Furthermore, the growing number of genes associated to allelic variant of HSP/ALS or HSP evolving to ALS, such as CYP7B1, KIF5A, spatacsin, ERLIN1, and ALS2, reiterate the question if these are two distinct entities or rather a spectrum of motor neuron involvement [31]. This evidence concerns the gene CYP7B1 and amyotrophic lateral sclerosis.