Correlation between mandibular retrognathia and induction of cleft palate with 6-aminonicotinamide in the rat

Rare variants analyses suggest novel cleft genes in the African population

Non-syndromic orofacial clefts (NSOFCs) are common birth defects with a complex etiology. While over 60 common risk loci have been identified, they explain only a small proportion of the heritability for NSOFCs. Rare variants have been implicated in the missing heritability. Thus, our study aimed to identify genes enriched with nonsynonymous rare coding variants associated with NSOFCs. Our sample included 814 non-syndromic cleft lip with or without palate (NSCL/P), 205 non-syndromic cleft palate only (NSCPO), and 2150 unrelated control children from Nigeria, Ghana, and Ethiopia. We conducted a gene-based analysis separately for each phenotype using three rare-variants collapsing models: (1) protein-altering (PA), (2) missense variants only (MO); and (3) loss of function variants only (LOFO). Subsequently, we utilized relevant transcriptomics data to evaluate associated gene expression and examined their mutation constraint using the gnomeAD database. In total, 13 genes showed suggestive associations (p = E-04). Among them, eight genes (ABCB1, ALKBH8, CENPF, CSAD, EXPH5, PDZD8, SLC16A9, and TTC28) were consistently expressed in relevant mouse and human craniofacial tissues during the formation of the face, and three genes (ABCB1, TTC28, and PDZD8) showed statistically significant mutation constraint. These findings underscore the role of rare variants in identifying candidate genes for NSOFCs.

Rare Variants Analyses Suggest Novel Cleft Genes in the African Population

Non-syndromic orofacial clefts (NSOFCs) are common birth defects with a complex etiology. While over 60 common risk loci have been identified, they explain only a small proportion of the heritability for NSOFC. Rare variants have been implicated in the missing heritability. Thus, our study aimed to identify genes enriched with nonsynonymous rare coding variants associated with NSOFCs. Our sample included 814 non-syndromic cleft lip with or without palate (NSCL/P), 205 non-syndromic cleft palate only (NSCPO), and 2150 unrelated control children from Nigeria, Ghana, and Ethiopia. We conducted a gene-based analysis separately for each phenotype using three rare-variants collapsing models: (1) protein-altering (PA), (2) missense variants only (MO); and (3) loss of function variants only (LOFO). Subsequently, we utilized relevant transcriptomics data to evaluate associated gene expression and examined their mutation constraint using the gnomeAD database. In total, 13 genes showed suggestive associations (p = E-04). Among them, eight genes (ABCB1, ALKBH8, CENPF, CSAD, EXPH5, PDZD8, SLC16A9, and TTC28) were consistently expressed in relevant mouse and human craniofacial tissues during the formation of the face, and three genes (ABCB1, TTC28, and PDZD8) showed statistically significant mutation constraint. These findings underscore the role of rare variants in identifying candidate genes for NSOFCs.

Early Craniofacial Morphology and Growth in Children with Bilateral Complete Cleft Lip and Palate

Purpose

Analysis of craniofacial morphology and growth in children with bilateral complete cleft lip and palate (BCCLP), compared with a control group with unilateral incomplete cleft lip (UICL), before any treatment as well as 20 months after lip closure.

Material

The children were drawn from a group representing all Danish children with cleft born 1976 to 1981. Sixty-four children were included in the study (19 BCCLP and 45 UICL). The ages were 2 and 22 months at examinations 1 and 2, respectively.

Method

The method of investigation was infant cephalometry in three projections. The craniofacial morphology was analyzed using linear, angular, and area variables. Growth was defined as the displacement vector from the coordinate of the corresponding landmark in the x-ray at examination 1 to its coordinate at examination 2, corrected for x-ray magnification. The growth of an anatomical region in a patient was assessed by investigating the growth pattern formed by a collection of individual growth vectors in that region.

Results

The BCCLP group differed significantly from the UICL group. The most striking findings in BCCLP were an extremely protruding premaxilla; markedly increased posterior maxillary width; increased width of the nasal cavity; short maxilla with reduced posterior height; short mandible; bimaxillary retrognathia; severe reduction in the size of the pharyngeal airway; and a more vertical facial growth pattern.

