The face that you see in the mirror each morning is likely the product of precision in cell behavior, balanced molecular regulation, and a nurturing environment relatively free from toxins or teratogens. Dr. Chengji Zhou and team from UC Davis provide us with four comprehensive reviews on aspects of orofacial clefts (OFCs) to bring us up to date on how our face develops and what happens when these processes are disrupted. Drs. Yulai Zhou and Julian Little and team from the Universities of Ottawa and Dundee and Duke evaluated the data that folic acid supplementation may effectively prevent OFCs. The study of OFCs could provide a better understanding of developmental programs common to the morphogenesis of a variety of embryonic structures, as well as in identifying therapeutic strategies specific to OFC prevention.

OFCs are the most common of craniofacial birth defects and one of the most common of all birth defects, affecting on average 1 in 700 newborns worldwide (Mossey & Modell, 2012). OFCs include the failure of the upper lip and/or palate (the roof of the mouth) to close properly during development, leaving a gap or gaps that often require surgical closure. Aside from the psychosocial consequences of OFCs that are not trivial (Al‐Namankany & Alhubaishi, 2018; Broder, Smith, & Strauss, 1994; Hunt, Burden, Hepper, & Johnston, 2005), difficulties in eating, speaking, and breathing can result from OFCs (Goswami, Bhushan, & Jangra, 2016). These individuals also have higher risk for ear infections and dental issues.

In humans, orofacial formation is mostly active from the fourth through sixth week of embryonic development (Schoenwolf, Bleyl, Brauer, & Francis‐West, 2014). Face formation occurs in mice at embryonic days 8–14.5 (Tamarin & Boyde, 1977), in zebrafish during 36–48 hr postfertilization (hpf; Swartz, Sheehan‐Rooney, Dixon, & Eberhart, 2011), and in chicken at incubation of 3–6.5 days (HH stages 20–29; Abramyan & Richman, 2018).

The typical face is the result of several primordial tissues growing in concert and fusing at just the right time and place (Figure 1). These tissues are largely derived from or orchestrated by neural crest cell (NCC) progenitors in communication with surrounding epithelia. The NCCs proliferate and migrate while receiving and sending signals (Helms, Cordero, & Tapadia, 2005). After migration, they differentiate into a wide range of cell types. The cranial NCC derivatives form mounds of mesenchymal tissues covered by epithelial cells that are called prominences or processes that fuse with each other in a stereotyped way to form orofacial structures and separate oral and nasal chambers. Each step occurs with bilateral symmetry. Ji et al. (2020) explain and explore many cellular events that are involved in the development of the normal face and which ones are disrupted in OFCs.

In view of the complexity of face development, it is not surprising that networks of genes and factors have been implicated in its malformation. Reynolds et al. clarify this complexity and provide comprehensive tables of the conditions and associated or candidate genes.

OFCs can be found as isolated defects or as part of syndromes. The genetic causes of syndromic OFCs are easier to track than isolated OFCs. For example, 68% of individuals with Van der Woude syndrome and 97% of families with popliteal pterygium syndrome have mutations in the interferon regulatory factor 6 (IRF6) gene (1q32.2‐q32.3) that transcribes a transcription factor involved in many developmental processes, including epidermal development (de Lima et al., 2009). It is expressed in the orofacial epithelial cells to maintain epithelial integrity and prevent ectopic epithelial fusions during palatogenesis.

“Modern sequencing technologies have accelerated our ability to identify specific sequences and variants that are linked with clefts, and at least 350 candidate genes have been identified through association studies in human OFC patients alone.”

However, the genomic DNA sequence needs no change at all to initiate OFCs. Regulating access of transcriptional machinery to DNA sequences can be powerful in itself. The epigenetic causes of OFCs are presented by Garland and colleagues. Epigenetics has a significant impact on OFC pathogenesis. Conformational changes to the DNA after methylation allow or prohibit binding of the transcriptional machinery. Other epigenetic factors include histone modifications and noncoding RNAs (such as miRNA), which also play important roles in OFC etiology.

