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Rapid genetic disease screening possible using laser mass spectrometry

In 1993, using their new ability to detect 35 to 110 base pairs in a single DNA strand, Winston Chen and his associates at ORNL were the first to demonstrate the use of laser desorption mass spectrometry (LDMS) to detect a mutant gene responsible for cystic fibrosis (CF). Their demonstration used clinical samples custom prepared by Drs. Karla Matteson and Lan-Yang Chang, both of the University of Tennessee Medical Center (UTMC).

CF is an inherited, fatal disease in which mucus buildup promotes digestive disorders and bacterial infections in the lungs. Because each person with CF is the child of parents who both carry defective forms (alleles) of a particular gene, there is interest in large-scale screening to let people know their chances of having a child with CF.

"Our technique could be used to rapidly screen many people for a specific defect in a gene on chromosome 7 that causes 70% of all CF cases," Chen says. "The defect is the absence of three base pairs of DNA in both alleles that control production of CFTR, a protein that prevents mucus buildup. CF carriers have a single defective allele that may be passed on to their offspring, and people born with CF have two defective alleles.

The ORNL group was the first to show that LDMS can diagnose a genetic disease via DNA analysis. The technique, which is not yet used commercially, screens for CF in minutes, not hours, making it 10 times faster than conventional gel electrophoresis. Also, it does not use toxic chemicals or radioactive materials, which require costly methods of disposal.

In their continuing collaboration with Drs. Matteson and Nick Potter, also of UTMC, Chen and his colleagues demonstrated in 1996 that a single-base mutation (replacement of the right base with the wrong one) can be detected by LDMS.

More recently, he and Dr. Potter showed that LDMS can detect neurodegenerative diseases that result from dynamic mutations, such as Huntingdon Disease. The normal Huntingdon gene has 9 to 24 repeats of the GAC sequence. The mutant gene causing Huntingdon disease has more than 25 repeats. The researchers showed that LDMS can identify the HD gene because of its greater molecular weight, resulting from the many additional repeats.

"Laser desorption mass spectrometry," says Chen, "is emerging as a new tool for screening populations for various genetic diseases."

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