<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by spondylothoracic dysostosis ? [/INST] Spondylothoracic dysostosis affects about one in 200,000 people worldwide. However, it is much more common in people of Puerto Rican ancestry, affecting approximately one in 12,000 people. </s>