Conclusion

Our findings indicate that a facial type including a wide and posterior short maxilla, short mandible, and bimaxillary retrognathia might be a liability factor that increases the probability of developing cleft lip and palate.

Early Postnatal Development of the Mandible in Children with Isolated Cleft Palate and Children with Nonsyndromic Robin Sequence

Objective

Analysis of early postnatal mandibular size and growth velocity in children with untreated isolated cleft palate (ICP), nonsyndromic Robin sequence (RS), and a control group of children with unilateral incomplete cleft lip (UICL).

Material

114 children (66 isolated cleft palate, 7 Robin sequence, 41 unilateral incomplete cleft lip) drawn from a group representing all Danish cleft children born from 1976 through 1981. All children were examined at both 2 and 22 months of age.

Methods

Cephalometric x-rays and maxillary plaster casts. Mandibular length and height were measured and mandibular growth velocity (mm/year) was calculated. Cleft width was measured on the casts at 2 months of age.

Results

Mean mandibular length and posterior height were significantly smaller in isolated cleft palate and Robin sequence, compared with unilateral incomplete cleft lip. Mandibular length in Robin sequence was also significantly shorter, compared with isolated cleft palate. No significant difference was found between mean mandibular growth velocities in the three groups. No significant correlation was found between mandibular length and cleft width in either isolated cleft palate or Robin sequence at 2 months of age.

Conclusion

The children with isolated cleft palate and Robin sequence had small mandibles shortly after birth, but with a relatively normal growth potential. No true mandibular catch-up growth was found up to 22 months of age in either group. No significant correlation was found between mandibular size and cleft width in either group at 2 months of age. However, there was a significant trend toward the shorter the mandible, the more severe the sagittal extension of the cleft.

Pathogenesis of Cleft Palate in Robin Sequence: Observations From Prenatal Magnetic Resonance Imaging

PURPOSE

The etiology of the palatal cleft in Robin sequence (RS) is unknown. The purpose of this study was to assess the position of the fetal tongue at prenatal magnetic resonance imaging (MRI) and to suggest a potential relation between tongue position and development of the cleft palate seen in most patients with RS.

MATERIALS AND METHODS

This is a retrospective case-and-control study including fetuses with prenatal MRIs performed in the authors' center from 2002 to 2017. Inclusion criteria were 1) prenatal MRI of adequate quality, 2) liveborn infant, and 3) postnatal diagnosis of RS (Robin group) or cleft lip and palate (CLP group). Patients with postnatal RS without a palatal cleft were excluded. A control group with normal facial morphology was matched by gestational age. The outcome variable was tongue position at fetal MRI, described as within the cleft, along the floor of the mouth (normal), other, or indeterminate.

RESULTS

One hundred twenty-two patients with mean gestational age at MRI of 25.8 ± 4.9 weeks were included (Robin, n = 21 [17%]; CLP, n = 47 [39%]; control, n = 54 [44%]). The tongue was visualized within the palatal cleft in 76.2% of the Robin group and 4.3% of the CLP group. The tongue was found along the floor of the mouth (normal) in the remainder of the Robin and CLP groups and in 100% of the control group.

CONCLUSION

These findings suggest a relation between in utero tongue position and the development of cleft palate in RS.

Analysis of the Relationship Between Micrognathia and Cleft Palate: A Systematic Review

Objective To gather data from relevant experimental and observational studies to determine the relationship between micrognathia and cleft palate. The goal is to raise awareness and motivate clinicians to consider the cause and effect relationship when confronted with patients with cleft palate, even if there is no clearly noticeable mandibular abnormality. Design Several electronic databases were systematically examined to find articles for this review, using search terms including "cleft palate," "micrognathia," "tongue," and "airway obstruction." PubMed was the source of all the articles chosen to be included. Exclusion criteria included case reports, articles focused on treatment options, and articles only tangentially related to cleft palate and/or micrognathia. Results A total of 930 articles were screened for relevance, and 82 articles were chosen for further analysis. Evidence gathered in this review includes a variety of etiological factors that are causative or associated with both micrognathia and cleft palate. Observational studies relating the two abnormalities are also included. Much of the included literature recognizes a cause-and-effect relationship between micrognathia and cleft palate. Conclusion On the basis of the published data, we suggest that micrognathia does induce cleft palate in humans and animals. With knowledge of this causative relationship, clinicians should consider the importance of gathering cephalometric data on the mandibles and tongues of patients presenting with isolated cleft palate to determine whether they have micrognathia as well. With more data, patterns may emerge that could give insight into the complex etiology of nonsyndromic cleft palate.

