Alterations in DNA Methylation in Orofacial Clefts

Orofacial clefts are among the most common craniofacial anomalies with multifactorial etiologies, including genetics and environments. DNA methylation, one of the most acknowledged mechanisms of epigenetics, is involved in the development of orofacial clefts. DNA methylation has been examined in patients with non-syndromic cleft lip with cleft palate (nsCL/P) from multiple specimens, including blood, saliva, lip, and palate, as well as experimental studies in mice. The results can be reported in two different trends: hypomethylation and hypermethylation. Both hypomethylation and hypermethylation can potentially increase the risk of nsCL/P depending on the types of specimens and the specific regions on each gene and chromosome. This is the most up-to-date review, intending to summarize evidence of the alterations of DNA methylation in association with the occurrence of orofacial clefts. To make things straightforward to understand, we have systematically categorized the data into four main groups: human blood, human tissues, animal models, and the factors associated with DNA methylation. With this review, we are moving closer to the core of DNA methylation associated with nsCL/P development; we hope this is the initial step to find a genetic tool for early detection and prevention of the occurrence of nsCL/P.

Association of Fetal MTHFR 677C > T Polymorphism with Non-Syndromic Cleft Lip with or without Palate Risk: A Systematic Review and Meta-Analysis

This study was conducted to estimate the precise association of fetal MTHFR 677 C > T polymorphism with risk of nonsyndromic cleft lip with or without cleft palate (NSCL ± P) using a large-scale meta-analysis. Methods: A comprehensive literature search was performed using studies published on PubMed, Science Direct, Scopus and CNKI databases up to November 1, 2019. Results: A total of 38 studies with 6,525 children with NSCL ± P and 8,606 controls were selected. Overall, there was a significant association between MTHFR 677 C > T polymorphism and NSCL ± P risk. Subgroup analysis by ethnicity revealed that MTHFR 677 C > T polymorphism contributed to development of NSCL ± P in Caucasian and Mixed populations, but not in Asians. When stratified by country of origin, we found a significant association in Brazilian, Turkish and Indian populations, but not in Chinese and US-American. Conclusions: This meta-analysis provides strong evidence that fetal MTHFR 677 C > T polymorphism is significantly associated with NSCL ± P risk.

Multigenerational analysis of sex-specific phenotypic differences at midgestation caused by abnormal folate metabolism

The exposure to adverse environmental conditions (e.g. poor nutrition) may lead to increased disease risk in an individual and their descendants. In some cases, the results may be sexually dimorphic. A range of phenotypes has been associated with deficiency in or defective metabolism of the vitamin folate. However, the molecular mechanism linking folate metabolism to development is still not well defined nor is it clear whether phenotypes are sex-specific. The enzyme methionine synthase reductase (MTRR) is required for the progression of folate metabolism and the utilization of methyl groups from the folate cycle. Previously, we showed that the hypomorphic Mtrr^gt mutation in mice results in metabolic disruption, epigenetic instability, and a wide spectrum of developmental phenotypes (e.g. growth defects, congenital malformations) at midgestation that appear in subsequent wild-type generations. This transgenerational effect only occurs through the maternal lineage. Here, we explore whether the phenotypes that result from either intrinsic or ancestral Mtrr deficiency are sexually dimorphic. We found that no sexual dimorphism is apparent in either situation when the phenotypes were broadly or specifically defined. However, when we focused on the group of phenotypically normal conceptuses derived from maternal grandparental Mtrr deficiency, we observed an apparent increase in placental efficiency in each subsequent generation leading to F4 generation female embryos that weigh more than controls. These data suggest that ancestral abnormal folate metabolism may lead to male grandprogeny that are less able to adapt or female grandprogeny that are programmed to become more sensitive to folate availability in subsequent generations.