HDAC4 and hypersomnia: Two very recent studies suggest that the phosphorylation of HDAC4 and possibly HDAC5 by SIK3 regulates the levels of NREM sleep (89, 90), as heterozygous Hdac4S245A mice, in which the SIK3 target is mutated, show reduced NREM time, and overexpression of HDAC4(S245A) using the adeno-associated virus AAV-PHP.eB in Sik3 (Sleepy) mice rescued the hypersomnia phenotype (89).