Formally defined as a decline in cognitive abilities and memory sometimes accompanied by degradation of language, emotional expression and motivation. At present, it is believed that between 50 and 70 percent of cases of dementia are some variant of Alzheimer Syndrome. Other common causes are

  1. vascular dementia  – usually a series of mini-strokes
  2. Lewy body dementia – usually linked with Parkinson’s disease and characterized by the presence of Lewy bodies which are clumps alpha-synuclein and ubiquitin proteins
  3. frontotemporal dementia – the characteristic is significant loss of spindle neurons in the frontal lobe
  4. Creutzfeldt-Jakob disease – prions are incorrectly-shaped proteins that distort other proteins and damage the local area. Sometimes known as ‘mad cow’ disease

Universally, prospects are bleak.

After cruising the human genome databases there are well over 100 dementias thought to be genetically linked. One problem that has escaped explanation is why one does not get Alzheimer (or most other syndromes) symptoms immediately (at birth) as opposed to 60 years later.

So far, three genes are implicated in early onset Alzheimer Syndrome and 22 are involved in classical late onset Alzheimer.

One gene of interest is on chromosome 21 at location q21.3 (molecular location between base pairs 25,880,550 and 26,171,128). Known to intimates as APP (short for amyloid precursor protein), this gene is being closely studied. One conjecture is that a defective copy leads to Alzheimer Syndrome, but two defective copies causes earlier and more severe Alzheimer Syndrome. For most cases of chromosome 21 trisomy (Down Syndrome) there could potentially be THREE defective copies of the gene. Among all the other damage caused by Down Syndrome there’s usually a fair chance of having dementia 20 or 30 years earlier than the general population. As far as I know, APP is the only gene thought of known to  act quite this way.

For now, the medical consensus seems to be make sure you have enough B12, do not smoke, and try to avoid oxygen deprivation (so go easy on astronautics, deep sea diving, cave exploration, mountain climbing and so on).

Of concern is

  1. the list of genes involved is almost certainly going to grow
  2. people get Alzheimer symptoms without having defects in any of the known genes
  3. people with damaged genes do not get Alzheimer symptoms

Concerns 2 and 3 should not be an excuse not to get your DNA analyzed. Just take the results with a grain of salt.