compared to normal cells.  Dr. Castle, a Harvard professor in Medicine, understood the implication of this finding: a change in the spatial orientation inside these sickled blood cells. In a chance conversation Dr. Castle mentioned this to Linus Pauling, a scientist, who worked extensively on haemoglobin ultimately resulting in the identification of the two different forms of haemoglobin present in people with sickle cell.  Pauling tested the haemoglobin samples from normal individuals, Sickle cell patients and people with Sickle cell trait using a technique called electrophoresis, which separated proteins based on their size and electrical charge. While normal individuals had haemoglobin of one type distinguishable from the haemoglobin from patients with sickle cell, the individuals with the sickle cell trait had both.  This was the first reported case where a change in protein structure was shown to be inherited in a Mendalian fashion.

1950s – Sickle Cell Trait and Protection from Malaria

Many of the studies that examined the association between the sickle cell trait and malaria stemmed from the question, “Why is the sickle cell trait maintained in such high frequency when the homozygous mutations (two genes with Sickle mutation) result in death?” One possible explanation was that the heterozygous trait (only one sickle gene) must be advantageous under certain conditions such as malaria.

The first associations between sickle cell anemia and protection from malaria were made in the early years of this decade. E.A. Beets, a British medical officer stationed in Northern Rhodesia (now Zimbabwe), observed the malaria parasite less frequently in the blood films of persons with sickle cell trait. A study done by Alison in 1956 concluded that people with sickle cell trait developed malaria less frequently and less severely than those without the trait.  This was the beginning of a long-standing controversy between the sickle cell trait and the protection from malaria mainly because several experimenters were unable to reproduce the data highlighted in Alison’s study.

Today it is accepted that the sickle cell trait offers some protection against malaria especially during early childhood. A very recent study on this can be found here. Several mechanisms are proposed and debated on, including selective sickling of cells infected with parasites more effectively being removed, inhibition of parasite growth due to the lower pH and reduced levels of potassium in sickled red cells, and increased endothelial adherence of parasitized red cells.

1956 – Sickle haemoglobin sequenced

Haemoglobin is an iron-containing protein that transports oxygen. There are two parts to this protein: 1) the heme component which consists of the iron and the globin component which consists of the globin protein. The heme groups were identical between HbA and HbS suggesting that the differences should be in the globin domain of the protein. Vernon Ingram and J.A. Hunt sequenced the sickled haemoglobin in 1956 to show that a single mutation in the protein causes Sickle cell disease. 

Diagnosis of Sickle Cell Disease

A number of diagnostic tests exist to determine whether an individual has sickle cell disease. These tests vary from being highly to minimally invasive, but all are accurate procedures in determining the presence of the sickle cell trait or disease in a patient. Early detection is important because it can help reduce the likelihood of the sickle cell anemia patients from suffering from bacterial infections, pneumonia and acute splenic sequestration crisis, all of which have a high mortality rate in the first 3 years of infant life. Methods of early detection range from newborn screening tests to amniocentesis, and once babies are found to be carriers of sickle cell disease or trait, they can be promptly treated with preventative antibiotics to avoid premature morbidity. Early diagnosis will also ensure the appropriate education is given to parents on how to manage the occurrence of sickle cell crises experienced by the child.

Newborn Screening

In certain countries, babies are routinely screened for various diseases, like sickle cell disease, via blood tests. These tests involve collecting a small sample of blood from the baby’s heel through a simple needle prick, after which the blood is later subjected to various tests that determine the presence of haemoglobin S and any other proteins indicative of sickle cell disease in the blood. These tests include the following:

  • Sickle Solubility Test: Used to screen for the presence of Haemoglobin S in the blood. A chemical is added to the blood that reduces the amount of oxygen present in it. Individuals older than 6 months who are carriers of the trait will have various amounts of haemoglobin S present, depending of the severity of the disease in the affected person. The lack of oxygen in the blood will cause the red blood cells affected by haemoglobin S to sickle and form S-related polymers.
  • Haemoglobinopathy: This method of testing involves a variety of tests used for screening, diagnosis, and confirmation of the disease. It subjects blood samples taken from the patient to a number of tests that isolate proteins in the blood based on their molecular properties. Blood proteins affected by sickle cell disease will have different properties than healthy blood proteins, and can therefore be isolated.
  • Haemoglobin Electrophoresis: Used to isolate haemoglobin S and SC. It uses citrus agar gel and cellulose acetate to expose the patient’s blood to an electric field. This field will separate various blood proteins from each other on a gel based on their electric charges. Since the electric properties of these proteins are known, one can look for the presence of proteins at specific areas of the gel to confirm the presence of haemoglobin S and SC.
  • Isoelectric Focussing: This method is more sensitive than electrophoresis. At birth, infants have large amounts of haemoglobin F. Those with the sickle cell trait find that their haemoglobin S levels rise as their haemoglobin F levels fall. The levels of these two variations of haemoglobin stabilize around the age of 2. Adult sickle cell carriers continue to produce regular haemoglobin A, while those with sickle cell anemia produce little to none of this haemoglobin variant. Each of these variants of haemoglobin have specific properties that allow them to be separated by isoelectric focussing. This method again requires the patient’s blood sample to be subjected to an electric field of a gel where the haemoglobin variants are separated by their electric charge. It is similar to electrophoresis but differs in the fact that the variants only migrate through a gel to a certain point (the isoelectric point, where the charge through the gel at that point equals the charge of the protein) rather than allowing the variants to arbitrarily migrate across the gel.
  • High Performance Liquid Chromatography: This method is also more sensitive than electrophoresis. It is a chromatographic technique that separates haemoglobin variants according to their unique characteristics and properties. One method, called fractionation, involves changing the conditions of the blood plasma so that proteins that are usually soluble in the liquid become insoluble and are precipitated out in clumps. This technique can be used to precipitate haemoglobin variants out of the blood plasma.

