蕾特氏症（瑞特氏症候群、Rett Syndrome、RTT），是一种X染色体性联显性遗传疾病，突变点位于MeCP2基因上，属于罕见神经疾病，发病率约为1/12,000～1/15,000，而且临床表征缺乏特殊性，因此诊断上十分困难。蕾特氏症是由Dr.Andreas Rett所发现，并发表于1966年，后人将此病以Rett命名。此病尚未有治疗方法，现阶段主要是针对出现的病症进行复健治疗。

蕾特氏症，好发于女性婴孩或幼童 ，病童会有神经急速退化、发展迟缓的现象，而男性患者几乎无法存活。患者于出生至6～18个月内，生长发育与常人一样。刚开始发病时，初始症状有翻白眼、婴儿失去吸吮反射、不规则转头、运动发展障碍等现象发生，有些初始症状与普瑞德威利症候群出现重叠，加上文献数据极为稀少，故难以判明症状。之后，开始出现神经失调：运动能力渐渐消失、失去语言能力、正确的反射能力、便秘，也可以经脑部扫描发现脑皮质萎缩的情形，在生活中也经常发生痉挛、癫痫等神经阈值低下的症状。

Rett syndrome (RTT), originally termed cerebroatrophic hyperammonemia, is a rare genetic postnatal neurological disorder of the grey matter of the brain that almost exclusively affects females but has also been found in male patients. The clinical features include small hands and feet and a deceleration of the rate of head growth (including microcephaly in some). Repetitive stereotyped hand movements, such as wringing and/or repeatedly putting hands into the mouth, are also noted. People with Rett syndrome are prone to gastrointestinal disorders and up to 80% have seizures. They typically have no verbal skills, and about 50% of affected individuals do not walk. Scoliosis, growth failure, and constipation are very common and can be problematic.