Gary Hsich, Kimbra Kenney, Clarence J. Gibbs, Kelvin H. Lee, Michael G. Harrington
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There is no practical and reliable premortem test for Creutzfeldt-Jakob disease and the related transmissible spongiform encephalopathies. Two proteins, designated 130 and 131, which have been detected in low concentrations in cerebrospinal fluid from patients with Creutzfeldt-Jakob disease, appear to be sensitive and specific markers for the disease. Attempts to identify these proteins, however, have been unsuccessful. We hypothesized that they may be present in the normal brain.
Methods. We detected proteins 130 and 131 in normal human brain, partially sequenced their amino acids, and found that they matched the brain protein known as 14-3-3. We then developed a simple, rapid immunoassay for this protein and tested it in cerebrospinal fluid samples from 71 humans and 30 animals with spongiform encephalopathies and in control samples from 186 humans and 94 animals.
Results. The immunoassay detected the 14-3-3 protein in cerebrospinal fluid from 68 of the 71 patients with Creutzfeldt-Jakob disease (96 percent; 95 percent confidence interval, 92 to 99 percent). Among 94 patients with other dementias, the specificity was 96 percent. If one excludes the three patients with dementia who had had strokes within one month before testing, the specificity was 99 percent. The test was positive in 12 of 24 patients with viral encephalitis. In animals the sensitivity of the assay was 87 percent and the specificity was 99 percent.
Conclusions. In patients with dementia, a positive immunoassay for the 14-3-3 brain protein in cerebrospinal fluid strongly supports a diagnosis of Creutzfeldt-Jakob disease. This finding, however, does not support the use of the test in patients without clinically evident dementia. (N Engl J Med 1996;335:924-30.)
From the Laboratory of Central Nervous System Studies, National Institutes of Health, Bethesda, Md. (G.H., K.K., C.J.G.), and the Biology Division, California Institute of Technology, Pasadena (K.H.L., M.G.H.). Address reprint requests to Dr. Gibbs at the Laboratory of Central Nervous System Studies, Basic Neurosciences Program, Division of Intramural Research, Bldg. 36, Rm. 4A05, 9000 Rockville Pike, Bethesda, MD 20892-4122, or to Dr. Harrington at Mailstop 139/74, California Institute of Technology, Pasadena, CA 91125.
1) Identification of 14-3-3 proteins in human platelets: effects of synthetic peptides on protein kinase C activation. Biochem J 315 ( Pt 1): 41-7 (1996) 2) Activation-modulated association of 14-3-3 proteins with Cbl in T cells. J Biol Chem 271: 14591-5 (1996) 3) Association of a 14-3-3 protein with CMP-NeuAc:GM1 alpha 2,3-sialyltransferase. Biochem Biophys Res Commun 224: 103-7 (1996) 4) Isolation and characterization of a cDNA from Trichoderma harzianum P1 encoding a 14-3-3 protein homolog. Gene 171: 123-7 (1996) 5) Function of 14-3-3 proteins [letter] Nature 382: 308 (1996)
The transmissible spongiform encephalopathies, or prion diseases, are neurodegenerative conditions that affect both humans and animals. They are transmissible experimentally both within and between mammalian species by inoculation with infected tissues and sometimes by ingestion in food. The diseases affecting humans have traditionally been classified as Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker disease, and kuru. They are rare, affecting about one person per million worldwide per year. By contrast, the prototypic spongiform encephalopathy scrapie is a relatively common, naturally occurring disease of sheep and goats, recognized for well over 200 years and occurring in many countries. Although these diseases have long been of biologic interest because of the unique properties of the infectious agent, the epidemic of a newly recognized prion disease, bovine spongiform encephalopathy, or "mad cow disease," among cattle in the United Kingdom and to a lesser extent in other countries has led to fears that transmission to humans could occur through the ingestion of infected tissues.
