Hereditary spastic paraplegia type 5 (SPG5), like ALS, is a form of motor neuron disease, but unlike ALS, it is a monogenic disease resulting from a deficiency in CYP7B1 (cytochrome P450 family 7 subfamily B member 1), the oxysterol 7α-hydroxylase (Figure 1) [18,35]. Here, CYP7B1 is linked to motor neuron disorder.