A ROUTINE diagnostic test for Alzheimer鈥檚 disease has been licensed for use
by doctors. Innogenetics, a biotechnology firm in Ghent, Belgium, says its test
picks up early signs, which should allow treatment once new drugs for the
disease become available.
Early Alzheimer鈥檚 can be difficult to distinguish from other mental problems
of old age, caused by stroke, for example, or neurodegenerative diseases. The
new test relies on an antibody that recognises tau, a protein involved in
intracellular transport. In Alzheimer鈥檚 patients, tau is covered with too many
phosphate groups, forming tangled fibrils in the brain that may contribute to
dementia. Looking at these microscopic brain structures after death is currently
the only way to confirm an Alzheiner鈥檚 diagnosis with certainty, although some
memory tests can hint at the disease
(This Week, 2 August 1997, p 6).
Levels of tau increase in the cerebrospinal fluid (CSF) very early in the
disease, says Eugeen Van Mechelen of Innogenetics. CSF is easy to get at by
using a needle to draw it off from the spine. Alzheimer鈥檚 tests based on other
proteins in CSF have been available to researchers for several years, but
Innogenetics is the first to register a test for routine diagnosis.
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Michel Goedert of the MRC Laboratory of Molecular Biology in Cambridge
cautions that other conditions, such as stroke, can also raise levels of tau.
But Van Mechelen argues that these conditions have different symptoms. 鈥淐linical
symptoms must always be considered along with the test,鈥� he says. Five per cent
of Alzheimer鈥檚 patients show normal levels of tau, but Innogenetics is
developing a supplementary test for beta-amyloid protein, since people with
Alzheimer鈥檚 often have lower levels of this in their CSF.