The human diseases occur in inherited, acquired, and sporadic forms. Around 15 percent are inherited, with an autosomal dominant pattern of inheritance, and are associated with coding mutations in the prion-protein gene. Acquired prion diseases include kuru and iatrogenic Creutzfeldt-Jakob disease. Kuru reached epidemic proportions among the Fore linguistic group in the eastern highlands of Papua New Guinea and was transmitted during cannibalistic rituals. Since the cessation of cannibalism in the 1950s the incidence of the disease has declined, but a few cases still occur as a result of the long incubation period in this condition. Recognized iatrogenic routes of transmission are treatment with human cadaveric pituitary-derived growth hormone or gonadotropin, dura mater or corneal grafting, and use of inadequately sterilized neurosurgical instruments. The large majority of prion diseases, however, occur in the form of a randomly distributed illness of unknown cause -- sporadic Creutzfeldt-Jakob disease.
Classic Creutzfeldt-Jakob disease, which may be familial, presents as a rapidly progressive dementia with myoclonus and is usually associated with the presence of characteristic pseudoperiodic sharp-wave complexes on electroencephalography. There is a rapid decline to akinetic mutism and death, often within three to four months. Cerebellar ataxia, extrapyramidal features, cortical blindness, and pyramidal signs are also frequently present. The results of routine laboratory investigations and examination of cerebrospinal fluid are usually normal. Neuroimaging is essential to rule out other conditions but cannot be used to make a definitive diagnosis. Clinically typical cases with a characteristic electroencephalogram will nearly always be confirmed as Creutzfeldt-Jakob disease at autopsy with the demonstration of the classic histologic triad of spongiform vacuolation (affecting any part of the cerebral gray matter), astrocytic proliferation, and neuronal loss. In about 5 percent of cases these changes are accompanied by the deposition of amyloid plaques. Atypical cases of Creutzfeldt-Jakob disease are, however, well recognized and may present diagnostic difficulties. Analysis of the prion-protein gene is important even in patients with no family history of prion disease. It may be diagnostic and used for presymptomatic testing in affected families (1,2); it has revealed a wider disease spectrum than hitherto realized. (3,4) There can be wide phenotypic heterogeneity within a family; therefore, a history of any neurodegenerative or neuropsychiatric illness is potentially indicative of inherited prion disease. (3)
Genetic susceptibility is also relevant to both the sporadic and iatrogenic prion diseases. There is a common polymorphism of the human prion protein, in which either methionine or valine is present at residue 129. Approximately 38 percent of whites are homozygous for the more frequent methionine alleles, 51 percent are heterozygous, and 11 percent are homozygous for the valine allele. The large majority of cases of sporadic Creutzfeldt-Jakob disease occur in persons who are homozygous for either allele (5); similarly, most patients with iatrogenic disease due to treatment with cadaveric pituitary-derived growth hormone are homozygous, with most homozygous for the valine allele. (6) However, although the protective effect of heterozygosity for the prion-protein gene (which is also seen in some inherited prion diseases) has been important in understanding the molecular biology of prion propagation, it is clearly not a specific disease marker.
In 1995 there was considerable concern in the United Kingdom about two very unusual, apparently sporadic cases of Creutzfeldt-Jakob disease in teenagers. (7,8) At the time only four cases of sporadic Creutzfeldt-Jakob disease had been recorded worldwide in teenagers, and none were in the United Kingdom. Most sporadic cases occur in persons 45 to 75 years of age. By March 1996, the United Kingdom Creutzfeldt-Jakob Disease Surveillance Unit had identified eight more young people with the disease. (9) They shared a unique clinicopathologic picture consisting of behavioral and psychiatric disturbances and early cerebellar ataxia, a prolonged duration of illness, and atypical electroencephalographic findings. (9) The clinical presentation was somewhat similar to that of kuru. The neuropathological changes were particularly striking, with extensive plaque formation and an unusual pattern of prion-protein immunostaining. It seems unlikely that such patients would not have been recognized in recent years. The probability that these young patients had sporadic Creutzfeldt-Jakob disease, with coincidental clustering over this short time frame, is vanishingly small. Until shown otherwise, we must assume that there is a new risk factor for Creutzfeldt-Jakob disease. Since these cases were seen only in the United Kingdom (despite intensive surveillance in other European countries with the same criteria and methods), where a novel bovine prion disease has affected over 160,000 cattle, it was natural to consider whether exposure to bovine spongiform encephalopathy, presumably before the ban on the use of bovine offal (which contained virtually all the infectious material) in 1989, was the explanation. To date, two more patients have been identified in the United Kingdom, with neuropathological confirmation. (10) A case has also been reported in France. (11) It is far too early to predict how many more cases will be identified. Nonetheless, early diagnostic markers for Creutzfeldt-Jakob disease are essential both to facilitate the differential diagnosis and, potentially, to screen blood and organ donors.
