Mutations in AARS2 (alanyl-transfer (t)RNA synthetase 2) are emerging as a rare cause of leukodystrophy with similar clinical, imaging and radiological phenotype to CSF1R mutations.28 29 This is an autosomal recessive disorder, but frequently appears sporadic, with a younger age of onset than CSF1R (mean age 29 years, range 15–44 years). Here, CSF1R is linked to leukodystrophy.