Researchers at the Burnham Institute for Medical Research in La Jolla, California, have found that a mixture of human stem cells taken from embryos and fetuses delayed a fatal brain and nerve disease in mice.

They believe their findings have implications for victims of diseases such as Parkinson's, Alzheimer's and amyotrophic lateral sclerosis, also known as ALS or Lou Gehrig's disease.

The human embryonic stem cells were transplanted into the brains of mice bred with the equivalent of Sandhoff disease which causes children with it to have severe mental retardation and motor dysfunction; death usually occurs in infancy.

Dr. Evan Snyder and an international team of researchers have found the transplanted stem cells moved throughout the brain to take on the jobs of damaged neurons.

Sandhoff disease causes an inflammation that kills brain cells, and it is impossible to treat in part because of the blood-brain barrier, a molecular gateway that keeps many drugs out of the brain.

Mice typically develop symptoms by 90 days of age and die between 114 and 130 days, while children with Sandhoff rarely live beyond age 6.

Snyder's team used a mix of stem cells, taken from days-old human embryos left over at fertility clinics, and transplanted them into the brains of the mice and no tumours formed, the mice did not "reject" the foreign cells, and the treatment seemed to reduce inflammation.

The transplanted human cells migrated and integrated extensively throughout the brain, but did much more than replace brain tissue destroyed by the disease.

Some of the transplanted cells replaced damaged nerve cells and transmitted nerve impulses, offering the first evidence that stem cell-derived nerve cells may integrate electrically and functionally into a diseased brain.

They also boosted the brain's supply of the enzyme Hex, which is lacking in Sandhoff disease.

The researchers found in the treated mice that well-being and motor function was preserved and they lived 70 percent longer than untreated mice.

Although the disease ultimately returned, the researchers plan to try keeping the disease at bay by giving booster injections of the stem cells.

Sandhoff disease belongs to a class of genetic diseases called lysosomal storage diseases which affect one in 5,000 patients, mostly children.

It is often used to model an array of adult neurodegenerative diseases such as Parkinson's, ALS, and Alzheimer's.

Sandhoff is caused by a mutation in the gene for an enzyme called hexosaminidase or hex, which brain cells need to get rid of excess fatty material called lipids.

When the lipid levels build up, brain cells die; it is similar to Tay Sachs disease, and there is no treatment for either.

The study not only represents the first "multidisciplinary" use of stem cells against a degenerative disease, but also highlights the fact that in future, the most successful therapies, including those employing stem cells, will probably involve the use of multiple strategies and the stem cell may be the "glue" that ultimately holds these therapies together in an effective manner by virtue of its fundamental biology.

The researchers believe that their study may serve as a springboard for development into a clinical trial.

The study is published in the journal Nature Medicine.