RTL8A and Prader-Willi syndrome: Here, we demonstrate that Rtl8a and Rtl8b play important roles in the brain: their double knockout (DKO) mice not only exhibit reduced social responses and increased apathy-like behaviour, but also become obese from young adulthood, similar to patients with late Prader–Willi syndrome (PWS), a neurodevelopmental genomic imprinting disorder.