ATL1 and hereditary spastic paraplegia: For example, we found that there were eight studies which reported a frequency of ATL1 gene mutations less than 15%: 2.9% [27] in ADHSP families, 3.7% in ADSHP probands [45], 4.2% in HSP families [36], 8.3% in unrelated early onset pure ADHSP families [9], 6.6% in a heterogeneous population including both pure and complicated HSP phenotypes [21], 8.6% in ADHSP families [29], 11.3% in the ADHSP families [32], and 11.7% in ADHSP probands [44].