By David N. Leff
Editor's note: Science Scan is a roundup of recently published biotechnology-relevant research.
Two separate anatomical anomalies afflict babies born with cystic fibrosis (CF). One causes obstructive azoospermia - absence of spermatozoa in semen ejaculate. The other, meconium ileus (MI), or total blockage of the intestine, is more severe. MI is the first diagnostic sign of CF; it occurs in 15 percent to 20 percent of newborns with the disease.
CF is the most common single gene disorder in the world. It strikes one in every 2,500 neonates, and is largely limited to Caucasians of European ancestry. A decade ago, molecular geneticist Lap-Chee Tsui, at the University of Toronto, identified the CF gene - cystic fibrosis transmembrane conductance regulator (CFTR) - on the long arm of human chromosome 7.
Since then, upwards of 800 different mutations have been discovered on that gene, all causing variations in the disease. But one variation, MI, could not be traced to any of those gene aberrations. This and other CF hallmark disorders that couldn't be laid at the door of CFTR mutations have led scientists to suspect some unknown factors, perhaps other genes that somehow modified the effects of CFTR.
Now, Lap-Chee Tsui and his collaborators have tracked down one such genetic modifier, as they report in the June 1999 issue of Nature Genetics. Their brief communiqui bears the title, "Detection of a cystic fibrosis modifier locus for meconium ileus on human chromosome 19q13 [its long arm]." The paper lists 22 co-authors at 10 CF centers in six countries of Europe and North America.
Tsui's group previously had mapped the suspect cystic fibrosis meconium ileus gene (CFMI) to a region of mouse chromosome 7. This gave them a leg up on hunting it down in the human genome. The co-authors examined nine polymorphic satellite - DNA repeat - markers in 197 CF sibling pairs and parents from 161 nuclear families.
"Larger study populations will be required," their paper pointed out, "to refine the chromosome localization of CFMI in both humans and mice, so that systematic analysis of candidate genes will become feasible." It concluded, "Identification of modifier genes will ... provide insights into prognosis and management," presumably leading to development of novel therapies.
Azoospermia is a less dire CF defect, but packs a different genetic danger: the risk of passing on a CF gene mutation to future generations. More than 95 percent of CF men are infertile, owing to blockage or absence of one or more of the ducts and tubules involved in spermatogenesis. However, as a paper in the forthcoming issue of JAMA, The Journal of the American Medical Association, dated June 16, 1999, points out: "[M]any individuals with isolated obstructive azoospermia have rare or private mutations. Since the obstacle to conception for these men has been overcome by in vitro fertilization-intracytoplasmic sperm injection, decreasing the risk of passing pathogenic CFTR mutations on to the progeny is of paramount importance." The co-authors recommend, "This consequence may be avoided through clinical strategies such as genetic counseling and preimplantation or prenatal diagnosis."
CFTR's discoverer, Lap-Chee Tsui, is a co-author of the JAMA paper, which is titled: "Proportion of cystic fibrosis gene mutations not detected by routine testing in men with obstructive azoospermia."
Pocket-Size Kit Detects Nerve Gas On Site In Minutes, Vs. Days Or Weeks In Current Practice
Rich industrialized nations buy into the members-only nuclear weapons club. Poor, so-called developing countries have to make do with low-cost but highly lethal chemical or biological weapons. High on that low-tech list are the nerve gases, notably sarin, soman and VX. (See BioWorld Today, Nov. 6, 1996, p.1.; and Dec. 3, 1996, p. 1.)
"They all work the same way," explained molecular biologist/immunologist Kim Janda, who holds an endowed chair in chemistry at the Scripps Research Institute in La Jolla, Calif. "They attack the central nervous system, interact with the acetylcholinesterase neurotransmitter enzyme, and shut it off. Sarin, he recalled, "was implicated in attacks by Iraq on Kurdish communities and by the terrorists in the Tokyo subway system."
These nerve gases are internationally monitored. "To detect sarin at a suspected site," Janda told BioWorld Today, "such as inspecting potential poison gas production plants, is a difficult, time-consuming process. Until now the procedure has consisted of taking soil samples on location and analyzing them with complicated special equipment, usually in a distant laboratory."
He and his research group at Scripps now have come up with a pocket-size, sarin-spotting field kit, which can do the job in situ in half an hour or less. He reports this device in the mid-June 1999 issue of the twice-monthly, bilingual German/English applied-chemistry journal Angewandte Chemie International Edition. His paper's title is: "Monitoring chemical warfare agents: A new method for the detection of methylphosphonic acid [MPA]."
Sarin and the other nerve gases are highly unstable. Exposed to air or moisture, they rapidly deteriorate to MPA, which would serve as a telltale indicator of the chemo-weapons. "MPA is what all these nerve agents are made from or deteriorate to," Janda noted. But the MPA molecule has no antigenic epitopes that could be sniffed out by a programmed monoclonal antibody. His kit gets around MPA's immunogenic invisibility.
"With the kit out in the field," Janda related, "you can collect samples of water, dirt, whatever you want; say, swab a tabletop or desk. Then you mix it with a little cocktail consisting of dioxine and water to extract out any of the so-called organics.
"Next," he continued, "mix up this solution with a particular reagent we've developed, which reacts with phosphorus compounds, specifically MPA. It kind of pins a bull's eye on the MPA, and leaves some nice big immunogenic spikes on that molecule, allowing the antibody to go for it.
"So that's all there is to the kit," Janda pointed out. "Just a couple of reagents in bottles. Mix em up and read your colors - usually we use green. Or read it out by a plate reader in a high-throughput screen.Janda is now refining the kit's design "to make it a little bit faster, so it can do its work in seconds vs. the half hour or so it takes in its present configuration."
What led Scripps into this whole area of poor nation's chemo- and bio-weaponry, he explained, "was that I had a contract with a specific agency of the government - but I can't tell you which one."
As for anthrax, now a trendy bio-weapon, Janda allowed, "We do that type of stuff, too, but it's not being published right now." He observed that anthrax takes days or weeks to kill, but "if you breathed sarin, you'd probably be toast in less than minutes.