MCU and myopathy: MPXPS has been reported in 41 cases (Table S1) and presents with myopathy, learning disability, and extrapyramidal movement disorder.4, 5, 6, 7, 8, 9, 10, 11, 12 The MICU1 protein regulates calcium influx into mitochondria through interaction with the mitochondrial calcium uniporter (MCU).