Given that H3Q5ser plays a vital role in neuronal differentiation and olfactory sensory processing and that PAD4-expressing neurons release citrullinated proteins in Alzheimer’s disease, the crosstalk between H3Q5ser and H3cit may also be relevant to nervous system functions and awaits future study (6, 35, 36). Here, PADI4 is linked to early-onset autosomal dominant Alzheimer disease.