Roth Mark, Ronco Lucienne, Cadavid Diego, Durbin-Johnson Blythe, Hagerman Randi J, Tassone Flora
Fulcrum Therapeutics, Cambridge, MA 02139, USA.
Division of Biostatistics, University of California Davis, School of Medicine, Davis, CA 95616, USA.
Diagnostics (Basel). 2021 Sep 28;11(10):1780. doi: 10.3390/diagnostics11101780.
Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. FXS is an X-linked, neurodevelopmental disorder caused by a CGG trinucleotide repeat expansion in the 5' untranslated region (UTR) of the Fragile X Mental Retardation gene, . Greater than 200 CGG repeats results in epigenetic silencing of the gene leading to the deficiency or absence of Fragile X mental retardation protein (FMRP). The loss of FMRP is considered the root cause of FXS. The relationship between neurological function and FMRP expression in peripheral blood mononuclear cells (PBMCs) has not been well established. Assays to detect and measure and FMRP have been described; however, none are sufficiently sensitive, precise, or quantitative to properly characterize the relationships between cognitive ability and CGG repeat number, mRNA expression, or FMRP expression measured in PBMCs. To address these limitations, two novel immunoassays were developed and optimized, an electro-chemiluminescence immunoassay and a multiparameter flow cytometry assay. Both assays were performed on PMBCs isolated from 27 study participants with CGG repeats ranging from normal to full mutation. After correcting for methylation, a significant positive correlation between CGG repeat number and mRNA expression levels and a significant negative correlation between FMRP levels and CGG repeat expansion was observed. Importantly, a high positive correlation was observed between intellectual quotient (IQ) and FMRP expression measured in PBMCs.
脆性X综合征（FXS）是遗传性智力残疾最常见的形式。FXS是一种X连锁的神经发育障碍，由脆性X智力低下基因5'非翻译区（UTR）中的CGG三核苷酸重复扩增引起。超过200个CGG重复会导致该基因的表观遗传沉默，从而导致脆性X智力低下蛋白（FMRP）缺乏或缺失。FMRP的缺失被认为是FXS的根本原因。外周血单核细胞（PBMCs）中神经功能与FMRP表达之间的关系尚未完全明确。已有检测和测量[相关内容]及FMRP的方法被描述；然而，没有一种方法足够灵敏、精确或定量，无法正确表征认知能力与PBMCs中CGG重复数、[相关基因]mRNA表达或FMRP表达之间的关系。为了解决这些局限性，开发并优化了两种新型免疫测定法，一种是电化学发光免疫测定法，另一种是多参数流式细胞术测定法。这两种测定法都在从27名研究参与者中分离出的PBMCs上进行，这些参与者的CGG重复数范围从正常到完全突变。在对甲基化进行校正后，观察到CGG重复数与[相关基因]mRNA表达水平之间存在显著正相关，FMRP水平与CGG重复扩增之间存在显著负相关。重要的是，在PBMCs中测量的智商（IQ）与FMRP表达之间观察到高度正相关。
