Department of Obstetrics and Gynecology, National Clinical Research Center for Obstetric and Gynecologic Diseases, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China.
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX; Medical Scientist Training Program, Baylor College of Medicine, Houston, TX.
Genet Med. 2022 Nov;24(11):2262-2273. doi: 10.1016/j.gim.2022.08.012. Epub 2022 Sep 16.
Mayer-Rokitansky-Küster-Hauser syndrome (MRKHS) is characterized by congenital absence of the uterus, cervix, and the upper part of the vagina in females. Whole-gene deletion and loss-of-function variants in TBX6 have been identified in association with MRKHS. We aimed to expand the spectrum of TBX6 variants in MRKHS and explore the biological effect of the variant alleles.
Rare variants in TBX6 were called from a combined multiethnic cohort of 622 probands with MRKHS who underwent exome sequencing or genome sequencing. Multiple in vitro functional experiments were performed, including messenger RNA analysis, western blotting, transcriptional activity assay, and immunofluorescence staining.
We identified 16 rare variants in TBX6 from the combined cohort, including 1 protein-truncating variant reported in our previous study and 15 variants with unknown effects. By comparing the prevalence of TBX6 variants in the Chinese MRKHS cohort vs 1038 female controls, we observed a significant mutational burden of TBX6 in affected individuals (P = .0004, odds ratio = 5.25), suggesting a causal role of TBX6 variants in MRKHS. Of the 15 variants with uncertain effects, 7 were shown to induce a loss-of-function effect through various mechanisms. The c.423G>A (p.Leu141=) and c.839+5G>A variants impaired the normal splicing of TBX6 messenger RNA, c.422T>C (p.Leu141Pro) and c.745G>A (p.Val249Met) led to decreased protein expression, c.10C>T (p.Pro4Ser) and c.400G>A (p.Glu134Lys) resulted in perturbed transcriptional activity, and c.356G>A (p.Arg119His) caused protein mislocalization. We observed incomplete penetrance and variable expressivity in families carrying deleterious variants, which indicates a more complex genetic mechanism than classical Mendelian inheritance.
Our study expands the mutational spectrum of TBX6 in MRKHS and delineates the molecular pathogenesis of TBX6 variants, supporting the association between deleterious variants in TBX6 and MRKHS.
Mayer-Rokitansky-Küster-Hauser 综合征（MRKHS）的特征是女性先天性子宫、宫颈和阴道上段缺失。TBX6 基因的全基因缺失和功能丧失变异与 MRKHS 相关。我们旨在扩大 MRKHS 中 TBX6 变异的谱，并探讨变异等位基因的生物学效应。
从接受外显子组测序或基因组测序的 622 名 MRKHS 先证者的联合多民族队列中，对 TBX6 中的罕见变异进行了检测。进行了多种体外功能实验，包括信使 RNA 分析、western blot、转录活性测定和免疫荧光染色。
我们从联合队列中鉴定出 16 个 TBX6 中的罕见变异，包括我们之前研究中报道的 1 个蛋白截断变异和 15 个未知效应的变异。通过比较中国 MRKHS 队列与 1038 名女性对照中 TBX6 变异的患病率，我们观察到受影响个体中 TBX6 的突变负担显著（P=0.0004，优势比=5.25），表明 TBX6 变异在 MRKHS 中起因果作用。在 15 个不确定效应的变异中，有 7 个通过各种机制导致功能丧失效应。c.423G>A(p.Leu141=)和 c.839+5G>A 变异破坏了 TBX6 信使 RNA 的正常剪接，c.422T>C(p.Leu141Pro)和 c.745G>A(p.Val249Met)导致蛋白表达减少，c.10C>T(p.Pro4Ser)和 c.400G>A(p.Glu134Lys)导致转录活性改变，c.356G>A(p.Arg119His)导致蛋白定位异常。我们观察到携带有害变异的家系中存在不完全外显率和可变表达性，这表明比经典孟德尔遗传更复杂的遗传机制。
我们的研究扩展了 MRKHS 中 TBX6 的突变谱，并描绘了 TBX6 变异的分子发病机制，支持 TBX6 中有害变异与 MRKHS 之间的关联。
