Sickle cell disease, or SCD in short, refers to a group of inherited red blood cell disorders. In these patients, the hemoglobin protein present inside the red blood cells is abnormal, causing the RBCs to become rigid, sticky and “C” or sickle, shaped. The faulty hemoglobin is known as sickle hemoglobin (HbS), and is caused by a mutation. It is estimated that about 70,000 to 100,000 Americans have sickle cell disease.
Since the RBCs become stiff and sticky in the SCD patients, the blood flow to organs is blocked, damaging many organs including the lungs, kidneys, brain, liver, spleen, resulting in pain for patients. The disease can even lead to stroke or acute chest syndrome, and in some cases prove fatal. The average life expectancy for patients with sickle cell disease in the United States is approximately 40 to 60 years.
But despite having defective adult hemoglobin, in some people, the disease is less severe as they keep producing fetal hemoglobin throughout adulthood.
Fetal hemoglobin is produced during fetal life, and its concentration in the infant’s hemoglobin decreases after birth. By six months of age, fetal hemoglobin production is stopped and that of adult hemoglobin begins.
It is a well known fact that boosting fetal hemoglobin production can improve symptoms of sickle cell disease. Fetal hemoglobin (HbF) differs from adult hemoglobin in that it has a greater affinity for oxygen than does adult hemoglobin.
For more than 50 years, scientists have been trying to understand how the fetal hemoglobin gene is switched off so as to find a cure for inherited blood disorders like sickle cell disease and ß-thalassemia.
Now Australian scientists, led by professor Merlin Crossley of the University of New South Wales, have finally solved the mystery by identifying that the two genes called BCL11A and ZBTB7A switch off fetal hemoglobin gene by binding directly to it. They also found that by introducing natural mutations into erythroid cells, using genome-editing technology such as CRISPR-Cas9, the expression of fetal hemoglobin gene could be raised.
Although great strides have been made in understanding the mechanisms of sickle cell disease, the options are very limited when it comes to treatment.
Until July 2017, Hydroxyurea, approved in 1998, which also works by reactivating fetal hemoglobin production, was the only drug treatment option for SCD patients.
Endari, developed by privately-held Emmaus Life Sciences, became the first treatment to be approved for sickle cell disease in almost 20 years, when it was given the FDA nod last July. Another common method for treating SCD is blood transfusion.
The above mentioned options are only disease modifying therapies. Stem cell transplantation has proven to be the only curative therapy for SCD.
The first successful hematopoietic stem cell transplantation for sickle cell disease was performed in 1984, according to NCBI. A number of cases have since been documented across the globe.
As recently as April 4, 2018, it was reported that a 26-year old woman who underwent stem cell transplant at Calgary’s Tom Baker Cancer Centre, last November, has been cured of SCD. She is the first adult in Canada to be cured of this disease.
However, the curative approach has its own challenges because of the difficulty in finding a matching donor.
Now, let us take a look at some of the companies developing treatments for sickle cell disease.
by RTTNews Staff Writer
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