Intramembrane particles at the inner (so-called “P”) face by EM with the FF method. No quantitative abnormalities were detected in the 4.1 (−) Madrid case (B), as compared with normal subjects (A). However, regular distribution was lost with many clusters of various sizes in the 4.1 (−) Madrid case (B). Many irregularly and widely open membrane areas with a much smaller number of IMPs were also observed (B). Original magnification × 150,000. Bars indicate 0.1 μm.