Clones may aid work on motor neuron disease
British researchers apply for licence to generate human brain cells.
The British scientist who created Dolly the sheep has applied for a licence to clone human embryos in the search for treatments for motor neuron disease. If approved, the research should give experts a far better picture of what happens to the dying brain cells that characterize this condition.
Ian Wilmut, of the Roslin Institute in Edinburgh, and his colleagues submitted their proposal today to the UK Human Fertilisation and Embryology Authority (HFEA). They hope to receive a decision early next year and could potentially begin cloning around April 2005.
Motor neuron disease, a range of related conditions including amyotrophic lateral sclerosis, also known as Lou Gehrig's disease, causes around 1,000 deaths in Britain every year. The brain cells that govern movement gradually die off, leaving sufferers paralysed but, usually, with their intellect intact.
The causes are still poorly understood, says Wilmut. Around 2% of cases are linked to mutations in a gene called SOD1, although experts are still unclear about how this triggers disease. And a further 8% of patients inherit their disease and therefore presumably have some other genetic predisposition.
In the family
The researchers plan to clone embryos using DNA from people who have inherited motor neuron disease. Stem cells, which have the potential to develop into any human cell type, would then be taken from these embryos and encouraged to develop into motor neurons.
The process would require two kinds of cell, Wilmut explains: a skin or blood cell from a motor neuron patient, which would be used to provide the DNA, and a human egg cell from which the original DNA had been removed. The latter would come from surplus eggs from in vitro fertilization (IVF) procedures.
By examining what happens to these cultured neurons, researchers will learn more about how they die, hopes Wilmut's collaborator Christopher Shaw, a neurologist at King's College London. "We're only beginning to understand the mechanisms, because motor neurons are really inaccessible," he says. "When a patient dies you're only looking at the very end of the process."
Culturing motor neurons through cloning offers a solution to this problem, says Brian Dickie of the UK-based Motor Neurone Disease Association. "What we don't have, and desperately need, is a way of studying human neurons as the disease progresses," he says. "If we can develop stem-cell lines, we can see what's going on in the early stages of the disease process."
The cell lines could also be a valuable resource for testing potential treatments for the disease, Shaw suggests. At present, it costs millions of dollars to test a single new drug in animal models. But by using cloned cells, researchers could, in theory, screen hundreds of thousands of candidates every year, at a cost of less than £20,000 (US$36,000).
That is some way in the future, Wilmut cautions. "Our objective is to understand the disease. We hope one day our work could lead to treatments, but that's not the current aim," he says. Such an understanding will be priceless, Dickie says. "It's 130 years since the disease was first characterized, and we still don't know what causes 97% of cases."
Meanwhile, sufferers are dying, most within just a few years of diagnosis, Dickie says. The physicist Stephen Hawking has survived for 35 years with the disease, but he has bucked the trend. "Only 10% live for a decade or longer," Dickie says. "The typical survival is two to five years."
Their hopes, and those of patients with other fatal diseases, may yet be frustrated by the slow pace of research. The cloning work is limited by the availability of egg cells, Wilmut explains. "Not everyone is willing to donate them, and some will be of poor quality," he says. "So it's pretty much one disease at a time."