Down syndrome and Alzheimer disease

Area of Science:

• Neuroscience
• Neuropathology
• Genetics

Background:

• Individuals with Down syndrome exhibit neuropathological changes resembling Alzheimer disease later in life.
• These changes include the formation of neurofibrillary tangles and beta/A4 amyloid protein deposits (senile plaques and amyloid angiopathy).
• The accumulation of these pathological hallmarks increases with age in Down syndrome individuals.

Purpose of the Study:

• To characterize the specific pattern of neurofibrillary tangle and senile plaque accumulation in the brains of individuals with Down syndrome.
• To examine the progression and vulnerability of specific neuronal populations to these Alzheimer-like pathologies.

Main Methods:

• Histopathological examination of brain tissue from individuals with Down syndrome across a wide age range (13-71 years).
• Detailed mapping and characterization of the distribution and density of neurofibrillary tangles and senile plaques.
• Analysis of specific neuronal vulnerability within the hippocampal formation and entorhinal cortex.

Main Results:

• A predictable pattern of neurofibrillary tangle and senile plaque deposition was identified in the hippocampal formation.
• Specific neuronal populations, including those in layer II of the entorhinal cortex and the CA1/subiculum field, were found to be highly vulnerable and affected early.
• The pathological changes evolve over 20-30 years from mild to severe stages.

Conclusions:

• Down syndrome brains exhibit a characteristic and predictable pattern of Alzheimer disease-like pathology.
• The genetic anomaly on chromosome 21, specifically the amyloid precursor protein gene, is hypothesized to contribute to amyloid accumulation.
• Further research is ongoing to validate the hypothesis linking chromosome 21 gene dosage to Alzheimer pathology in Down syndrome.