Within the GCKs, the GCKIII subfamily of kinases includes the mammalian kinases MST3, MST4, and YSK1/SOK1/STK25 [3], which have been implicated in processes such as apoptosis [6] and axon outgrowth [7], and may be involved in diseases such as Alzheimer's [8], type 2 diabetes [9], Parkinson's disease [10], and cerebral cavernous malformations [4]. Here, STK25 is linked to Parkinson disease.