In this issue of the Journal, Hsich et al. (12) describe a new cerebrospinal fluid marker for these diseases. This is a welcome step forward. In 1986 Harrington and colleagues identified two proteins (designated 130 and 131) on two-dimensional gel electrophoresis, which provided a sensitive and specific marker for the diagnosis of Creutzfeldt-Jakob disease. (13) Unfortunately, this test was ill suited to routine diagnostic use. In the current report, these markers are identified as 14-3-3 proteins, and a positive immunoassay for these proteins in cerebrospinal fluid strongly supported a diagnosis of Creutzfeldt-Jakob disease in patients with dementia.
The authors screened a wide range of patients with neurologic diseases and found notable false positive results, anticipated from previous studies, in patients such as those with acute viral encephalitis and those who had had a stroke within one month before testing. This is not a screening test for patients without clinical dementia. In patients with dementia, the test appears to be highly specific and sensitive, but further analysis of larger numbers of patients with neurodegenerative diseases will be needed for us to be confident in this regard. In addition, it will be important to investigate how early in the disease this test is positive. Most cases of advanced Creutzfeldt-Jakob disease present little diagnostic difficulty. The usefulness of this test for patients with the recently recognized variant of Creutzfeldt-Jakob disease should also be evaluated.
An important consideration is the stability of 14-3-3 proteins in the cerebrospinal fluid. Since this test is likely to be available in only a limited number of centers, prolonged transport of some specimens will be required. Although it is interesting to speculate whether 14-3-3 proteins have a role in the disease process, the dramatic neuronal damage in Creutzfeldt-Jakob disease and other diseases in which positive results are found suggests, as Hsich et al. point out, that 14-3-3 proteins may simply be markers of neuronal injury.
All the prion diseases are associated with the accumulation in affected brains of an abnormal, partially protease-resistant isoform of the normal cellular glycoprotein, prion protein. The transmissible agent, or prion, appears to consist principally or entirely of this abnormal isoform, designated PrPSc, which derives from its cellular precursor, PrPC, by a post-translational modification that is thought to involve a conformational change. (14) A current model (15) of prion propagation is that PrPSc acts as a template that promotes the conversion of PrPC to PrPSc; this process occurs most efficiently when the interacting proteins share the same primary structure. Much of the barrier limiting the transmission of prions between different mammals is determined by differences in the amino acid sequences of prion protein between species. (15,16,17) This model of prion propagation can also explain why people who are heterozygous for the polymorphism at codon 129 are at lower risk for prion disease. (5) In inherited prion diseases, mutant PrPC spontaneously changes to PrPSc, and this is assumed to trigger the conversion of more PrPC. The etiology of sporadic Creutzfeldt-Jakob disease is unknown but may involve somatic mutation of the prion-protein gene or spontaneous conversion of PrPC to PrPSc as a rare, chance event. Although PrPSc-induced toxicity may cause neuronal damage, the demonstration of neurophysiologic abnormalities in prion-protein knockout mice that are similar to those seen in mice with experimentally induced scrapie and in humans with Creutzfeldt-Jakob disease suggests that loss of the normal cellular function of prion protein may play a part. (18)
Although detection of protease-resistant prion protein on immunoblotting can be used to diagnose prion disease, analysis of central nervous system tissue is usually required. More sensitive immunoassays able to detect PrPSc might allow detection of this protein in lymph nodes, other lymphoreticular tissues, and conceivably, lymphocytes in venous blood. The identification of an antiserum that will distinguish PrPSc from PrPC, without using its resistance to proteolysis, remains elusive.
