RNA Antibody

[Guest guest]

Anti U1-RNA Antibody

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Rheumatic diseases can be difficult to diagnose. It's also hard to predict when

they will become more or less active. A new lab test assists in the diagnosis

and treatment of mixed connective tissue disease (MCTD), one of the

multi-systemic rheumatic diseases.

The test looks for an antibody called anti-U1 RNA. Researchers at the University

of Missouri-Columbia have found that the level of this antibody in a patient's

blood corresponds to the severity of her disease. It's only the second antibody

known to show this kind of relationship. The other one, anti-DNA, is a marker

for lupus.

Antibodies are proteins produced by the blood. Antibodies usually fight off

foreign proteins, called antigens, that exist on viruses and bacteria. In

autoimmune diseases like MCTD, lupus, and some forms of arthritis, the

antibodies react with the body's own tissues.

While studying anti-U1 RNA antibody, doctors at the University of Missouri

observed a woman in her 30s with MCTD. Her disease was in remission; she was

working and feeling fine. The doctors thought she could be used as a control, a

standard of comparison, in their search for the antibody in patients with active

MCTD. Much to the researchers' surprise, the woman's anti-U1 RNA antibody count

was very high.

" There must be something wrong with our test, " one of the researchers, Dr.

Gordon Sharp, recalls thinking.

The next week, however, the woman experienced chest pain and muscle weakness, a

relapse of her MCTD. The increase in her anti-U1 RNA antibody level had been a

warning sign. Her medication was subsequently increased and her disease went

into remission again.

Now Sharp and his colleagues are monitoring the levels of anti-U1 RNA antibodies

in all their patients with MCTD. An increase in the antibody level signals them

to re-evaluate the patient and consider adjusting the dosage of the medication,

usually a corticosteroid, to prevent flare-ups of the disease.

Discovering the antibody

The anti-U1 RNA antibody was discovered in 1983 by Deutscher, PhD, a

biochemist, and her colleagues at Duke University. They took the sera from two

patients with connective tissue disease and found that their antibodies attached

to a type of ribonucleic acid (RNA), the cell material that helps decode genetic

instructions held in DNA. Most antibodies bind proteins, so they knew they had

something unusual. They later identified the type of RNA as U1-RNA, named for

its abundance of a compound called uracil.

When Deutscher joined the Biochemistry Department at the University of

Missouri-Columbia, she found physicians with a strong interest in connective

tissue diseases and access to their large population of patients. She has

collaborated with Dr. Hoffman, an immunogeneticist and Dr. Sharp, the

rheumatologist who heads the MARRTC.

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The ANA lab

The anti-U1 RNA antibody is the most recent addition to the autoantibody profile

offered by the ANA (Antinuclear Antibody) laboratory at the University of

Missouri. The lab analyzes over 6,000 blood samples a year from patients with

various autoimmune diseases.

" The antigen is our tool, " said lab supervisor Grace Wang.

The lab tests for anti-U1 RNA by adding a radioactively-labelled antigen to a

patient's serum sample. The antibody in the serum combines with the antigen,

making it precipitate, or fall out of the solution. The amount of radioactivity

in the precipitate then tells how much anti-U1 RNA antibody is present.

The University of Missouri ANA lab, begun about 20 years ago, is one of the

oldest labs of its type and may be the only clinical pathology lab in the United

States offering the new anti-U1 RNA antibody test.

http://www.hsc.missouri.edu/~arthritis/u1rna.html