| Summary: | 碩士 === 國立臺灣大學 === 腦與心智科學研究所 === 105 === Objective: Rett syndrome (RTT) is a neurodevelopmental disease that primarily affects girls. It is characterized by trajectory changes in communication, cognition and motor functions. Researches in neuropathology showed some marked changes in total brain volume and cerebral size. To understand the disease-specific pathological changes of brainmicrostructures in RTT, we applied cortical volume data and tract-specific analysis to investigate the alteration of brain microstructure and utilized susceptibility weighted imaging (SWI) to detect abnormal iron accumulation. Methods: We recruited 28 patients and 32 age- and sex-matched healthy controls. All of the scans were acquired by 3 tesla scanner with 32-channel phased array coil. MR imaging consists of sagittal T1-weighted and axial T2 fast spin-echo. A total of 102 diffusion encoding gradients with the maximum diffusion sensitivity were applied in diffusion spectrum imaging (DSI) and SWI sequence with flow compensation was used to acquire high-resolution imaging. Four cortical lobes were compared separately in two age groups for clarifying the regional difference. The volume data were analyzed and extracted from Freesurfer software. The generalized fractional anisotropy (GFA) value of targeted tracts were analyzed from tract-based automatic analysis (TBAA) and calculated by two sample t-test with Bonferroni correction. Signal intensity on the SWI weremeasured on subcortical regions and compared with health controls. Finally, Spearman''s rank correlation coefficient was used in correlation between clinical presentation and brain microstructural alterations. Results: The regional difference in gray matter showed significant decrease in bilateral frontal lobes and parietal lobes in younger patients and general decrease in four lobes in older patients. GFA values in speech-language related tracts were significantly reduced in older RTT patients. The alteration of speech-language-related tracts between the patients with/without speech was only observed in arcuate fasciculus. The comparison of visual perception-related tracts showed no difference in GFA values between younger groups, but showed severe reduction in older patients. Interestingly, the anterior commissure in both RTT groups showed higher GFA value than healthy controls and the integrity revealed a mild association with visual motor function. In addition, the motorrelated fiber tracts in older RTT group showed lower GFA values, primarily located in frontal striatum and callosal fibers. However, the change of the fiber tracts with significant reduction was not correlated with the changes in motor scales. Furthermore, the contrast ratio in SWI showed significantly lower in striatum of RTT. Discussion: To investigate the microstructural alteration in the different age, we found the progressive changes in the cerebral cortex with age and the reductions in fiber tracts. In the light of early delayed speech-language millstone in RTT and the association with speech ability and GFA values, the integrity of arcuate fasciculus can be a language marker for RTT and for follow-up research. The visual perception-related tracts were associated with visual motor function. These may prove the activity-driven increasing in white matter tracts, even suffering from the severe damage of disease. On the other hand, the cortico-basal ganglia-thalamo-cortical loop in RTT was generally impaired though without correlation with the behavioral data. The consequence may be related to complex neuron network and neuron dysfunction in movement. Moreover, we discovered the abnormal iron accumulation in RTT with uncertain reason. Therefore, a longitudinal cohort study is mandatory to elucidate the effect of the subtle change in basal ganglia.
|
|---|
