Different Types of Alzheimer’s Disease (based on Mayo Brain Bank)

A couple of years ago (September 2011), the Mayo Clinic published interesting research on the different types of Alzheimer’s Disease, based on neuropathologic findings.  Of course there’s the “typical” type of AD that most of us are familiar with.  There are two other types that are new to me —

  • hippocampal sparing (HpSp)
  • limbic predominant (LP)

One of Brain Support Network’s missions is to assist families around the United States with brain donation.  We have helped over 150 families donate a loved one’s brain.  We occasionally see these two non-typical AD diagnoses on neuropathology reports.  We look forward to more publications describing these two non-typical types of Alzheimer’s.

In this study, 889 cases of AD at the Mayo Clinic brain bank were examined.  Just over 11% of the cases were hippocampal sharing, and 14% of the cases were limbic predominant.  So these two non-typical AD types represent 25% of all AD cases.

Because the “hippocampal sparing (HpSp)” type had less hippocampal atrophy than typical AD, this meant that memories were relatively more preserved than with typical AD.  “Patients with hippocampal sparing AD were younger at death (mean 72 years) and a higher proportion of them were men (63%). … HpSp had a shorter disease duration. … A non-AD clinical diagnosis was more frequent (30%) in HpSp than LP and typical AD. Examples of non-AD clinical diagnoses included behavioral variant of frontotemporal dementia (12%) and other focal cortical syndromes (13%), such as progressive nonfluent aphasia, semantic dementia, posterior cortical syndrome, and corticobasal syndrome, as well as parkinsonian disorders (4%), such as progressive supranuclear palsy and Parkinson’s disease dementia.”

“[Those] with limbic-predominant AD were older (mean 86 years)and a higher proportion of them were women (69%).”  Disease duration was the same as with typical AD.  “LP most often had an antemortem clinical diagnosis of AD (94%). Of the 6% of LP who were given a non-AD clinical diagnosis, only a few were considered to have behavioral variant of frontotemporal dementia (n=2) or focal cortical syndromes (n=1), but they were comparable on parkinsonian diagnoses (n=4).”

“Neither initial, nor final MMSE scores assessed within three years of onset and death, respectively, were different among the AD types. When MMSE scores were evaluated with respect to disease duration, apparent differences were observed for HpSp. Figure 4 shows rapid progression of deterioration on MMSE in HpSp, with many patients progressing from normal to impaired values in a few years, declining at a rate of 5 points per year on the MMSE. On average, HpSp cases showed a steeper slope than both LP and typical AD.”

As for genetics, the researchers found:

“Microtubule-associated protein tau (MAPT) H1H1 genotype was more common in limbic-predominant AD (70%) than in hippocampal sparing AD (46%, but did not differ significantly between limbic-predominant and typical AD (59%). Apolipoprotein E (APOE) ɛ4 allele status differed between AD subtypes only when data were stratified by age at onset.”

The researchers argue that these distinct AD clinicopathological subtypes “should be considered when designing clinical, genetic, biomarker, and treatment studies in patients with AD.”

The full article is available online at no charge: