A study by US researchers has shown that a woman from Colombia with high levels of early-onset Alzheimer's-related pathology did not present with any disease symptoms until much later in life. The research suggests that the presence of a rare mutation of the APOE gene (a gene associated with Alzheimer's disease) may have acted as a protective factor to disease development.
'This single case opens a new door for treatments of Alzheimer's disease, based more on the resistance to Alzheimer's pathology rather than on the cause of the disease,' said co-author Dr Yakeel Quiroz, a researcher at Massachusetts General Hospital.
The study, published in Nature Medicine and led by Massachusetts General Hospital (MGH) in collaboration with the University of Antioquia, Schepens Eye Research Institute of Massachusetts Eye and Ear, and Banner Alzheimer's Institute, investigated the potential protective effects of a genetic-mutation in those with early-onset Alzheimer's disease.
Researchers studying 1200 individuals genetically predisposed to the disease identified one woman who showed no disease symptoms, despite having both a high degree of brain amyloid – the hallmark of Alzheimer's – and the presence of a mutation in the Presenilin 1 (PSEN1) known to cause early-onset dementia. Unlike similarly predisposed family members who presented with symptoms in their forties, the unnamed woman only began to show signs of mild cognitive impairment in her seventies.
The researchers subsequently tested her genome and identified a rare variant of the Alzheimer's-associated APOE gene they named 'Christchurch'. They hypothesise that it counteracts the detrimental effects of the PSEN1 mutation, preventing the spread of the protein, tau, which forms 'tangles' inside neurones in the brains of people with Alzheimer's, disrupting their function.
Although inherited Alzheimer's is rare, understanding the role of protective genetic factors could help transform development of new treatments. 'It will be critical to support these results with more evidence', said Dr Sara Imarisio, of Alzheimer's Research UK, who was not involved in the study, 'but this case-study provides a promising new direction for future research'.
Dr Michael Greicius, an expert in Alzheimer's genetics from Stanford University, emphasised that the patient's combination of genes is 'exceedingly uncommon and possibly unique'.
Dr Eric M Reiman, executive director of Banner Alzheimer's Institute and co-senior author of the study, that 'this study underscores the importance of APOE in the development, treatment, and prevention of Alzheimer's, not to mention the profound impact that even one research volunteer can have in the fight against this terrible disease'.