AFG3L2 and hereditary spastic paraplegia: Both SPG7 and AFG3L2 have been associated with a human neurodegenerative disease: SPG7 loss-of-function mutations cause an autosomal recessive form of hereditary spastic paraplegia (HSP) [6], in which axons of corticospinal neurons and of somatosensory neurons degenerate [7]; AFG3L2 missense mutations have been implied in the autosomal dominant spinocerebellar ataxia SCA28 [8].