TMEM63C and hereditary spastic paraplegia: Functional in cellula studies indicate a rolefor TMEM63C in regulating both endoplasmic reticulum and mitochondrial morphologies.Together, these findings identify autosomal recessive TMEM63C variants asa cause of pure and complex HSP and add to the growing evidence of a fundamentalpathomolecular role of perturbed mitochondrial-endoplasmic reticulum dynamics in motorneurone degenerative diseases.