The cardinal features of the MECP2 duplication syndrome include early infantile hypotonia, often leading to feeding problems and delayed psychomotor development resulting in severe to profound intellectual disability (ID) with absent to very limited speech and neurological symptoms, including abnormal gait, epilepsy and spasticity.
In the majority of patients, recurrent infections, especially of the respiratory tract occur and often gastro-intestinal motility problems are present, which represent a significant cause of patient morbidity and mortality.
In those patients that underwent brain imaging, 3 in 4 were reported to have structural and even progressive anomalies. However, none of these abnormalities is specific for the disorder.
The syndrome affects males, since most carrier women show skewed X-inactivation and do not have symptoms. However, girls can also be affected, when X-inactivation is unfavorable and these girls normally show milder and more variable symptoms than affected boys.