In humans, brain epigenetic age estimated using the recently developed “Cortical clock” was inversely correlated with decreased neuronal cell proportions estimated from genome-wide DNAm data (Shireby et al., 2020), but this did not affect its association with neurodegenerative diseases such as Parkinson’s and Alzheimer’s diseases (Grodstein et al., 2021). The gene discussed is CLOCK; the disease is early-onset autosomal dominant Alzheimer disease.