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Thursday, June 4, 1998 Published at 20:52 GMT 21:52 UK


'Gene surgery' for sickle cell anaemia

Street scene in the Kenyan capital, Nairobi: sickle cell anaemia affects millions in tropical Africa

Scientists in the USA plan to use a new type of genetic therapy to treat sickle cell anaemia, the incurable genetic disease that affects millions of people in tropical Africa and people of African descent around the world.

The red blood cells of people with sickle cell disease contain an abnormal type of haemoglobin, a protein that carries oxygen throughout the body.

A tiny defect in the protein distorts the red blood cells, resulting in blocked blood vessels, severe pain, anaemia and damage to kidneys, lungs and liver.

There is no cure for sickle cell anaemia and attempts to develop gene therapy for the disease so far have run into problems.

New technique

The new approach being developed at Duke University in North Carolina involves a new kind of gene therapy that is really a type of genetic surgery.

Conventional techniques attempt to replace defective genes where they sit on the DNA - the large molecules in the nucleus of a cell that carry all inherited information. In contrast, the approach adopted by the Duke team alters the faulty genetic information once it has been transferred to the area of the cell where proteins are made.

The secret to their strategy is the use of ribozymes, special enzymes that can find and cut out specific sections of the genetic code, and splice in new information.

These molecular scissors are part of the human body's natural gene-repair mechanism.

Writing in the journal Science, Bruce Sullenger from the Duke's Medical Centre said: "We have shown for the first time that it is possible to correct a genetic defect in blood extracted from patients for experimentation, not just in laboratory-grown cells.

"If we could get even 10% to 20% correction of the defect, it could make a huge difference for patients."

Future prospects

The treatment looks promising, but still has some distance to go before it can be used in human trials.

Nevertheless, the success of the laboratory work has clearly raised expectations. A pharmaceutical company has already been formed to develop the use of ribozymes to treat cancer and infectious diseases as well as sickle cell anaemia.

The gene that causes sickle cell anaemia is recessive. Those with two copies of the gene suffer the severest effects; those with a single copy, paired with a normal gene, suffer with only mild anaemia.

Ironically, this gives them a degree of protection against malaria because fewer normal red blood cells are available to the parasites for infection.

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