How can we assess the risks to humans posed by bovine spongiform encephalopathy? Genetic susceptibility is likely to be important, and persons homozygous for codon 129 would be expected to be at higher risk than heterozygotes. The species barrier limiting the transmission of prions between cattle and humans cannot be studied directly, since this would require the inoculation of humans with bovine spongiform encephalopathy. The principal determinants of the barrier are the degree of homology between prion-protein molecules in the host and in the inoculum (15) and the strain of the agent; however, bovine spongiform encephalopathy appears to be caused by a single strain. (19) Transgenic mice expressing human prion protein, which can produce human PrPSc and human prions when challenged with an inoculum from a patient with Creutzfeldt-Jakob disease, are now being used to determine whether bovine prions can induce the production of human PrPSc. So far the results of such studies are reassuring. Incubation periods for bovine spongiform encephalopathy were unaltered in mice expressing human prion protein in addition to mouse prion protein, and only mouse PrPSc was detectable. (16) A more revealing experiment is the inoculation of mice expressing only human prion protein with bovine spongiform encephalopathy. (16) So far, such mice remain well up to 500 days after inoculation (mice of this genotype die of Creutzfeldt-Jakob disease in about 200 days). However, the results of studies of any animal model of human disease must be interpreted with caution, and it is important to appreciate that even a highly effective species barrier would not exclude transmission in some cases, given the extremely large numbers of people potentially exposed.
Transgenic mice, to which human prions can be easily transmitted, may be useful for strain-typing studies to determine the source of the infection in people. Bovine spongiform encephalopathy produces a distinct pathological "signature" in mice, even when previously passaged in other species. (19) This signature could be used to identify patients with bovine spongiform encephalopathy, should they exist.
References 1. Collinge J, Harding AE, Owen F, et al. Diagnosis of Gerstmann-Straussler syndrome in familial dementia with prion protein gene analysis. Lancet 1989;2:15-7. 2. Collinge J, Poulter M, Davis MB, et al. Presymptomatic detection or exclusion of prion protein gene defects in families with inherited prion diseases. Am J Hum Genet 1991;49:1351-4. 3. Collinge J, Brown J, Hardy J, et al. Inherited prion disease with 144 base pair gene insertion. II. Clinical and pathological features. Brain 1992;115:687-710. 4. Medori R, Tritschler H-J, LeBlanc A, et al. Fatal familial insomnia, a prion disease with a mutation at codon 178 of the prion protein gene. N Engl J Med 1992;326:444-9. 5. Palmer MS, Dryden AJ, Hughes JT, Collinge J. Homozygous prion protein genotype predisposes to sporadic Creutzfeldt-Jakob disease. Nature 1991;352:340-2. [Erratum, Nature 1991;352:547.] 6. Collinge J, Palmer MS, Dryden AJ. Genetic predisposition to iatrogenic Creutzfeldt-Jakob disease. Lancet 1991;337:1441-2. 7. Bateman D, Hilton D, Love S, Zeidler M, Beck J, Collinge J. Sporadic Creutzfeldt-Jakob disease in a 18-year-old in the UK. Lancet 1995;346:1155-6. 8. Britton TC, al-Sarraj S, Shaw C, Campbell T, Collinge J. Sporadic Creutzfeldt-Jakob disease in a 16-year-old in the UK. Lancet 1995;346:1155. 9. Will RG, Ironside JW, Zeidler M, et al. A new variant of Creutzfeldt-Jakob disease in the UK. Lancet 1996;347:921-5. 10. Chief Medical Officer's Report. London: Department of Health, July 1996. 11. Chazot G, Broussolle E, Lapras CI, Blattler T, Aguzzi A, Kopp N. New variant of Creutzfeldt-Jakob disease in a 26-year-old French man. Lancet 1996;347:1181. 