AQP4 and myopathy: The NMO target protein AQP4 is expressed not only in the CNS but also in some peripheral organs, including the kidney, skeletal muscle, stomach, and airways (166); however, the peripheral organs are relatively spared, except for a few reports of myopathy (36), even though the AQP4-IgG titer is higher in the serum than in the CSF (167).