The FN1+ MG subcluster exhibits high expression of the Alzheimer’s disease risk genes ABI3, CD33, and PTK2B (52, 53), suggesting that this component of CSF microglia-like cells could emerge from a specific myeloid cell response to protein aggregates accumulating in the parenchyma during neurodegeneration. Here, CD33 is linked to early-onset autosomal dominant Alzheimer disease.