12. Hsich G, Kenney K, Gibbs CJ Jr, Lee KH, Harrington MG. The 14-3-3 brain protein in cerebrospinal fluid as a marker for trans missible spongiform encephalopathies. N Engl J Med 1996;335:924- 30. 13. Harrington MG, Merril CR, Asher DM, Gajdusek DC. Abnormal proteins in the cerebrospinal fluid of patients with Creutzfeldt-Jakob disease. N Engl J Med 1986;315:279-83. 14. Pan KM, Baldwin M, Nguyen J, et al. Conversion of (alpha)-helices into (beta)-sheets features in the formation of the scrapie prion proteins. Proc Natl Acad Sci U S A 1993;90:10962-6. 15. Prusiner SB, Scott M, Foster D, et al. Transgenetic studies implicate interactions between homologous PrP isoforms in scrapie prion replication. Cell 1990;63:673-86. 16. Collinge J, Palmer MS, Sidle KC, et al. Unaltered susceptibility to BSE in transgenic mice expressing human prion protein. Nature 1995;378:779-83. 17. Telling GC, Scott M, Mastrianni J, et al. Prion propagation in mice expressing human and chimeric PrP transgenes implicates the interaction of cellular PrP with another protein. Cell 1995;83:79-90. 18. Collinge J, Whittington MA, Sidle KC, et al. Prion protein is necessary for normal synaptic function. Nature 1994;370:295-7. 19. Bruce M, Chree A, McConnell I, Foster J, Pearson G, Fraser H. Transmission of bovine spongiform encephalopathy and scrapie to mice: strain variation and the species barrier. Philos Trans R Soc Lond [Biol] 1994;343:405-11.
A new test of spinal fluid can detect Creutzfeldt-Jakob disease, a fatal, transmissible disorder of the human nervous system, scientists from the National Institutes of Health and the California Institute of Technology are reporting Thursday.
The test has also found related diseases in experimental animals, and is being studied to determine whether it can indicate "mad-cow disease," which has led to the slaughter of more than 170,000 cattle in England.
Previously, the only way to confirm the diagnosis of either Creutzfeldt-Jakob disease or the cattle disease was to obtain a tissue sample by brain surgery or to wait for the person or animal to die and conduct an autopsy. Both diseases cause dementia, and because there are no treatments, death usually occurs just months after symptoms appear.
"This is an important step forward," said Dr. Larry Schonberger, a medical epidemiologist at the Centers for Disease Control and Prevention, in Atlanta. "We've been hungry for a test for this disease. A lot of people have dementia, and it's unclear as to what it might be, and we're very hesitant to do a brain biopsy. This would be a much easier way to make a diagnosis while the patient is still alive."
"We think this is a terrific test," said Dr. Audrey Penn, deputy director of the National Institute of Neurological Disorders and Stroke. "It's important because it's the first step toward a commercially available test." Dr. Penn said she expected that some private company would develop and market the test.
The new test will be most useful for diagnosing Creutzfeldt-Jakob disease when symptoms have already led doctors to suspect that illness, said Dr. Michael Harrington, a developer of the test and co-author of the paper describing it in Thursday's New England Journal of Medicine. It will be especially helpful to doctors in distinguishing Creutzfeldt-Jakob from Alzheimer's disease, he said.
In his study, the test correctly identified 96 percent of patients with Creutzfeldt-Jakob disease, and correctly ruled it out in 96 percent of those who had other types of dementia. The test requires the performance of a spinal tap to obtain the spinal fluid, but the laboratory work is relatively easy to perform, he said, and could be handled by many laboratories.
