CDKL5 and early-onset autosomal dominant Alzheimer disease: The finding that treatment with P021 shows no advantages in normal animals is in line with the present evidence in Cdkl5 KO mice, and suggests that P021 treatment may help brain development/function under some abnormal brain conditions such as Alzheimer’s disease (AD) [52] and Down syndrome (DS) [42], but not in the case of CDKL5 deficiency.