<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by MECP2 duplication syndrome ? [/INST] The prevalence of MECP2 duplication syndrome is unknown; approximately 120 affected individuals have been reported in the scientific literature. It is estimated that this condition is responsible for 1 to 2 percent of all cases of intellectual disability caused by changes in the X chromosome. </s>