Regarding the relationship between the phosphorylation at S551 and T221 in SIK3, the enhancement of the downstream transcription and the hypersomnia phenotype in Sik3Slp mice were abolished by the introduction of the T221A mutation into the Slp allele [8], suggesting that the gain-of-function effect of the Slp or S551A mutation depends on the T221 phosphorylation and the SIK3 kinase activity [8, 19]. The gene discussed is SIK3; the disease is hypersomnia.