SPP1 and motor neuron disorder: Several of these genes have been implicated in motor neuron function: Kcng445 and Kcnj1446 modulate firing properties of motor neurons, Scn4b mutant animals show motor defects47, Grin3b is a motor neuron-specific NMDA receptor subunit that forms excitatory glycinergic receptors48, expression levels of Aox1, Col5a3, and Gls2 are altered in mouse models of a motor neuron disease ALS49–51, and Spp1 shows reduced expression in motor neurons and increased levels in cerebrospinal fluid of ALS patients52–54.