<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by X-linked spondyloepiphyseal dysplasia tarda ? [/INST] The prevalence of X-linked spondyloepiphyseal dysplasia tarda is estimated to be 1 in 150,000 to 200,000 people worldwide. </s>