In 1901, Aloysius Alzheimer started following the case of Auguste Deter, a 50 year old woman, who was showing signs of dementia despite her early age. After she died in 1906, he published his findings and introduced the world to Alzheimer's Disease. While his description of the disease has been refined over the years, he correctly identified it as a specific condition different than other neurological issues.
After her death, Alzheimer had Deter's brain brought to a lab where he prepared slide to study. The stains applied to the slices of her brain allowed him to see the plaque which we associate with this disease. The slides were were lost and were not found again until 1997.
Last week, research was published which confirms that August Deter had Alzheimer's. DNA was extracted from some of the brain samples preserved in the slides and analyzed. The results show a single genetic mutation caused her early on-set Alzheimer's.