EC-1 | Loss of Function of Maternal Effect Genes: A New Cause of Feto-Placental Developmental Defects and Congenital Anomalies

Momal Sharif¹, Roni Zemet², Zahra Anvar¹, Imen Chakchouk², Ignatia Van den Veyver³

¹Obstetrics and Gynecology, Baylor College of Medicine, Houston, Texas, USA; ²Baylor College of Medicine, Houston, Texas, USA; ³Obstetrics and Gynecology and Molecular and Human Genetics, Baylor College, Houston, Texas, USA

Objectives: Congenital anomalies affect 3%–6% of all pregnancies and are a leading cause of infant mortality. When genetic testing by trio exome sequencing is done to find a genetic etiology, the analysis focuses on identifying causative variants in the proband’s sample. Parental sequences are primarily analyzed to support the interpretation of significant findings in the proband. Recent animal data and rare human multilocus imprinting disorders have highlighted that inactivating variants in the maternal genome, in certain maternal effect genes (MEGs), can cause developmental phenotypes in offspring. We conducted a detailed characterization of the developmental defects caused by maternal loss of Nlrp2, a MEG, in a mouse model. Nlrp2 encodes a member of the subcortical maternal complex of oocytes and preimplantation embryos important for preimplantation embryo development.

Methods: We studied an Nlrp2-knock-out (KO) mouse model. We set up 5–14 timed matings each for the following crosses: wildtype (WT) × WT, maternal KO × WT, and WT × paternal KO. At embryonic day E11.5, dams were euthanized, and concepti (n = 20–29, 6–8 matings per cross) were examined for gross structural anomalies, yolk sac vascularization, and placental layers. We used a novel application of X-ray microcomputed tomography for comprehensive placental, embryonic, and yolk sac characterization at 3 μm/voxel.

Results: Compared to control pregnancies from WT × WT and WT × paternal-KO matings, pregnant KO females had increased resorptions of concepti (n = 25, p = 0.0179). Ongoing pregnancies had embryonic and placental defects. Placentas were smaller, with irregular lacunae, extensions, and infoldings of decidua, abnormal junctional zone, and compact labyrinth with variations in vasculature. There was also abnormal yolk sac vasculature (n = 26, 40.2%) and irregular amniotic cavities (n = 26, p = 0.0491). Embryos had axis abnormalities (n = 29, 13.7%), craniofacial anomalies (n = 29, 31%), and congenital heart defects (n = 29, 58.6%).

Conclusions: These findings show that maternal loss of Nlrp2 causes extraembryonic and embryonic defects. These include congenital anomalies such as craniofacial, embryonic axis, limb, neural closure, and heart defects, and confirm that maternal loss of MEGs can cause birth defects. This warrants further investigations in humans with unexplained congenital anomalies. Our study illustrates the power of animal models to define and characterize the types of birth defects that can result from MEGs, which can support human studies.

中文翻译：

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ISPD 第 27 届国际产前诊断与治疗会议口头摘要，英国爱丁堡，2023 年 6 月 19-21 日

EC-1 | 母体效应基因功能丧失：胎儿胎盘发育缺陷和先天性异常的新原因

莫马尔·谢里夫¹、罗尼·泽米特²、扎赫拉·安瓦尔¹、伊门·恰克乔克²、伊格纳蒂亚·范·登·维弗³

¹美国德克萨斯州休斯顿贝勒医学院妇产科； ²贝勒医学院，美国德克萨斯州休斯顿； ³妇产科和分子与人类遗传学，贝勒学院，休斯敦，德克萨斯州，美国

目标：先天性异常影响所有妊娠的 3%–6%，是婴儿死亡的主要原因。当通过三重外显子组测序进行基因检测来寻找遗传病因时，分析的重点是识别先证者样本中的致病变异。主要分析亲本序列以支持对先证者的重要发现的解释。最近的动物数据和罕见的人类多位点印记疾病强调，母体基因组中某些母体效应基因（MEG）的失活变异可能会导致后代的发育表型。我们对小鼠模型中Nlrp2 （一种 MEG ）母体缺失引起的发育缺陷进行了详细表征。Nlrp2编码卵母细胞和植入前胚胎皮质下母体复合体的成员，对植入前胚胎发育很重要。

方法：我们研究了Nlrp2敲除 (KO) 小鼠模型。我们为以下杂交分别设置了 5-14 次定时交配：野生型 (WT) × WT、母本 KO × WT 和 WT × 父本 KO。在胚胎 E11.5 天，对母鼠实施安乐死，并检查受胎（n = 20-29，每次杂交 6-8 次交配）的总体结构异常、卵黄囊血管化和胎盘层。我们使用 X 射线微计算机断层扫描的新颖应用，以 3 μm/体素对胎盘、胚胎和卵黄囊进行全面表征。

结果：与 WT × WT 和 WT × 父本-KO 交配的对照妊娠相比，妊娠 KO 雌性的受孕吸收增加（n = 25，p = 0.0179）。正在进行的妊娠存在胚胎和胎盘缺陷。胎盘较小，有不规则的腔隙、蜕膜的延伸和内折、异常的交界区和血管系统变化的致密迷路。还存在卵黄囊脉管系统异常 ( n = 26, 40.2%) 和不规则羊膜腔 ( n = 26, p = 0.0491)。胚胎存在轴异常 ( n = 29, 13.7%)、颅面异常 ( n = 29, 31%) 和先天性心脏缺陷 ( n = 29, 58.6%)。

结论：这些发现表明，母体Nlrp2缺失会导致胚胎外和胚胎缺陷。这些包括先天性异常，如颅面、胚胎轴、肢体、神经闭合和心脏缺陷，并证实母体 MEG 缺失可能导致出生缺陷。这需要对患有无法解释的先天异常的人类进行进一步的研究。我们的研究说明了动物模型在定义和表征 MEG 可能导致的出生缺陷类型方面的能力，这可以支持人类研究。