Creutzfeldt-Jakob and mad-cow disease cause similar types of brain damage, and an epidemic among cattle in England, coupled with reports last year of an increase in Creutzfeldt-Jakob disease in people there, have led to fears that humans might contract the disease from eating infected meat.
Doctors are particularly concerned about a new variant of Creutzfeldt-Jakob disease that has stricken about a dozen young people in England, leading the European Union to ban the export of British beef.
No link between the cow disease and the human one has been proved, but the animal disease can cross species, and mad-cow disease is thought to have started in sheep and spread to cattle given feed that included sheep parts.
Hoping to control the livestock epidemic and regain its place in the world market, the British government has considered destroying as many 4.5 million cattle during the next five to six years.
No increase in Creutzfeldt-Jakob disease has been reported in the United States, where the disease reflects the worldwide rate and strikes one person in a million, resulting in about 250 cases a year, Schonberger said. The cow disease has not been detected in American cattle, he said.
Harrington a research scientist at the California Institute of Technology in Pasadena, developed the test with colleagues there and at the National Institute of Neurological Disorders and Stroke, cautioned that the new test cannot be used to screen apparently healthy livestock for mad-cow disease, or bovine spongiform encephalopathy.
The test cannot be used for screening, Harrington said, because it detects the disease only after symptoms have begun. During the long incubation between exposure to the disease-causing agent and the onset of illness, animals would test negative but later fall ill, and might pose a threat to human consumption or to other livestock.
Scientists have debated for more than a decade about the cause of Creutzfeldt-Jakob disease. It and the cow disease, along with the human disorder kuru, and scrapie in sheep, belong to a group of disorders known as transmissible spongiform encephalopathies, a name that refers to the sponge-like holes that they create in the brain.
Many scientists believe that the diseases are caused by prions, infectious proteins thought to cause brain damage. Other scientists suspect viruses or other microorganisms.
The new test does not identify the agent, but rather works by detecting a substance in spinal fluid, 14-3-3 protein, which is thought to leak from brain cells damaged by Creutzfeldt-Jakob or mad-cow disease.
In suspected cases of Creutzfeldt-Jakob disease, the new test is valuable because it allows diagnosis without subjecting the patient to brain surgery. That could also protect medical workers, Harrington said, by allowing them to avoid exposure to potentially infective brain tissue during surgery or autopsies.
He cited the case of an American neurosurgeon who died of Creutzfeldt-Jakob disease after accidentally jabbing himself with an instrument that had touched the brain of a patient with the disease. Spinal fluid is much less infective than brain tissue, Harrington said.
He also said that by helping to identify cases of Creutzfeldt-Jakob disease, the test might save transplant recipients from exposure to the disease, which has been transmitted in the past by corneas and other tissue taken from people not known to have had the disease.
The test may be particularly helpful to veterinarians in the United Kingdom, Harrington said, because mad-cow disease can be hard to diagnose. About a third of suspected cases turn out to be negative upon autopsy.
By identifying animals that really are infected, Harrington said, the new test might help workers and veterinarians avoid exposure to infected brain tissue, which may be dangerous to humans, though the risk is not known. Special precautions could also be taken in slaughtering and disposing of animals known to be infected.
Harrington said that because the initial tests were conducted on 257 people and 124 animals, further research was necessary to assure the accuracy and reliability of the test.
BOSTON -- Scientists have developed the first simple test for mad cow disease and its human equivalent, providing a possible new way of slowing the spread of this insidious killer. Until now, the only way to diagnose these incurable, mind-robbing illnesses with certainty was to look at a sample of brain tissue, something doctors are understandably reluctant to do before the death of the victim.
The inexpensive new test should allowve cattle, sparing the needless slaughter of animals that look sick but are actually healthy.
And it should enable doctors to distinguish patients with the exceedingly rare human variety of the illness Creutzfeldt-Jakob disease from those with much more common Alzheimer's, which has some of the same symptoms.
