CHIT1 and early-onset autosomal dominant Alzheimer disease: Studies on frontotemporal dementia, ALS and Alzheimer’s disease suggest that CHIT1 reflects microglial activity and is associated with the rate of disease progression in ALS,9, 11, 12 while histopathological work in Alzheimer’s disease, and recently ALS, suggests that CHI3L1 is expressed preferentially by astrocytes14, 21 and studies in ALS suggest that CHI3L1 is more closely associated with clinical features of central dysfunction denoted by upper motor neuron involvement and degree of cognitive dysfunction.11, 12, 14