| Abstract: | 瑞特氏症 (Rett Syndrome, RTT) 是一種主要發生在女性幼童的神經發育疾病。典型RTT 患者在出生時多為正常，症狀通常在出生後6-18 個月逐漸顯現，主要包括運動技能退化、語言能力缺失，接著出現手部絞動之刻板行為，行動困難以及自閉特徵。然而，在RTT 患者中有大約25-32%在出生後前3 個月即出現癲癇發作，因此被歸類為「非典型RTT」。研究發現，X 染色體上的甲基CpG 結合蛋白2（MeCP2）基因突變發生在超過95%的典型RTT 病例中，卻只發生在20-40%的非典型RTT 患者上，顯示非典型RTT 可能肇因於其他的遺傳因子。最近的研究發現，第五型細胞週期類蛋白磷酸激酶(cyclin-dependent kinase-like 5,簡稱CDKL5)基因的突變發生在許多非典型RTT 病例中。CDKL5 基因亦位於X 染色體上，負責製造一種絲胺酸/ 蘇胺酸蛋白磷酸激酶，於出生後早期大量表現於成熟神經細胞中，可負責調控皮質神經元的樹突形成；但目前仍不知是否CDKL5 的缺失會導致非典型RTT 的發生。吾人假設CDKL5 之缺失為非典型RTT 的致病因素，故於本計畫中將首先分析CDKL5 基因剔除小鼠之行為表現，建立一個新的非典型RTT 之小鼠模式。基於CDKL5 為一種蛋白磷酸激酶，CDKL5 缺失將可能干擾下游分子之訊息傳遞，影響正常的神經傳導與神經發育，進而導致小鼠表現出類似非典型RTT 之症狀；本計畫接下來將利用Cdkl5 基因剔除小鼠，分析CDKL5 的缺失在神經解剖、神經化學以及神經發育上所造成的改變。最後，我們將比較CDKL5 與MeCP2 基因剔除小鼠在分子與細胞層次的表現型，藉以推測此二分子之間可能的交互作用，並釐清典型與非典型RTT 之間共同之致病機轉。本研究將不只建立一個研究非典型RTT 的小鼠模式，也對RTT 致病機轉提供細胞及分子層面的了解。最終希望本研究有助於發展治療RTT 的有效策略。
Rett Syndrome (RTT) is a severe neurodevelopmental disorder that primarily affects girls during early childhood. Patients with classic RTT (cRTT) are usually born healthy and then develop symptoms after 6-18 months of age. The symptoms include hypotonia, loss of speech and purposeful motor skills, stereotypic hand wringing, ataxia and the appearance of autistic traits. About 25-32% of RTT patients, however, experience seizures in the first three months of life and thus are considered as atypical RTT (aRTT) or RTT variant forms. Mutations in the X-linked gene encoding methyl-CpG binding protein (MECP2) are found in more than 95% of patients with cRTT, but only in 20-40% of patients with aRTT, suggesting that other genetic causes may exist for aRTT. In accordance with this idea, recent genetic studies have reported mutations in the cyclin-dependent kinase-like 5 (CDKL5) gene in many cases of aRTT. CDKL5 is also an X-linked gene encoding a putative serine-threonine kinase. The CDKL5 expression is developmentally up-regulated at early postnatal stage, highly enriched in mature neurons, and recently implicated in the modulation of dendritic morphogenesis of cortical neurons. However, it remains to be determined whether defect in CDKL5 would cause aRTT. We hypothesize that CDKL5 deficiency is account for the pathogenesis of aRTT. Thus, within the scope of this proposal, we plan to address this hypothesis in a newly developed Cdkl5 knockout mouse model. We will characterize the behavioral phenotypes associated with CDKL5 loss-of-function in our specific aim 1, and hope to establish a valid animal model for aRTT. Given the putative kinase feature of CDKL5, we postulate that loss-of-function of CDKL5 may disrupt downstream signaling cascades critical for neurotransmission and neural development, thereby leading to aRTT-like symptoms in mice. We will examine the anatomical and neurochemical phenotypes associated with Cdkl5 knockout mice and investigate the role of CDKL5 in neural development in our specific aim 2. Finally, we will compare the molecular phenotypes between Cdkl5 and Mecp2 knockout mice, investigate the interaction between CDKL5 and MeCP2, and hope to reveal the common pathogenic mechanisms between cRTT and aRTT. Our study would not only establish a valid genetic mouse model to study aRTT, but also gain insights into the molecular and cellular basis of RTT. Ultimately, our study could provide potential therapeutic strategies to medicate RTT. |
