ATL1 and hereditary spastic paraplegia: We also found four studies which reported a higher frequency of ATL1 gene mutations: 20.0% in pure HSP [55], 20.0% (3/15) in early onset autosomal dominant HSP [13], 38.5% in SPG4-negative pure ADHSP families [11], and 38.7% in pure ADHSP families [15].