Extended Data Fig. 10: Immunohistochemistry showing BCMA protein expression in brain tissue of the patient and in a control brain.

(a) BCMA immunohistochemistry of the caudate nucleus subependymal region (10x magnification, left, scale bar 200 µm). Inset (40x magnification, right, scale bar 50 µm) shows high magnification image of astrocytes (top) and a neuron (bottom) that stained positive for BCMA, whereas surrounding cells were negative. Images shown are representative slides from the caudate nucleus from the patient described in this case report (N = 1). For each region stained, at least 3 slides were available. (b) BCMA immunohistochemistry of selected brain regions as annotated in the patient of interest (left) versus a control brain (right) from a subject who died due to non-neurologic illness (10x magnification (top), scale bar 200 µm and 20x magnification (middle, bottom), scale bar 100 µm). Images shown are representative slides from the patient described in this case report (N = 1), as well as a single control brain (N = 1). For each region stained, at least 3 slides were available. The experiment was repeated in a second control brain with similar results.