Sex distribution is a factor in teratogenically induced clefts and in the anti-teratogenic effect of thiamine in mice, but not in genetically determined cleft appearance

MicroRNAs and Gene Regulatory Networks Related to Cleft Lip and Palate

Cleft lip and palate is one of the most common congenital birth defects and has a complex etiology. Either genetic or environmental factors, or both, are involved at various degrees, and the type and severity of clefts vary. One of the longstanding questions is how environmental factors lead to craniofacial developmental anomalies. Recent studies highlight non-coding RNAs as potential epigenetic regulators in cleft lip and palate. In this review, we will discuss microRNAs, a type of small non-coding RNAs that can simultaneously regulate expression of many downstream target genes, as a causative mechanism of cleft lip and palate in humans and mice.

New molecular aspects in the mechanism of oromaxillofacial cleft prevention by B-vitamins

Clinical and experimental studies show a clear positive effect of B-vitamins in the prevention of oromaxillofacial clefts, especially cleft lip and palate (CL/P). Hereby the local effect of thiamin (B1) in the amniotic fluid is very important for the embryonic facial development as seen in palatal organ models stimulated by topical B-vitamin application (Scheller et al., 2013a). Moreover a low B1 concentration in the serum and amniotic fluid was found in pregnant mice with clefts in their offspring (Scheller et al., 2013b). Immunochemical analyses of midface sections (ThTr-1 transporter) and the placenta (ThTr-2 transporter) of cleft fetuses with orofacial clefts showed an atypical cytoplasmatic localization (Scheller et al., 2017). mRNA nalyses of different B-vitamin transporters (B1, B2, B5, B7, B9) were performed and showed ThTr2 transporter in a short splice variant in all cleft fetuses. This splice variant may cause a functional loss of the transport capacity through the placenta barrier and result in a low amniotic fluid concentration of vitamin B1. All other analyzed transport proteins showed no functional change. These findings confirm the hypothesis that cleft prevention by high vitamin B1 substitution fails in genetically determined cleft mice, caused by an insufficient B1 uptake and missing local effect.

Proportion of Orofacial Clefts Attributable to Recognized Risk Factors

OBJECTIVE

Estimate the population attributable fraction (PAF) for a set of recognized risk factors for orofacial clefts.

DESIGN

We used data from the National Birth Defects Prevention Study. For recognized risk factors for which data were available, we estimated crude population attributable fractions (cPAFs) to account for potential confounding, average-adjusted population attributable fractions (aaPAFs). We assessed 11 modifiable and 3 nonmodifiable parental/maternal risk factors. The aaPAF for individual risk factors and the total aaPAF for the set of risk factors were calculated using a method described by Eide and Geffler.

SETTING

Population-based case-control study in 10 US states.

PARTICIPANTS

Two thousand seven hundred seventy-nine cases with isolated cleft lip with or without cleft palate (CL±P), 1310 cases with isolated cleft palate (CP), and 11 692 controls with estimated dates of delivery between October 1, 1997, and December 31, 2011.

MAIN OUTCOME MEASURES

Crude population attributable fraction and aaPAF.

RESULTS

The proportion of CL±P and CP cases attributable to the full set of examined risk factors was 50% and 43%, respectively. The modifiable factor with the largest aaPAF was smoking during the month before pregnancy or the first month of pregnancy (4.0% for CL±P and 3.4% for CP). Among nonmodifiable factors, the factor with the largest aaPAF for CL±P was male sex (27%) and for CP it was female sex (16%).

CONCLUSIONS

Our results may inform research and prevention efforts. A large proportion of orofacial cleft risk is attributable to nonmodifiable factors; it is important to better understand the mechanisms involved for these factors.

Oral vitamin B1-substitution does not decrease genetically determined cleft rate in mice (A/WySn)

PURPOSE

Cleft lip and palate (CL/P) are one of the most common human birth defects. Animal experiments and clinical investigations show a clear reduction of teratogenic clefts by a high-dose vitamin B supplementation during early pregnancy, especially in families at risk (reduction of recurrence). The aim of this work was to examine the influence of thiamine (vitamin B1) on CL/P appearance in genetically determined A/WySn mice within different supplementation starting points.

MATERIALS AND METHODS

A total of 24 A/WySn female mice were orally supplemented with high doses (80 mg/kg) of thiamine at different times of pregnancy (5 groups, n = 90). The influence of thiamine on the abortion rate and CL/P appearance in the offspring was analyzed with respect to the concentration of thiamine in the serum and amniotic fluid (HPLC-chromatography). Immunochemical analyses of the ThTr-1 und ThTr-2 receptor-status were performed in midface sections of A/WySn-fetuses and the corresponding placenta, with and without CL/P.

RESULTS

High doses of orally supplemented thiamine did not reduce the CL/P appearance in A/WySn mice. However, the different starting points of vitamin B1 substitution had some influence. Additionally, an obvious decrease in aborted fetuses was noticed in all supplemented groups. The oral substitution caused a clear increase of the serum concentration in all mothers, but showed no increase of the amniotic fluid concentration. Then immunohistochemistry detected an overexpression of ThTr-1 in the midface and an irregular localization of ThTr-2 in the placenta of fetuses with clefts.

CONCLUSION

Our results suggest a time-dependent influence of thiamine on CL/P appearance in female mice. The prophylactic/periconceptional, but not the therapeutic supplementation, starting point can be proposed as a crucial step for regular facial and palatal fusion in embryonic development. The absolute rate of CL/P was not reduced, and the concentration of the water-soluble thiamine could not increase in the amniotic fluid. Thus the proposed local effect of thiamine failed in the development of genetically determined mice.