Many of the most debilitating and deadly diseases are caused not by infection by bacteria or viruses, but by our own genes. These are called Genetic Disorders. If we could only rewrite those genes, there would be wonderful potential for treating all kinds of conditions. Though the challenges are enormous, the last couple of years have seen tremendous breakthroughs.
Each cell in our body contains a nucleus, into which are packed chromosomes consisting of strands of DNA (Deoxyribonucleic Acid).
The sequence of molecules in the DNA comprises the gene, the unit of heredity. DNA contains the instructions to create proteins which build into new cells, and by unravelling and duplicating itself, the double helix of DNA can pass on genetic information through reproduction.
See Also: DNA Testing For Genetic Conditions
If this genetic information is incorrect or damaged, the result can be genetic disorders such as Down syndrome, muscular dystrophy, haemophilia, sickle cell disease, cystic fibrosis, Crohn’s disease and many others—in fact around 6,000 genetic disorders are recognised.
These disorders can be caused by three types of genetic damage; to a single gene (sickle cell anaemia is an example); to a whole chromosome (for instance Down syndrome) or a complex disorder where there is mutation to two or more genes.
Since the structure of DNA was identified by Watson and Crick in 1953, scientists have been working to analyse the human ‘genome’, the complete genetic code, and to tackle the possibility of correcting mistakes.
Scientists keep track of genes by giving them unique names—for example, a gene on chromosome seven that has been associated with cystic fibrosis is called the Cystic Fibrosis Transmembrane Conductance Regulator, or CFTR.
But identifying errant genes and correcting them are two quite different things. How can we hope to make adjustments to such impossibly small molecules?
See Also: DNA Tests: Not Just For Television
In ‘gene therapy’, researchers typically do this using a virus to carry the corrected genetic cargo into the patient’s cells, because that’s what viruses evolved to do with their own genetic material.
Researchers are testing several approaches to gene therapy, including:
• Replacing a mutated gene that causes disease with a healthy copy of the gene.
• Inactivating, or ‘knocking out,’ a mutated gene that is functioning
• Introducing a new gene into the body to help fight a disease.
Gene therapy was first tested on humans in 1990 and can be performed inside or outside the body. When only certain populations of cells need to be ‘fixed’, doctors may inject the virus carrying the gene directly into the part of the body that has defective cells—for example part of the brain when treating Parkinson’s disease. This approach is also being used to treat eye diseases and haemophilia.
In out-of-the-body gene therapy, researchers take blood or bone marrow from a patient and separate out immature cells, then add an edited gene to those cells and inject them into the bloodstream of the patient; the cells travel to the bone marrow, mature and multiply rapidly, eventually replacing all of the defective cells. This would be used for instance in cases of sickle-cell anaemia and immune deficiency.
Gene therapy has its difficulties, as the viral hosts can cause side-effects, so at the moment It is being tested only for diseases that have no other cures. But researchers are working on ways to eliminate the side effects and consider the technique to be extremely promising.
See Also: The New Prenatal Test For Down Syndrome
From 2020, all seriously ill children in England with an unexplained disorder will be eligible for genome analysis, following a project at Addenbrooke’s Hospital and Cambridge University which found that one in four children in intensive care had a genetic disorder. Researchers were able to give a diagnosis within two to three weeks, which sometimes led to a change in treatment or spared children further invasive tests. So far, about 350 babies and children in intensive care at Addenbrooke’s Hospital have had their genome, made up of billions of letters of DNA code, analysed as part of the Next Generation Children research project.
Meanwhile Great Ormond Street Hospital (GOSH) and the Institute of Child Health (ICH) continue to lead the world in gene therapy, and together are responsible for more innovative gene therapy trials than any other centre worldwide. Seven of these trials have focused on primary immunodeficiencies.
Under the leadership of world-leading scientists Professors Adrian Thrasher and Bobby Gaspar, the gene therapy team have made extraordinary progress, particularly in pioneering new treatments for children born with weak or completely absent immune systems.
Despite their early success, the team know that more needs to be done. Over the next five to 10 years, Professors Thrasher and Gaspar aim to refine and develop their gene therapy techniques so that they can be used to help children with a wider range of life-threatening and life-limiting genetic diseases. These include some metabolic disorders and certain blood diseases.
Professor Gaspar says “We want to be able to deliver gene therapy for a whole wide range of conditions, not just the ones we started off with. Of course we want to build on that as well, but we want to treat far more diseases.
“We want to treat larger numbers of patients and not just patients at Great Ormond Street Hospital. We want to take this and make it a medicine that can be used in patients worldwide.” And Professor Thrasher adds: “With support, I believe that a decade further on, gene therapy will be able to improve the life and health of many children with life-threatening diseases, where other treatment methods are either ineffective or non-existent. It’s a very exciting time to be working in this field.”
To find out more about the DNA treatments that can treat Genetic Disorders, visit the page on the NHS website
This feature was originally published in the Winter edition of Live to 100 with Dr Hilary Jones, which you can read here.