``The single most difficult diagnosis is assuring yourself whether the patient has Alzheimer's disease or Creutzfeldt-Jakob disease,'' said one of the developers of the test, Dr. Clarence J. Gibbs Jr. of the National Institutes of Health. ``If the patient has Creutzfeldt-Jakob disease, you have to advise the family that the patient will die within a year. If it's Alzheimer's, you tell them it will be a long, drawn-out affair.''
The new test doesn't offer any way to treat the disease. Practically any medical lab could offer the test now, using currently available equipment. The test was created by researchers from NIH and the California Institute of Technology. A report on the discovery was published in Thursday's issue of the New England Journal of Medicine. The human and cattle varieties of the disease emerged from obscurity earlier this year in Britain. An outbreak of bovine spongiform encephalopathy dubbed mad cow disease led to a European ban on British beef imports and the slaughter of nearly 200,000 cows.
Even more worrisome were suspicions, still unproven, that beef eaters could catch the cow disease. Some experts think that bad beef might be responsible for a recent cluster of Creutzfeldt-Jakob disease in 12 unusually young British victims.
Unlike Alzheimer's disease and similar illnesses, Creutzfeldt-Jakob can be spread through transplants of corneas and brain tissue. Dr. Michael G. Harrington of Cal Tech, another developer, said checking some organ donors with the new test could help reduce the risk of this sort of spread.
The test requires a spinal tap, a generally safe but unpleasant procedure. The samples of spinal fluid are then checked for a telltale protein. Even simpler versions, including ones that could be done on a farm or in a doctor's office, are in the works.
Creutzfeldt-Jakob disease strikes about one in 1 million people annually in the United States. Alzheimer's afflicts 30 percent of Americans by age 85.
Creutzfeldt-Jakob disease may lie dormant for years. But once symptoms appear, it quickly destroys the brain. Victims become demented and lose their coordination, sight and ability to speak.
In their study, the researchers tested spinal fluid from 71 people with Creutzfeldt-Jakob disease and 94 with other forms of dementia. It was about 95 percent accurate in telling them apart.
In an editorial in the journal, Dr. John Collinge of the Imperial College School of Medicine in London called the test ``a welcome step forward.''
However, the developers acknowledged drawbacks. The test reveals the disease only about the time symptoms start to appear, but apparently not during the long dormant stage. And it can produce erroneously positive results in people who have recently suffered strokes or who have encephalitis caused by the herpes simplex virus.
Dr. Frank O. Bastian of the University of South Alabama, an expert in the disease, predicted these shortcomings will limit its practical use.
``It's premature to make a lot of hullabaloo about this test,'' he said.
The test reveals a protein, called 14-3-3, that appears in unusually high levels in the spinal fluid of people with Creutzfeldt-Jakob disease, cows with mad cow disease or other animals with similar illnesses. It probably results from the destruction of nerve cells, which explains why it also shows up soon after a stroke.
Creutzfeldt-Jakob disease and related ills are thought to result at least in part from rogue proteins called prions. These are mutant versions of proteins that occur normally in the body.
The Genetics Institute said Wednesday that it had developed a library of several thousand genes and their related proteins that could be scanned for potential new drugs.
The instructions that prompt a cell to produce a specific protein are encoded in a gene, a double strand of DNA that resides in the nucleus. There are 100,000 genes in the human body, which constitute the human genome, but not all are of therapeutic interest.
The Genetics Institute's breakthrough lies in creating a novel mechanism to screen out only those genes that encode secreted proteins, meaning proteins that leave the cell and are therefore more likely to play a therapeutic role. To date, this technology, for which Genetics Institute has received a patent, has identified 5,000 secreted genes from a wide variety of tissue sources. Genetics Institute's scientists have produced a biochemical "library" of 250 proteins using this information.
This so-called "functional genomics" is in contrast to the approach taken by most genomics companies, which is primarily a combination of generating as many gene sequences or portions of sequences as possible and scanning vast amounts of hereditary data to identify all the genes implicated in a given disease like cancer or diabetes.