USP9X and neurodevelopmental disorder: The effect of Usp9x deletion on NPs on brain development was not as severe as inhibition of each pathway alone possibly reflecting the counteracting roles of Notch and Wnt in progenitor cells40 Nonetheless, missense mutations in USP9X and loss of heterozygosity give rise to multiple neurodevelopmental disorders in humans65, 66 and both USP9X gain of function and loss of function67 are tumorigenic in numerous cell types.