nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
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Tuesday, August 10, 2010

A Test That Can Predict The Development Of Alzheimer's Disease

A spinal fluid test that's very accurate in identifying memory-loss patients early on.

There have been some recent significant advances in our understanding of Alzheimer's disease (AD).  One of these appeared in the Archives of Neurology (Aug 2010).  It's one of a series of sudies that identify "biomarkers" for a disease.

A biomarker is a compound, usually a protein, that is present only when the person has the disease, or is developing the disease.  Knowing how to measure such a biomarker will give physicians a head-start on diagnosing a problem before it become severe or ireemediable.

In Alzheimers there's more than one suspected marker.  These researchers looked at identifying a mix of markers, in this instance called "β-amyloid protein 1-42 + phosphorylated tau181P."  We see amyloid and tau in the brains of people with AD.  Now it can be measured in the cerebospinal fluid, as a signature for the development of AD.

The sensitivity of the test seems pretty striking, but there is a caution.  See if you can pick what that caution is from looking at the data:

For Onion Peelers,
The AD signature was found in 90%, 72%, and 36% of patients in the AD, mild cognitive impairment, and cognitively normal groups, respectively. The cognitively normal group with the AD signature was enriched in apolipoprotein E 4 allele carriers. In 1 study consisting of 68 autopsy-confirmed AD cases, 64 of 68 patients (94% sensitivity) were correctly classified with the AD feature. In another data set with patients (n = 57) with mild cognitive impairment followed up for 5 years, the model showed a sensitivity of 100% in patients progressing to AD.

These are pretty high percentages for a screening test.

But, notice that the signature was positive in 36% of cognitively normal people.  The authors think that means that the biomarker is present even before symptoms begin.  But that's true only if these normal persons all go on to AD.  And it's not clear that they followed the cognitively normal group to see if they developed Alzheimers.  We'll have to wait for further clarification.

If not, then over a third of normal people will have an abnormal test result that may be spurious. 

Even so, this looks like a real step forward in diagnosing a disease that affects so many, but can't be diagnosed until the disease is fully developed.

Doc D

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