Alzheimer's disease, long thought to be a single disease, actually consists of three distinct subtypes that may need to be treated differently, a new study has found.
The study also found that one of the three variations, the cortical subtype, appears to be fundamentally a different condition than the other two, said Dr Dale Bredesen, the study's author, a University of California - Los Angeles professor of neurology and member of the Easton Laboratory for Neurodegenerative Disease Research.
"Because the presentation varies from person to person, there has been suspicion for years that Alzheimer's represents more than one illness," said Bredesen.
"When laboratory tests go beyond the usual tests, we find these three distinct subtypes.
"The important implications of this are that the optimal treatment may be different for each group, there may be different causes, and, for future clinical trials, it may be helpful to study specific groups separately," he said.
The subtypes of Alzheimer's disease include: inflammatory, in which markers such as C-reactive protein and serum albumin to globulin ratios are increased; non-inflammatory, in which these markers are not increased but other metabolic abnormalities are present; and cortical, which affects relatively young individuals and appears more widely distributed across the brain than the other subtypes of Alzheimer's.
The cortical subtype typically does not seem to cause memory loss at first, but people with this subtype of the disease tend to lose language skills. It is often misdiagnosed, typically affects people who do not have an Alzheimer's-related gene and is associated with a significant zinc deficiency.
The findings of the two-year study, which involved metabolic testing of 50 people, appears in the journal Aging.
Bredesen and his team now seek to determine whether the subtypes have different underlying causes, and whether they respond differently to potential treatments.