12.5 kda cystatin may generate first simple test for multiple sclerosis
Mar 6, 2006 - 4:53:37 PM
Johns Hopkins scientists report the discovery of a protein found only in cerebrospinal fluid that they say might be useful in identifying a subgroup of patients with multiple sclerosis (MS) or identifying those at risk for the debilitating autoimmune disorder.
MS strikes over 10,000 Americans each year, most of whom are women, and causes weakness, numbness, a loss of muscle coordination, and problems with vision, speech, and bladder control. It is a disorder in which the immune system destroys myelin, the covering of nerves that helps transmit signals. Cerebrospinal fluid (CSF) is the watery fluid that surrounds and cushions the brain and spinal cord.
The federally funded Hopkins research, reported in the February issue of the Annals of Neurology, is important, the researchers say, because unlike other autoimmune diseases in which the body attacks its own tissues, MS cannot be diagnosed with a simple blood or other test.
While it is recognized that there might be several forms of MS, laboratory-based tests need to be developed to diagnose these subtypes.
"There is the possibility now that the protein we identified, 12.5 kDa cystatin, can be used to diagnose MS, perhaps in its earliest stages, and also to monitor treatment by measuring its levels in CSF," says Avindra Nath, M.D., a professor in the Department of Neurology at The Johns Hopkins University School of Medicine and lead author of the study.
Working with human CSF, the Hopkins team showed that 12.5 kDa cystatin is a breakdown product of a larger protein called cystatin C or 13.4kDa, which in turn blocks activity of some enzymes, including cathepsin B. Cathepsin B has been linked to demyelination-the destruction of the nerve sheath. The term kDa refers to Kilodalton, the weight of one molecule of a substance.
"In fact, those patients who had more of the breakdown product of 12.5 kDa cystatin also seemed to have the highest cathepsin B inhibition," Nath said.
The investigators made their finding using a sophisticated technique called SELDI-time-of-flight mass spectroscopy that can find one specific protein in a complex mixture based on its weight. They used it to examine CSF samples from 29 patients with MS or pre-MS symptoms such as numbness on one side; 27 patients with transverse myelitis, a painful inflammation of spinal cord nerves; 50 infected with the AIDS virus (which can cause nerve damage); and 27 with other neurological diseases. The Hopkins scientists analyzed CSF instead of blood samples because CSF better represents local events in the brain than does blood, according to Nath. And the high concentrations of many proteins in the blood can mask proteins that might be biomarkers for MS, he added.
The team found that the 12.5kDa fragment of cystatin C occurred in CSF samples from two-thirds of patients with MS or the pre-MS conditions. Moreover, although total cystatin C levels in MS patients were not different from control patients without the disease, patients with MS had a larger proportion of the 12.5 kDa compared to 13.4 kDa cystatin C than did other patients. Thus, the presence of the 12.5 kDa fragment might identify a subgroup of MS patients.
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