Until recently, the role of astrocytes, glial cells that normally support motor neurons, in motor neuron death has been a mystery, but new research sheds light on molecular mechanisms responsible for motor neuron death in ALS. In this study, scientists demonstrated the explicit loss of major histocompatibility complex I (MHCI) expression in the outer membrane of motor neurons in ALS, leading to motor neuron vulnerability to ALS astrocyte toxicity.