Cystic fibrosis gene guards against typhoid-study
10:43 a.m. May 06, 1998 Eastern

LONDON, May 6 (Reuters) - Cystic fibrosis may be one of the most common hereditary diseases because carriers of the faulty gene have an enhanced natural resistance to typhoid, U.S. doctors said on Wednesday.

The finding could explain why the defective gene is passed on to subsequent generations and may help in the search to develop a vaccine against the chronic lung disease.

``Defective genes are usually not maintained from generation to generation unless they offer some kind of survival advantage. It now appears that a likely benefit of carrying one defective cystic fibrosis gene is better resistance to typhoid fever,'' Dr Gerald Pier, of the Brigham and Women's Hospital in Boston, Massachusetts, said in a statement.

Cystic fibrosis occurs when a child has two defective copies of the gene, one from each parent, that encodes a protein known as cystic fibrosis transmembrane conductance regulator (CFTR).

Abnormal levels of CFTR block the movement of chloride ions and water in the lungs, gastrointestinal tract and other tissues and causes them to secrete large amounts of mucous.

As the mucous accumulates the children become increasingly susceptible to respiratory infections. Normal CFTR protein acts as a receptor for a bacterium that causes infection and clears it from the lung. But when CFTR is mutated or missing it if ineffective against it.

Pier and his team showed that normal CFTR protein is also a receptor for Salmonella typhi, a gastrointestinal agent that causes typhoid fever.

The finding could be important in vaccine research because when S.typhi is stripped of its ability to cause disease it is a good tool to deliver vaccines in the body.

AIDS researchers recently began a trial of an experimental vaccine composed of a weakened form of S.typhi into which a gene for a human immunodeficiency virus (HIV) protein had been inserted.

``Our work provides an understanding of how S.typhi gets into the tissues of the host's immune system,'' Pier explained. ``By manipulating S.typhi or other organisms to deliver antigens via the CFTR-uptake pathway, we may be able to develop better vaccines.''

Approximately 2,500 babies are born with cystic fibrosis each year in the United States and an estimated 12 million people carry the gene for the childhood illness.

Before the 1950s victims of the disease lived only a few years, but medical advances and better ways of controlling the disease has pushed the average lifespan of sufferers to about 30 years. ^REUTERS@

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