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Mahesh

25/11/23 12:15 PM IST

Sickle cell breakthrough

In News
  • The UK drug regulator last week approved a gene therapy for the cure of sickle cell disease and thalassaemia, seen as a landmark breakthrough by many.
  • This is the first licensed therapy in the world based on the gene editing technology Crispr-Cas9 that earned its innovators a Nobel Prize in 2020.
Working of therapy
  • Both sickle cell disease and thalassaemia are caused by errors in the gene for haemoglobin, a protein in the red blood cells that carry oxygen to organs and tissues.
  • The therapy uses the patient’s own blood stem cells, which are precisely edited using Crispr-Cas9. A gene called BCL11A, which is crucial for switching from foetal to adult haemoglobin, is targeted by the therapy.
  • Foetal haemoglobin, which is naturally present in everyone at birth, does not carry the same abnormalities as adult haemoglobin.
  • The therapy uses the body’s own mechanisms to start producing more of this foetal haemoglobin, alleviating the symptoms of the two conditions.
Sickle cell disease
  • The genetic error in sickle cell disease leads to red blood cells assuming a crescent shape.
  •  Unlike the disc shaped normal cells, the sickle-like cells cannot move around easily in the vessels, resulting in blocked blood flow.
  • This can lead to episodes of severe pain, life-threatening infections, anaemia, or a stroke.
  • An estimated 30,000-40,000 children in India are born with the disorder every year.
  • The symptoms manifest in people who inherit a pair of damaged genes from both parents.
  • Those who carry only one copy of the gene from one parent can lead a normal life.
  • This is the same as thalassaemia, in which people who inherit a pair of genes from both parents experience symptoms like severe anaemia.
Thalassaemia
  • Thalassaemia leads to low levels of haemoglobin, leading to fatigue, shortness of breath, and irregular heartbeats.
  • People with the condition need blood transfusions throughout their life. The transfusions also lead to accumulation of excess iron in the body, for which they need chelation.
  • India also has the largest number of children with thalassaemia major in the world — about 1-1.5 lakh.
Preparation of Therapy
  • Casgevy is a one-time treatment for which the doctor has to first collect blood stem cells from the bone marrow using a process called apheresis — used to filter out the blood for different components.
  • The cells are then sent to the manufacturing site where it takes about six months for them to be edited and tested.
  • Before a transplant with the edited cells, the doctor gives a conditioning medicine for a few days to clear the bone marrow of other cells that will be replaced by the modified cells.
  • The patient has to stay in hospital for at least a month so that the edited cells take up residence in the bone marrow and start making red blood cells with normal haemoglobin.
  • Side effects from the treatment are similar to those associated with autologous stem cell transplants, including nausea, fatigue, fever and increased risk of infection.
Challenges
  • Although the price of the therapy hasn’t been announced, it is likely to be very high.
  • Estimates suggest it could be as much as $2 million per patient, which is in line with other gene therapies.
  • Cost is one of the biggest limitations of newer gene therapies, along with the absence of local manufacturing facilities, which means that the harvested blood stem cells have to be sent across countries.
  • The prices will likely come down as more and more people work on it,.“Developing local manufacturing facilities will also help
Source- Indian Express

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