Fragile X syndrome (FXS) is the leading monogenetic cause of autism spectrum disorder and inherited cause of intellectual disability that affects approximately one in 7,000 males and one in 11,000 females. In FXS, the Fmr1 gene is silenced and prevents the expression of the fragile X mental retardation protein (FMRP) that directly targets mRNA transcripts of multiple GABA_A subunits. Therefore, FMRP loss adversely impacts the neuronal firing of the GABAergic system which creates an imbalance in the excitatory/inhibitory ratio within the brain. Current FXS treatment strategies focus on curing symptoms, such as anxiety or decreased social function. While treating symptoms can be helpful, incorporating non-invasive imaging to evaluate how treatments change the brain’s biology may explain what molecular aberrations are associated with disease pathology. Thus, the GABAergic system is suitable to explore developing novel therapeutic strategies for FXS. To understand how the GABAergic system may be affected by this loss-of-function mutation, GABA concentrations were examined within the frontal cortex and thalamus of 5-day-old wild type and Fmr1 knockout mice using both ¹H magnetic resonance imaging (¹H-MRS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Our objective was to develop a reliable scanning method for neonatal mice in vivo and evaluate whether ¹H-MRS is suitable to capture regional GABA concentration differences at the front end of the critical cortical period where abnormal neurodevelopment occurs due to FMRP loss is first detected. ¹H-MRS quantified GABA concentrations in both frontal cortex and thalamus of wild type and Fmr1 knockout mice. To substantiate the results of our ¹H-MRS studies, in vitro LC-MS/MS was also performed on brain homogenates from age-matched mice. We found significant changes in GABA concentration between the frontal cortex and thalamus within each mouse from both wild type and Fmr1 knockout mice using ¹H-MRS and LC-MS/MS. Significant GABA levels were also detected in these same regions between wild type and Fmr1 knockout mice by LC-MS/MS, validating that FMRP loss directly affects the GABAergic system. Thus, these new findings support the need to develop an effective non-invasive imaging method to monitor novel GABAergic strategies aimed at treating patients with FXS.

脆性 X 综合征 (FXS) 是自闭症谱系障碍的主要单基因原因，也是智力障碍的遗传原因，大约影响 7,000 分之一的男性和 11,000 分之一的女性。在 FXS 中，FMR1_{基因沉默并阻止直接靶向多个 GABA A}的 mRNA 转录本的脆性 X 智力低下蛋白 (FMRP) 的表达亚单位。因此，FMRP 损失会对 GABAergic 系统的神经元放电产生不利影响，从而导致大脑内兴奋/抑制比失衡。目前的 FXS 治疗策略侧重于治愈症状，例如焦虑或社交功能下降。虽然治疗症状可能会有所帮助，但结合非侵入性成像来评估治疗如何改变大脑生物学可能会解释哪些分子畸变与疾病病理学相关。因此，GABAergic 系统适合探索开发新的 FXS 治疗策略。为了了解 GABA 能系统如何受到这种功能丧失突变的影响，在 5 日龄野生型和FMR1使用¹ H 磁共振成像 ( ¹ H-MRS) 和液相色谱-串联质谱法 (LC-MS/MS) 对基因敲除小鼠进行分析。我们的目标是为新生小鼠开发一种可靠的扫描方法体内并评估¹ H-MRS 是否适合捕获关键皮层期前端的局部 GABA 浓度差异，其中首先检测到由于 FMRP 丢失而发生异常神经发育。¹ H-MRS 量化了野生型和野生型的额叶皮层和丘脑中的 GABA 浓度FMR1基因敲除小鼠。^{为了证实我们的1} H-MRS 研究结果，体外还对来自年龄匹配小鼠的脑匀浆进行了 LC-MS/MS。我们发现野生型和野生型小鼠的额叶皮层和丘脑之间的 GABA 浓度发生显着变化FMR1使用¹ H-MRS 和 LC-MS/MS 敲除小鼠。在野生型和野生型之间的这些相同区域中也检测到显着的 GABA 水平FMR1通过 LC-MS/MS 敲除小鼠，验证 FMRP 损失直接影响 GABAergic 系统。因此，这些新发现支持需要开发一种有效的非侵入性成像方法来监测旨在治疗 FXS 患者的新型 GABAergic 策略。