Embryos are highly vulnerable to environmental factors such as maternal smoking, alcohol intake, poor diet, overheating, and exposure to drugs and pollutants. These environmental factors can cause developmental disorders including OFCs and can also have transgenerational consequences. Embryonic face development is not only vulnerable to in utero exposure but is also affected by exposures to the mother and even the father before pregnancy. Maternal and paternal environmental effects can be transferred as epigenetic marks that can manifest as OFCs in the embryo without direct in utero exposure. While we know that some of these negative environmental factors can be eliminated, others cannot be avoided. Can the research help to protect us from OFCs through other avenues such as with the use of preconception and prenatal supplements?

Drs. Yulai Zhou, Julian Little, and collaborators from the Universities of Ottawa and Dundee and Duke provide a set of meta‐analyses to determine the relationship between different indicators of folate intake/status and OFCs. Since the last such analysis published in 2008 (Johnson & Little, 2008), 56 papers published in the years 2007–2020 were identified. Based on the 2008 study, the conclusion was that there was an 18% decline in the risk of cleft lip/cleft palate (CL/P) associated with the use of folic acid containing supplements but no significant reduction in cleft palate (CP). They also reported a reduction of about 23% in CL/P risk with intake of multivitamins. The updated findings suggest that taking multivitamin supplements that include folic acid during periconception may prevent CL/P, reducing the risk by 40%, and CP only, reducing the risk by 19%. Folic acid supplementation alone did not seem to help. The update differs from the 2008 study in that study participants were from a wider range of countries, broadening the socioeconomic variability. Comparison across these meta‐analyses illustrates the difficulties inherent in these types of analyses and the need for more studies to get a clearer picture of just what is needed to prevent OFCs. Nonetheless, the good news is that supplements appear to be effective in preventing some OFCs.

你每天早上在镜子里看到的脸很可能是细胞行为精确、分子调节平衡以及相对没有毒素或致畸剂的养育环境的产物。加州大学戴维斯分校的 Chengji Zhou 博士和团队为我们提供了四项关于口裂 (OFC) 方面的综合评论，让我们了解我们的面部如何发育以及当这些过程被破坏时会发生什么。博士 来自渥太华大学和邓迪大学和杜克大学的 Yulai Zhou 和 Julian Little 及其团队评估了补充叶酸可以有效预防 OFC 的数据。OFC 的研究可以更好地了解各种胚胎结构形态发生的共同发育程序，以及确定特定于 OFC 预防的治疗策略。

OFC 是最常见的颅面先天缺陷，也是所有先天缺陷中最常见的一种，全世界平均每 700 名新生儿中就有 1 人受到影响 (Mossey & Modell, 2012 )。OFC 包括上唇和/或上颚（口腔顶部）在发育过程中未能正确闭合，留下一个或多个通常需要手术闭合的间隙。除了 OFC 的社会心理后果（Al-Namankany & Alhubaishi，2018 年；Broder、Smith 和 Strauss，1994 年；Hunt、Burden、Hepper 和 Johnston，2005 年）之外，进食、说话和呼吸困难可能OFC 的结果（Goswami、Bhushan 和 Jangra，2016 年）。这些人患耳部感染和牙齿问题的风险也更高。

在人类中，口面部形成在胚胎发育的第四周到第六周最为活跃（Schoenwolf、Bleyl、Brauer 和 Francis-West，2014 年）。在胚胎第 8-14.5 天的小鼠中（Tamarin & Boyde，1977），在受精后 36-48 小时的斑马鱼中（hpf；Swartz，Sheehan-Rooney，Dixon，& Eberhart，2011），以及在孵化的鸡中出现面部形成3-6.5 天（HH 阶段 20-29；Abramyan 和 Richman，2018 年）。

