MATR3 and motor neuron disorder: Initially encompassing the inclusion body myopathy, Paget disease, frontotemporal dementia (IBMPFD) motor neuron disease spectrum, which includes VCP, HNRNPA2B1, and HNRNPA1 genes (MSP1, MSP2, and MSP3, respectively), MSP classification now incorporates the pathologies associated to SQSTM1 (MSP4), MATR3 (MSP5), TIA1, and eventually OPTN genes (28).