The hypomyelinating leukodystrophy associated with variants in both FAM126A and PI4KA described here, may likely relate to the role of PI4P or its further phosphorylated derivatives, which together with myelin basic protein is required for myelin sheath growth.14,26-29 Interestingly, PI4KIIIα has been recently shown to play a pivotal role in myelination of the peripheral nervous system.29 Here, MBP is linked to leukodystrophy.