典型的面部是几个原始组织在正确的时间和地点协同生长和融合的结果（图 1）。这些组织主要来源于与周围上皮细胞相通的神经嵴细胞 (NCC) 祖细胞或由它们协调。NCC 在接收和发送信号的同时增殖和迁移 (Helms, Cordero, & Tapadia, 2005 )。迁移后，它们分化为多种细胞类型。颅骨 NCC 衍生物形成被上皮细胞覆盖的间充质组织堆，称为突起或突起，它们以刻板的方式相互融合以形成口面部结构并分离口腔和鼻腔。每一步都以双边对称发生。姬等人。( 2020) 解释和探索许多参与正常面部发育的细胞事件，以及哪些在 OFC 中被破坏。

鉴于面部发育的复杂性，基因和因素网络与它的畸形有关也就不足为奇了。雷诺兹等人。阐明这种复杂性并提供条件和相关或候选基因的综合表格。

OFC 可以作为孤立的缺陷或作为综合征的一部分被发现。综合征性 OFC 的遗传原因比孤立的 OFC 更容易追踪。例如，68% 的 Van der Woude 综合征患者和 97% 的腘腘综合征家族的干扰素调节因子 6 (IRF6) 基因 (1q32.2-q32.3) 发生突变，该基因转录参与许多发育过程，包括表皮发育（de Lima et al., 2009）。它在口面部上皮细胞中表达，以维持上皮完整性并防止腭发生过程中的异位上皮融合。

“现代测序技术加速了我们识别与裂隙相关的特定序列和变异的能力，仅通过人类 OFC 患者的关联研究，就已经确定了至少 350 个候选基因。”

然而，基因组 DNA 序列根本不需要改变即可启动 OFC。调节转录机制对 DNA 序列的访问本身就很强大。Garland 及其同事提出了 OFC 的表观遗传原因。表观遗传学对 OFC 发病机制具有重要影响。甲基化后 DNA 的构象变化允许或禁止转录机制的结合。其他表观遗传因素包括组蛋白修饰和非编码 RNA（如 miRNA），它们也在 OFC 病因学中发挥重要作用。

胚胎极易受到环境因素的影响，例如母亲吸烟、饮酒、不良饮食、过热以及接触药物和污染物。这些环境因素会导致包括 OFC 在内的发育障碍，也可能产生跨代后果。胚胎面部发育不仅容易受到子宫内暴露的影响，而且还受到怀孕前母亲甚至父亲暴露的影响。母体和父体的环境影响可以作为表观遗传标记转移，可以在胚胎中表现为 OFC，而无需在子宫内直接暴露。虽然我们知道其中一些不利的环境因素可以消除，但其他因素是无法避免的。该研究能否通过其他途径（例如使用孕前和产前补充剂）帮助保护我们免受 OFC 的侵害？

博士 Yulai Zhou、Julian Little 以及渥太华大学、邓迪大学和杜克大学的合作者提供了一组荟萃分析，以确定叶酸摄入量/状态的不同指标与 OFC 之间的关系。自 2008 年发布上一次此类分析以来 (Johnson & Little, 2008)，确定了 2007-2020 年发表的 56 篇论文。根据 2008 年的研究，结论是使用含叶酸的补充剂可使唇裂/腭裂 (CL/P) 的风险降低 18%，但腭裂 (CP) 的风险没有显着降低。他们还报告说，摄入多种维生素后，CL/P 风险降低了约 23%。最新的研究结果表明，在围孕期间服用包括叶酸在内的多种维生素补充剂可以预防 CL/P，将风险降低 40%，而仅服用 CP，可以将风险降低 19%。单独补充叶酸似乎没有帮助。此次更新与 2008 年的研究不同，因为研究参与者来自更广泛的国家，扩大了社会经济变异性。这些荟萃分析之间的比较说明了这些类型分析固有的困难以及需要进行更多研究以更清楚地了解预防 OFC 所需的内容。尽管如此，好消息是补充剂似乎可以有效预防某些 OFC。