By David N. Leff

Several centuries ago, seafarers set sail from the west of England and made their first landfall on the shores of Newfoundland. They also touched at the Carolinas.

Other mariners put out from Spain or Portugal and landed in Costa Rica.

These ships did not export pathogenic viruses or bacteria to the New World. Rather, their crews brought with them a fatal human gene.

Rose Mary Boustany, a pediatric neurologist at Duke University, in Durham, N.C., construed this annal of medicine from her studies of Batten's disease. This neuron-wasting affliction strikes its preschool toddler victims blind, mute, bedridden and seizure-prone, then takes their lives in their teens or earlier.

Supporting her historic reconstruction, Boustany told BioWorld Today, "There's a large collection of Batten cases in the western part of Newfoundland, where those sailors first landed. And isolates in Costa Rica and South America."

British pediatric ophthalmologist Frederick Batten (1865-1918) described the disease that bears his name in 1903. He maintained, against much contrary opinion, that this lysosomal storage disease is entirely different from the better-known Tay-Sachs disease, which traces its ethnic inheritance back to Jewish communities in Eastern Europe.

"You can find Batten's disease in almost any ethnic group," Boustany pointed out, "but we don't have any Jewish or black children."

Until now, pediatricians have lumped together four variants of Batten's — infantile, late infantile, juvenile and adult, which vary in their age of onset and death.

The current issue of Science, dated Sept. 19, 1997, reports discovery of the gene for one of these four types in a paper titled: "Association of mutations in a lysosomal protein with classical late-infantile neuronal ceroid lipofuscinosis [LINCL]." Its first author is molecular biologist David Sleat, at Rutgers University's Center for Advanced Biotechnology and Medicine, in Piscataway, N. J.

"LINCL is an autosomal recessive genetic disease," Sleat told BioWorld Today.

Ceroid and lipofuscin are the two insoluble protein-lipid granules that build up in the neuronal lysosomes of LINCL for lack of the key enzyme needed to break them down. In this respect all four Batten diseases resemble Tay-Sachs, Gaucher's and other lysosomal storage diseases.

Enzymes Salvage Junk Molecules In Organelles

Lysosomes, which swarm in the cells of the body, Sleat explained, "are recycling organelles, where macromolecules are broken down by enzymes, and the resulting byproducts re-used to synthesize new molecules. These enzymes," he added, "are themselves synthesized in the cell's endoplasmic reticulum, then transferred from the Golgi apparatus to the lysosome by two receptors for mannose-6-phosphate. This is a sugar that acts as a targeting signal for lysosomal enzymes. Its receptors help direct the enzymes to the lysosomes in the brain's glial cells. (See BioWorld Today, Sept. 4, 1997, p. 1.)

The normal brain contains 50 or more such garbage-crunching lysosomal proteases, which show up as spots on two-dimensional gels.

"We used that carbohydrate modification," Sleat continued, "the mannose-6-phosphate, to look at lysosomal enzymes in LINCL patients compared to normal controls. We saw that one of those proteins that contains mannose-6-phosphate was missing. By isolating and sequencing this absent enzyme, and comparing it to known genes and proteins, we put together a near-complete sequence for the gene and mapped it to the short arm of human chromosome 11."

What causes the massive neuronal death that marks LINCL and the other Batten pathologies?

"As many as 50 or 60 percent of the brain's neurons may die as the disease progresses," observed co-author Raju Pullarkat. "One possibility is that the accumulation of undigested proteins may harm these neurons, which don't divide as other cells do."

The newly described gene, CLN2, Pullarkat observed, "codes for a type of enzyme that has never before been described in humans or other mammals. Nonetheless, it appears to be one of the most common protein-degrading enzymes in the brain."

Molecular biologist Peter Lobel, who heads the laboratory of protein targeting at the Rutgers center, is the Science paper's senior author. He remarked that "this is the first time researchers have used the mannose-6-phosphate strategy to identify a defective gene. For LINCL, it proved faster than positional cloning, which is commonly used to identify which of the body's 100,000 genes are defective."

Sleat said his team "is, at the moment, finished the fine gene structure of CNL2, and cataloguing mutations in a larger population of patients. We'll know how many base pairs it has in a few weeks."

Diagnostic, Therapeutic Payoffs In Offing

Prenatal diagnosis for LINCL, Sleat observed, "is certainly possible. Now that we've identified the gene and are mapping mutations, we might know where to look." He suggested that a more likely approach than testing fetal cells would be "in screening the siblings of patients, to see if they are potential carriers for the disease."

As for therapeutic intervention, he questions gene therapy or even enzyme replacement (as in Gaucher's disease) "because the primary lesion appears to be in the brain, and the blood-brain barrier makes it difficult to express or deliver a protein there."

But, he added: "It's quite possible that once we know what's going on, the way will open up for pharmacological intervention."

"Although LINCL is a rare disorder," Boustany said, "working out exactly how the gene works may enlighten us about neurodegenerative processes in a lot of other diseases, such as Alzheimer's, Parkinson's and a whole slew of such inherited disorders, including some of the lysosomal storage ones."

Extrapolating from pediatric Batten's to geriatric disorders is not as far-fetched as it may seem. Those ceroid lipofuscin pigmented proteins are known as "age pigments." Undetectable in children, they first appear at about age 20, and account for five to ten percent of cardiac muscle fibers by age 80.

Though rare, the Batten diseases are so horrendous they command much basic research and vigorous family support.

"We know, for example," said Boustany, "that the parent association in the U.S. lists about 700 affected families, of which half have the late infantile type." *