Overall, the two studies support SNAP as a “generally non-AD heterogeneous diagnosis that does in fact exhibit greater cognitive decline with age, even if subtle in the Mormino study, with an increased risk of MCI and dementia. If we look at the neuropathology of AD cases, we find similar additional pathologies, so maybe SNAP is that minus the AD piece,” said Dr. Caselli, who was not involved in either study.
The heterogeneity explains “our difficulties understanding” the nature of SNAP, Sylvia Villeneuve, PhD, said in an editorial to the Harvard study (JAMA Neurol. 2016 Aug 22. doi:10.1001/jamaneurol.2016.2842).
“Given that the cognitive and brain profile of most SNAP individuals are stable over time, some authors have suggested that neurodegeneration should not be a defining feature of SNAP. … Part of what we capture as SNAP represents a tail of the normal aging distribution,” said Dr. Villeneuve of McGill University in Montreal. “A better comprehension of the biomarkers used to characterize SNAP will be important, with an awareness of the limitations of bimodal markers” – the yes/no answers used for NIA and SNAP classification – “especially those with cutoffs that do not have a biological basis.”
Both studies were funded at least in part by the National Institutes of Health. Dr. Gordon reported research work with Avid Radiopharmaceuticals; Dr. Mormino had no industry disclosures. Other investigators in both projects reported ties to several companies, including Eli Lilly, Janssen, AbbVie, Roche, and Pfizer. Dr. Villeneuve had no disclosures.