<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by spastic paraplegia type 8 ? [/INST] The prevalence of all hereditary spastic paraplegias combined is estimated to be 1 to 18 in 100,000 people worldwide. Spastic paraplegia type 8 likely accounts for only a small percentage of all spastic paraplegia cases. </s>