DNA and Sequencing Technologies

DNA sequencing means a process of determining the arrangement of adenine, guanine, cytosine and thymine in a DNA molecule.

In the mid-70s, a scientist called Fred Sanger developed a sequencing method called Sanger sequencing. This discovery of DNA code allowed more basic scientific applications to take place such as translational applications, diagnostic testing and drug therapy.

Many years of scientists improvements enabled Sanger to sequence sections of DNA up to approximately 600 bases in length. It was difficult to sequence one small section of DNA at once because of the more time and high cost required. Massively parallel sequences approaches, which are the Next Generation Sequencing (NGS) method enabled scientists to sequence hundreds of thousands of fragments of DNA at the same time.

“Next Generation Sequencing” (NGS) connotes various approaches use to sequence DNA.

  1. Smaller fragments for sequencing are derived from a sample of DNA.
  2. The NGS technology is used to read at the same time sequence of bases in many fragments of DNA. The fragments sequenced at the same vary from hundreds to millions and that depends on the type of sequencing taking place.
  3. The base sequences taken from DNA are generated in the form of a computer file. Each individual length generated from the original DNA fragment measures between 50-300 bases long, it is called, “read”.
  4. There is a specific program analyses the reads and matches specifically to the genome they arose from. This is what is called “alignment” or “mapping”.
  5. Variation between the sample DNA and the reference DNA are checked.
  6. Lastly the effect that a genetic variant will have on a protein is assessed. This is called “variant annotation”.

It is possible to sequence the whole of human genome quickly using these approaches. Many applications of NGS have been tried to find a specific genetic variant relevant to a specific disease but it has proved difficult. However, various methods have been devised which allow sequencing smaller regions of the genome. It allows sequencing just the portion of the genome that is likely to yield the relevant variation. This method is known as the “target enrichment” “capture” technique.


Gene Therapy for Diseases


Over the past two decades, there has been a tremendous advancement in Gene Therapy. Since the first attempt of modifying human DNA in 1980 till now, several trials have been conducted while many are still underway to ensure that any gene therapy that is brought into the clinic is safe as well as effective. Some of the most successful advancements of Gene therapy for diseases are:

  1. Severe Combined Immune Deficiency (SCID):

This deadly genetic disorder known the SCID was one of the first genetic disorders to be treated successfully with gene therapy, proving that the approach could work.

  1. Chronic Granulomatus Disorder (CGD):

CGD is a genetic disease that affects the immunity of the patients. It is basically the disease in the immune system that takes away the patient’s ability to fight against microbial infections that can be dangerous. The Gene Therapy enabled the reconstitution of the immune systems providing protection against bacterial and fungal infections.

  1. Hereditary blindness:

Gene therapies are being developed to treat varied types of inherited blindness, especially the degenerative forms. The years long research shows that gene therapy has the potential to slow or even reverse vision loss.

  1. Haemophilia:

Haemophilia is a disease where the blood does not clot and the patent suffer from continuous bleeding that can be fatal. This happens because the protein that helps the blood form clots is missing. In a small trial for the cure by gene therapy,the researchers successfully delivered a gene for Factor IX, the missing clotting protein, to liver cells.

  1. Cancer:

There is a wide variety of cancers and thus, multiple gene therapy strategies have been evolved to cure them. Among the thousands of gene therapy trials, 2/3rds have been made to treat cancer and several of these are already in their advanced stages.

  1. Neurodegenerative Diseases:

There has been the recent advancement in Gene Therapy for the treatment of brain related diseases such as Parkinson’s and the Huntington’s disease. This is basically the loss of the cells in brain that produce the signalling molecule dopamine and the patient loses the ability to control movements. The Gene therapy allows introducing such genes into cells in a small area of brain and provides improved muscle control to the patients.

A Possible Cure for Zika virus

Zika virus has turned out to be deadly for almost all of South America. More than 2,500 babies have been diagnosed with it while there is a medical emergency being imposed. Many women are asked not to get pregnant or take immediate steps towards safety for better health. As the global health organizations work around a solution, which can help cure this epidemic, gene editing has some answers that can be applied.

In general, female Aedes aegypti mosquitos are the one that carry the disease, if gene editing techniques such as the Crispr-Cas9 can be applied in changing their sex, epidemics can be cured. Two US scientists have studied the potential. If successful, it may be used to cure malaria, dengue and other mosquito related infections and diseases which turn out to be deadly. Although in its initial tests, the experiments may need considerable time may be years to complete. The World Health Organization has already asked for bolder and innovative means to fight such diseases, specially Zika virus and Genetic modification can be one area that can bring in some insights. Another innovative idea is y using gene drive technology. It can help create anew generation of mosquitoes that carry malaria, which does not have the host plasmodium parasite that kills a child every minute in Africa.

Dr. Zach Adelman from the Virginia tech thinks this process of Crispr-Cas9 can help infuse a genetic modification in females, which can help turn them into having male characteristics. The gene drive technology can also be sued to kill female mosquitoes, hence reducing the overall risk of diseases. There were more than 214 million Malaria cases in Africa alone last year, such technologies and innovative breakthroughs have now become the necessity of time.

Gene Editing to help manage Muscle disorder

Recently, Gene editing has seen growth with the use of the well-renowned Crspr-cas9 therapy. It includes using genes to replace damaged cells in DNA, helping cure the diseases. After a lot of luck and hope, researchers are trying to use it on a more intense disease, which affects boys at birth. Duchenne Muscular Dystrophy is deadly, can let boys loose muscle really fast and putting them in a wheelchair by the age of 10, it can result in heart failure and death.

Although it has not yet been tested on humans, three researchers reported to the Science journal that they used the therapy on mice. They used a virus that helps infect the mice while attaching with the DNA to cure the dystrophin gene. The defective stretch of DNA that affects the gene is known as anexon. With exon removed or not present, mice were able to regain muscle strength while shortening dystrophin protein helped mice retain health faster. The team comprised of Amy J. Wagers from Harvard University, Eric N. Olson from Univerity of Texas and Charles A. Gersbach from Duke University.

The affected genes mostly comprise of 79 exons or sections, but can also function if there are fewer than these exons present. Unless the two ends are intact, the protein will keep on functioning. Dr. Oslon thinks in order to help this work on humans, more clinical trials are needed and may take a few years before the issues related to permissions in regards to gene editing is provided. It needs to be safe, right and be standardized for humans in order to avert any damages. Although patients may receive e a single dose of treatment, Dr. Gersbach thinks it may take several before the protein is eliminated and the DNA becomes resistant. As current chemical drugs are not helping cure this disease, gene editing is seen as the future to ensure the safety of affected patients.