NIPA1 and hereditary spastic paraplegia: SPG3A is the second-most prevalent AD form, constituting 10% of registers cases, with the majority of them accounting for pure HSP and with prior onset by the age of 10 [14]; likewise, alterations in SPG6/NIPA1 [15] and SPG8/KIAA0196 [16] are linked with severe spasticity in the AD form.