SPG11 and juvenile amyotrophic lateral sclerosis: PRX, RETREG1, and SPG11 genes are associated with autosomal recessive Charcot-Marie-Tooth disease type 4F, autosomal recessive hereditary sensory and autonomic neuropathy type 2B, and autosomal recessive hereditary spastic paraplegia 11 (SPG11), juvenile amyotrophic lateral sclerosis 5 and Charcot-Marie-Tooth disease type 2X, respectively.