Health: Gene therapies are available on the NHS

Repairing or replacing these genes with 'good' ones, however, could solve - or at the very least treat - the problem, and this is what the emerging science of gene therapy is all about.

It was first suggested in the early-1970s that using 'good' DNA (genes are short sections of DNA) to replace defective DNA could treat inherited diseases, and since then scientists have been trying to work out how to do it, both for inherited conditions and many others.

The British Society for Gene and Cell Therapy (bsgct.org) says the first approved human gene therapy took place in 1990, on four-year-old Ashanti DeSilva who had ADA-SCID - an inherited disease that prevents normal development of the immune system. The therapy made a huge difference, meaning the little girl no longer needed to be kept in isolation and could go to school.

"When the human genome was mapped nearly 20 years ago, the notion that it could potentially unlock therapies capable of fixing genes responsible for some of the world's most devastating diseases was an idea of the future," says gene therapy expert Professor Bobby Gaspar, speaking on behalf of Jeans for Genes Day, the annual campaign for Genetic Disorders UK (geneticdisordersuk.org).

"We are at the forefront of a new era of treatment for genetic diseases using gene and cell therapies. Some of these are one-time, potentially curative investigational therapies that could provide life-changing benefits to patients and their families."

Gaspar says there are currently more than 10 cell and gene therapy products approved in the EU, ranging from products that treat cancer to rare immune deficiencies. A number of these are approved in the UK and available on the NHS in specialised centres, and with nearly 3,000 clinical gene therapy trials underway worldwide, the number of available treatments is expected to grow significantly over the next few years.

Here, Gaspar - a professor of paediatrics and immunology at the UCL Great Ormond Street Institute of Child Health and chief scientific officer at Orchard Therapeutics, a gene therapy company that seeks to permanently correct rare, often-fatal diseases - outlines five of the ways gene therapy can cure, stop, or slow a disease...

1. Cancer

"A variety of efforts are underway to use gene therapy to treat cancer. Some types of gene therapy aim to boost the body's immune cells to attack cancer cells, while others are designed to attack the cancer cells directly. One way the body protects itself from cancer is through T-cells, a main component of the immune system. But some cancers are good at avoiding these protection mechanisms," says Gaspar.

"Chimeric antigen receptor, or CAR T-cell therapy, is a new form of immunotherapy that uses specially altered T-cells to more specifically target cancer cells. Some of the patient's T-cells are collected from their blood, then genetically modified to produce special CAR proteins on the surface. When these CAR T-cells are reinfused into the patient, the new receptors help the T-cells identify and attack cancer cells specifically and kill them."

2. Vision

"There are more than 250 genetic mutations that can lead to a type of blindness called inherited retinal diseases, or IRD. People with a defect in the RPE65 gene start losing their vision in childhood. As the disease progresses, patients experience gradual loss of peripheral and central vision, which can eventually lead to blindness. Gene therapy for some IRD patients became available in 2017, delivering a normal copy of the RPE65 gene directly to the retinal cells at the back of the eye using a naturally-occurring virus as a delivery vehicle."

3. Movement

"For children with the genetic disorder spinal muscular atrophy, or SMA, a rare muscular dystrophy, motor nerve cells in the spinal cord are damaged, causing patients to lose muscle strength and the ability to walk, eat or even breathe," says Gaspar.

"SMA is caused by a mutation in a gene called SMN which is critical to the function of the nerves that control muscle movement. Without this gene, those nerve cells can't properly function and eventually die, leading to debilitating and often fatal muscle weakness. Researchers recently developed the first US-approved gene therapy to treat children less than two years of age with SMA. The therapy is designed to target the cause of SMA by replacing the missing or nonworking gene with a new, working copy of a human SMN gene, helping motor neuron cells work properly."

4. Infectious diseases

"Researchers believe targeted gene therapy and gene editing may have widespread application for a range of infectious diseases that aren't amenable to standard clinical management, including HIV. Although HIV isn't a hereditary disease, the virus does live and replicate in DNA," Gaspar explains. "Another early but encouraging approach uses a gene editing technology combined with a new long-acting, antiretroviral treatment to suppress HIV replication and eliminate HIV from cells and organs of infected animals.

"Gene editing is an approach that precisely and efficiently modifies the DNA within a cell. In this approach, gene editing can 'knock out' a receptor called CCR5 on immune cells used by HIV to enter and invade cells. Without CCR5, HIV may no longer invade and cause disease."

5. Rare diseases

"One approach being investigated for a number of rare, often-fatal diseases uses gene-modified blood stem cells with a goal of permanently correcting the underlying cause of disease. Blood stem cells are taken from the patient, and corrected outside the body by introducing a working copy of the gene into the cells. The gene-corrected cells are then put back into the patient to potentially cure the disease.

"Gene-modified blood stem cells have the capacity to self-renew and, once taken up in the bone marrow, can potentially provide a lifelong supply of corrected cells. Because of their ability to become many different types of cells in the body, this approach has the potential to provide a lasting treatment for many different severe and often life-limiting inherited disorders, many of which have no approved treatment options available," says Gaspar.

"For instance, ADA-SCID, sometimes referred to as 'bubble baby syndrome', is a disease where babies lack almost all immune protection, leading to frequent and devastating infections. Left untreated, babies rarely live past two years of age. Standard treatment options are not always effective or can carry significant risks. In 2016, the European Medicines Agency approved Strimvelis, a blood stem cell gene therapy for the treatment of ADA-SCID. Strimvelis was the first approved ex vivo gene therapy product in Europe.

"Jeans for Genes Day helped fund some of the earliest work using this type of gene therapy at Great Ormond Street Hospital in 2002, when Rhys Evans, a little boy with SCID, became one of the first children worldwide to be treated by gene therapy."

Jeans for Genes Day aims to raise money for children with life-altering genetic disorders by asking people to donate money for wearing jeans to work, school or wherever they like, on any day between September 16-20. Visit jeansforgenesday.org.