<qa>  What is the main cause of MECP2 Duplication disorder?MECP2 Duplication disorder affects principally males who have one and rarely more than one additional copy of MECP2 as well as a variable number of other duplicated genes. These males have absent spoken language, shuffling gait, epilepsy, and, in some, frequent upper respiratory infections or sinusitis. Mother of these males are generally normal due to favorable skewing of X-chromosome inactivation, but in some instances may have neurodevelop-mental delays. Effective treatments are lacking. It is critical to develop phenotype-genotype correlations and longitudinal natural history data to assist the conduct of clinical trials. 