Neuronal branches in SETD1A deficient mice are shorter and stunted. Switching off another gene, LSD1, nullifies the harmful effects of SETD1A on neuron and axon growth. After inhibiting LSD1, SETD1A deficient mice showed improved memory and axon growth. Inhibiting LSD1 not only acted on memory deficits linked to schizophrenia but also acted on the underlying molecular mechanisms associated with axonal growth.