Saturday, March 7, 2020

Where are we with Alzheimer's Disease? Of Mice and Men

Two recent items prompted this post. My sister, who works at McGill University in Montreal, Canada, sent me a news item trumpeting that McGill researchers had discovered a cure for Alzheimer’s disease (AD) using a special formulation of lithium. Another said that researchers at the University of California at San Francisco had discovered a simple blood test to diagnose the disease. Great! A simple test and a cure? What more could we ask? Yet at the same time, the US Public Health Service (USPHS) task force on prevention recently came out saying there was no basis to recommend screening patients for dementia. Who is right? What is the true state of affairs?

Alzheimer’s is the leading cause of dementia world-wide, and it gets more common as we age. Almost 6 million Americans are living with Alzheimer’s in 2020, 97% of whom are over 65. The incidence is 3% in those 65-74, 17% in people 75-84 and 32% in those 85 and older. We know that many factors influence whether one gets dementia, including age and genetics. One way to prevent it is to die young, but I do not recommend this. Another is to choose different parents; not a practical idea. Dementia is not inevitable with age. Dutch investigators recently reported on a group of cententarians who remained cognitively intact well beyond age 100.

Risk factors that we can control include making sure we exercise regularly and that we control our cardiovascular risk factors: diabetes, obesity, smoking and high blood pressure. What about vitamins? Careful analysis of many studies has found little or no evidence that any of the popular supplements (B vitamins, antioxidants, etc.) have any beneficial effect.

How is Alzheimer’s diagnosed? Traditionally, it has been a clinical diagnosis with no easy X-ray or blood test to confirm the diagnosis. Certain genetic markers, known as APOE genotypes, increase the likelihood but do not make a diagnosis. Certain abnormal proteins accumulate in the brain in patients with Alzheimer’s, and these can be measured in the spinal fluid, but this requires an invasive spinal tap for samples. They can also be imaged with a PET scan using special markers. Neither of these are practical for testing millions of people. The study reported by the UC-SF neurologists suggested that levels of a protein called pTau81 in the blood were much higher in Alzheimer’s patients than in healthy people of the same age. If this early research proves to be accurate, it will be a definite improvement in our ability to make a diagnosis with more confidence.

Diagnosis of a condition is the first step. While necessary to proceed, diagnosis is not the endpoint, which is treatment. There is the rub. All the medicines now available to treat AD are minor holding actions: they slow down the progression of the disease but are far from a cure. Many putative “breakthroughs” in treating Alzheimer’s have come to a dead end, with no benefit or even harm. This made the news out of McGill so potentially exciting. When I was able to find the paper reporting the study, it was a study conducted in genetically modified mice. Even if these results are repeated in other labs, it is a long way from changing the chemistry of a mouse brain to curing humans with Alzheimer’s.

It seems the USPHS was right. If we have nothing in the way of a cure or even a major help to offer sufferers with AD, mass screening is not a high priority.

So, exercise regularly, keep your weight down, be socially engaged, treat your cardiovascular risk factors and hope that what works in mice may someday be shown to work in men (and women).

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