The Nun study: clinically silent AD, neuronal hypertrophy, and linguistic skills in early life.
Level 4 - case-series / case-control
Post-mortem case-control stereological study
PubMed 19587326 · doi:10.1212/WNL.0b013e3181b01077
What was done
Design-based stereology was used to measure the volumes of neuronal cell bodies, nuclei, and nucleoli in the CA1 region of the hippocampus in autopsied brains from the Nun Study. Four groups were compared: asymptomatic Alzheimer disease with pathology but normal cognition (ASYMAD, n = 10), mild cognitive impairment (MCI, n = 5), clinical Alzheimer disease (AD, n = 10), and age-matched controls (n = 13). Early-life linguistic ability was also assessed and compared across all groups.
What was found
In CA1 neurons, ASYMAD subjects demonstrated significant hypertrophy compared with MCI subjects in cell body volume (+44.9%), nuclear volume (+59.7%), and nucleolar volume (+80.2%). Similar significant differences in neuronal size were observed between ASYMAD and controls. Additionally, early-life idea density scores were significantly higher in the control and ASYMAD groups compared to the MCI and AD groups.
Why it matters
This study suggests that early-life cognitive reserve (reflected by linguistic ability) and hippocampal neuronal hypertrophy may serve as compensatory mechanisms that preserve cognitive function despite the accumulation of substantial Alzheimer pathology.
Limits
The total sample size was small (n = 38, including only 5 subjects in the MCI group), which reduces statistical power. The study was conducted in a highly specific, homogeneous cohort of Catholic nuns, limiting generalizability to broader populations. Post-mortem observational data cannot establish whether neuronal hypertrophy directly causes cognitive resilience or is a secondary marker.
Cited by
- supports In the Nun Study, participants maintained cognitive function and high cognitive capacity despite postmortem findings of significant Alzheimer's amyloid pathology.