1977 -Sickle Gene Mapped

Development of DNA sequencing by Walter Gilbert and Frederick Sanger allowed the mapping of the sickle cell gene. DNA is made up of four different bases (these are the letters of the DNA alphabet A, T, C and G) and the genes coded in the DNA are identified (or read) by determining the order of these bases. The technique developed by Sanger and colleges allowed this ordered mapping of the bases using which the gene responsible for Sickle cell was mapped.
 

1980s – Penicillin Recognized as Preventative Medicine for Children with Sickle Cell

Loss of splenic function (see Disease complications and Treatment section for more information) makes Sickle cell patients more susceptible to bacterial infections, especially pneumococci which results in Pneumococcal meningitis. In the early 1980s, it was noted that these Pneumococcal infections can be prevented by prophylactic penicillin in early childhood and by pnewumococcal vaccines at later stages. Although with the rise of many pneumococci strains that are resistant to penicillin, these preventative measures might need to be replaced in the future. 

1984 – First Reported Cure for Sickle Cell: Bone Marrow Transplantation

The first reported case of using a bone marrow transplantation to cure sickle cell disease was performed on an 8-year-old girl that also had acute leukemia. The bone marrow of the girl with SS was successfully replaced with bone marrow of her AS brother. Since then, bone marrow transplants have been performed successfully on a number patients who were severely affected with sickle cell with over 90% survival and 74% event-free survival by 1997.
 
Bone marrow is the soft, fatty tissue that can be found inside bones and these tissues have stem cells that can give rise to red blood cells, white blood cells and platelets. In order to perform transplantations, the bone marrow of the patient is killed using either radiation, chemotherapy or both and is replaced by healthy donor bone marrow. More information on bone marrow transplants can be found here. Bone marrow transplantation is a high-risk procedure and can be life threatening. It is expensive and requires expert physicians, making it improbable to implement as a treatment in third world countries where sickle cell is a major health problem. Aside from these requirements, medical complications such as graft-versus-host disease (the newly transplanted bone marrow attatcks the transplant recipient's body) and graft rejection can result from bone marrow transplants. Because of this, bone marrow transplants are normally only offered as a treatment option to patients that are severely affected by sickle cell.

1998 – FDA Approves the Use of the Drug Hydroxyurea to Treat Sickle Cell

Much of the pharmacological research to treat sickle cell focused on drugs that would induce the production of fetal haemoglobin because of its protective role. The first drug to be tested in patients that showed an increase in fetal haemoglobin production was 5-azacytidine, but this drug was never tested in large-scale clinical trials because of suspected carcinogenic (cancer causing) effects. In experiments where rats were treated with 5-azacytidine, there were increased incidents of tumors. 

The next obvious choice was to find a drug with similar effects on HbF levels as 5-azacytidine and HU was one of these. The very first experiments with hydroxyurea were performed in anemic monkeys, followed by a successful study on just two patients that showed in increased in HbF levels after being treated with hydroxyurea. But to gain FDA approval, drugs need to prove success through multiple phases of clinical trials, so the preliminary studies were followed by many small scale clinical studies with both adults and children.  Once hydroxyurea was proven effective in these small scale studies it was then tested in a large multicenter clinical trial that involved 150 patients with sickle cell who were monitored for over a two-year period. The multicenter trial produced a positive outcomes leading to the approaval of hydroxyurea by the FDA as the first disease-modifying drug.  

A timeline of the growth in hydroxyurea research since the 1980s can be found here. 
 
The mechanism by hydroxyurea increases HbF levels is currently not very well understood. Inhibition of ribonucleotide reductase, an enzyme that is needed to produce nucleotides that makes up DNA, by hydroxyurea is thought to be the most important. By inhibiting the production of ribonucleotides, hydroxyurea essentially stops DNA synthesis and eventually cells will die because long-term exposure to hydroxyurea is toxic. Hydroxyurea also decreases the frequency of painful episodes, acute chest syndrome, need for transfusions and the number of hospital admissions for patients with sickle cell. Hydroxyurea is also favoured over other drugs because it can be taken orally and it has low toxic effects.

1999 – Setback in Gene Therapy Jesse Gelsinger

Because sickle cell anemia is caused by one defective gene, it is a good candidate for gene therapy. If the sickle cell gene can be replaced by a normal gene in the bone marrow, patients will be able to produce normal haemoglobin. Scientists have been exploring this option for several decades but the death of Jesse Gelsinger in 1999 was a major setback. Jessie was the first person to be publically identified to have died during a clinical trial involving gene therapy.
 
Gene therapy involves replacing the defective gene with a normal gene normally by injecting patients with a virus that has been genetically altered to carry normal human DNA. The virus is targeted to a specific cell type of patients and once the virus vector is there it unloads the genetic material containing the therapeutic gene which should produce normal proteins. More information on gene therapy can be found here.

Jesse had a rare genetic disease known as orinthine trascarbamlase deficiency. He had a defect in one gene whose protein product was required to breakdown ammonia, a by-product of protein breakdown. The adenoviral vector that was injected into Jesse resulted in a massive immunoresponse (the body recognized the virus as a foreign object and started attacking it) which resulted in multiple organ failure and brain death. The inquiry following his death revealed that many of the research team at the University of Pennsylvania had violated many of the protocols that should have been followed during his clinical trial. Detailed information can be found here.

2010 – 100th Anniversary of the Identification of Sickle Cell by Dr. Herrick 

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