Biotechnology

Duchenne muscular dystrophymuscular dystrophy
Inherited condition which leads to the progressive weakening and breakdown of muscles. This in turn leads to increasing levels of disability. In its most severe forms it can be fatal. (DMD) is the most severe form of muscular dystrophy. It affects about one in every 3500 boys who are born – about 100 boys a year in the UK. It is a sex-linked genetic condition which means the boys cannot make a protein called dystrophin, a protein vitally important for maintaining healthy muscles. Without it the muscles weaken and waste away, being replaced by fat, so that by their early teens most affected boys are confined to a wheelchair and their life expectancy is only to early adulthood.

Duchenne muscular dystrophymuscular dystrophy
Inherited condition which leads to the progressive weakening and breakdown of muscles. This in turn leads to increasing levels of disability. In its most severe forms it can be fatal. is a sex linked recessive disease, inherited on the X chromosomechromosome
A chromosome is like a packet of coiled up DNA. Humans have 23 pairs of chromosomes. They are in the nucleus of every human cell.

The faulty gene is very large, which makes normal gene therapygene therapy
A new, experimental method of fighting disease by replacing a defective gene with a healthy gene. techniques difficult. However researchers in the United States and in Britain have found ways of using parts of a healthy gene, called mini-genes, to repair the damaged DNA, enabling the muscles to produce dystrophin and to function in a much more normal way. What is more, the effect has been long term – the protein was still being made a year after the gene was inserted. The only problem is that the gene therapy technique has so far only been tried in mice and golden retrievers, which have a natural mutationmutation
A change in the arrangement or amount of genetic material in a cell. similar to muscular dystrophymuscular dystrophy
Inherited condition which leads to the progressive weakening and breakdown of muscles. This in turn leads to increasing levels of disability. In its most severe forms it can be fatal. .

Much of this research depends on knockout mice. To produce knockout mice researchers genetically modify some embryoembryo
The name for a group of cells that are developing into a fetus. In humans this is from implantation to the 8th week of development. nic stem cellstem cell
Cells which can divide repeatedly without becoming differentiated and have the capacity to develop into a diverse range of specialised cell types. s to inactivate or ‘knock out’ a healthy gene. These cells are then injected into mouse embryos which are then implanted into a surrogate mother. The mice which result have some knockout cells and some normal cells, and they are then implanted to produce homozygoushomozygous
The description of an individual who has two identical alleles for one particular gene.  knockout mice.

Knockout mice often show changes in their phenotypephenotype
Set of observable traits of an organism. It is determined by the combination of an organism’s complete set of genetic material, or genotype, and the environment. which mimic human genetic problemsgenetic problems
Problems which are inherited. , helping scientists understand exactly what the gene does.

Knockout mice are also useful for studying the impact of different therapies. We have many of our genes in common – of 4000 genes studied in mice and humans, only ten of them are found in one species but not in the other. This, along with the fact that mice reproduce rapidly, have large litters, and are easy and cheap to keep means that knockout mice are incredibly useful in our search to understand gene functions and to find cures for many diseases.

Many of the current trials on possible treatments for DMD still involve the use of medicines to alleviate symptoms, but there have been some promising results recently with genetic modificationgenetic modification
An alternative term for genetic engineering/recombinant DNA technology. in both mice and dogs. A few phase 1 human clinical trials are in progress and more are expected soon. Some scientists are attempting to replace small regions of the faulty gene, others are trying to replace the whole thing. Gene therapygene therapy
A new, experimental method of fighting disease by replacing a defective gene with a healthy gene. has not yet been fully successful in overcoming any genetic diseases, so any patients who take part in early trials of a possible new treatment – and their parents – are very brave. New technologies such as CRISPR-Cas9CRISPR-Cas9
A genome editing tool, based on a bacterial system, which provides a precise, fast and relatively cheap method for manipulating the genome of an organism. hold out hope for new therapies including editing muscle-forming stem cellstem cell
Cells which can divide repeatedly without becoming differentiated and have the capacity to develop into a diverse range of specialised cell types. s rather than trying to change the whole organism. There is a long way to go, but muscular dystrophymuscular dystrophy
Inherited condition which leads to the progressive weakening and breakdown of muscles. This in turn leads to increasing levels of disability. In its most severe forms it can be fatal. is another disease where gene therapy may eventually result in a treatment or even a cure.

See:
Knockout Mice Fact Sheet, National Human Genomehuman genome
The complete sequence of all 20,000-25,000 human genes. That is, which chromosomes they are in and whereabouts the gene appears on that chromosome's piece of DNA. Research Institute
Why Mouse Matters, 2000 Mouse Sequencing Consortium, National Human Genome Research Institute
A new animal model of Duchenne muscular dystrophy, Muscular Dystrophy UK