Adamczyk Abby, Gause Colin D, Sattler Rita, Vidensky Svetlana, Rothstein Jeffery D, Singer Harvey, Wang Tao
McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Psychiatr Genet. 2011 Apr;21(2):90-7. doi: 10.1097/YPG.0b013e328341a307.
Abnormalities in neurotransmission within the cortico-striatal-thalamo-cortical circuitry are implicated in the pathogenesis of Tourette syndrome. Glutamate is a major excitatory neurotransmitter and an important member in the cortico-striatal-thalamo-cortical circuitry. To explore the role of glutamatergic neurotransmission in genetic susceptibility of Tourette syndrome, we carried out the genetic and functional characterization of sequence variants in SLC1A3 gene, which encodes the main glutamate transporter in astrocytes in individuals with well-characterized Tourette syndrome (n=256) and normal controls (n=224).
Exon-containing regions of SLC1A3 gene were screened using capillary electrophoresis-single strand conformation polymorphism followed by direct sequencing. Sequence variants were genotyped by restriction enzyme digestion and studied using glutamate uptake assay and membrane protein pull-down for transporter function.
A missense variant involving a highly conserved residue, E219D, was identified in 11 heterozygous individuals with Tourette syndrome and four in the controls. The allele frequency for E219D was 2.4 folds higher in the Tourette syndrome (0.022) compared with the control cohort (0.009) although the difference did not reach statistical significance in the current cohorts (P=0.09). A H-glutamate-uptake assay showed that E219D conveys a significant increase (1.66 fold) in the SLC1A3-mediated glutamate uptake in HEK293 cells. A biotin-mediated membrane pull-down analysis showed a similar increase (1.5 fold) of mutant SLC1A3 protein in the membrane fraction of transfected HEK293 cells compared with that in the wild type controls.
These results indicate that E219D is a functional SLC1A3 variant that is presented in a small number of individuals with Tourette syndrome. Further studies on possible changes in glutamate transport in the pathogenesis of Tourette syndrome are warranted.
皮质-纹状体-丘脑-皮质环路中的神经传递异常与抽动秽语综合征的发病机制有关。谷氨酸是一种主要的兴奋性神经递质，也是皮质-纹状体-丘脑-皮质环路的重要组成部分。为了探讨谷氨酸能神经传递在抽动秽语综合征遗传易感性中的作用，我们对SLC1A3基因的序列变异进行了遗传和功能特征分析，该基因编码星形胶质细胞中的主要谷氨酸转运体，研究对象为确诊的抽动秽语综合征患者（n = 256）和正常对照（n = 224）。
采用毛细管电泳-单链构象多态性技术对SLC1A3基因的含外显子区域进行筛选，随后进行直接测序。通过限制性酶切对序列变异进行基因分型，并利用谷氨酸摄取试验和膜蛋白下拉法研究转运体功能。
在11名杂合子抽动秽语综合征患者中鉴定出一个涉及高度保守残基E219D的错义变异，对照组中有4人携带该变异。尽管在当前队列中差异未达到统计学意义（P = 0.09），但E219D的等位基因频率在抽动秽语综合征患者中（0.022）是对照组（0.009）的2.4倍。H-谷氨酸摄取试验表明，E219D使HEK293细胞中SLC1A3介导的谷氨酸摄取显著增加（1.66倍）。生物素介导的膜下拉分析显示，与野生型对照相比，转染的HEK293细胞膜部分中突变型SLC1A3蛋白增加了类似的倍数（1.5倍）。
这些结果表明，E219D是一种功能性SLC1A3变异，存在于少数抽动秽语综合征患者中。有必要进一步研究抽动秽语综合征发病机制中谷氨酸转运可能的变化。