Cleft Palate in a Mouse Model of SOX2 Haploinsufficiency

OBJECTIVE

While SEX-determining region Y-Box 2 (SOX2) mutations are typically recognized as yielding ocular and central nervous system abnormalities, they have also been associated with other craniofacial defects. To elucidate the genesis of the latter, Sox2 hypomorphic (Sox2(HYP)) mice were examined, with particular attention to secondary palatal development.

RESULTS

Clefts of the secondary palate were found to be highly penetrant in Sox2(HYP) mice. The palatal clefting occurred in the absence of mandibular hypoplasia and resulted from delayed or failed shelf elevation.

CONCLUSIONS

Sox2 hypomorphism can result in clefting of the secondary palate, an effect that appears to be independent of mandibular hypoplasia and is thus expected to result from an abnormality that is inherent to the palatal shelves and/or their progenitor tissues. Further clinical attention relative to SOX2 mutations as a basis for secondary palatal clefts appears warranted.

Validation of whole chick embryo cultures, whole rat embryo cultures and aggregating embryonic brain cell cultures using six pairs of coded compounds

A comparative study was performed to assess the effects of six pairs of coded compounds using cultures of whole chick and rat embryos as well as aggregating brain cell cultures. Developed originally for basic studies in developmental biology, these three culture systems have been adapted for the screening of chemicals in the field of prenatal toxicology. Chick and rat embryos were cultured for 2 days during the early stages of organogenesis. Aggregating cell cultures were prepared from early foetal rat telecephalon and grown for 14 days in a chemically defined medium. Concentration-response relationships were established by treating whole embryos in vitro for 2 days, and aggregating brain cell cultures for 9 days. After decoding the compounds, the results showed that, in the three test systems, specific effects were induced at comparable concentration levels. Similar compound-related malformations could be observed in both chick and rat whole embryo cultures. In aggregating brain cell cultures, neuron- and glia-specific effects could be distinguished. Based on the results obtained in the three in vitro systems, the following concentration ranges were determined for the teratogenic/toxic potencies of the test compounds (in mol/litre): <10(-6): retinoids (Ro 13-6307, Ro 1-5488), 6-aminonicotinamide, ketoconazole; 10(-6)-10(-3): 4-hydroxypyridine, sulfadiazine, sulfanilamide, caffeine, theophylline, metronidazole, methoxyacetic acid; >10(-3): methoxyethanol. In general, the three in vitro test systems were found to provide concordant and complementary data on the toxicity and teratogenicity of a given compound. These data were also comparable with those available from in vivo studies. It is therefore concluded that such a test battery could contribute significantly to risk assessment and to the reduction of in vivo experimentation in reproductive toxicology.

Facial Profile Evaluation of Isolated Pierre Robin Sequence

Objective

To evaluate numerically the facial profile of children with isolated Pierre Robin sequence (PRS) and to compare them with a control group that has no pathologies and exhibits regular and balanced facial growth, with no skeletal alterations.

Patients

Eighty-three children aged 5 to 10 years (PRS group, n = 60; control group, n = 23) were selected.

Setting

Hospital for Rehabilitation of Craniofacial Anomalies, University of Sao Paulo (HRAC-USP). Children from the control group were taken from the program of Interceptive Orthodontics at HRAC-USP.

Design

Angular and ratio analyses of the facial profiles in both groups were realized through digital photographs. The PRS group was subdivided into two groups—complete and incomplete—according to the sagittal extension of the cleft palate, to investigate the possible influence of cleft extension on the face.

Results

The facial convexity angle and the facial inferior third angle were considerably higher in the PRS groups than in the control group and were not significantly different between PRS groups. Nasolabial angle did not differ between groups.

Conclusion

The facial profile was more convex in individuals with PRS than in those with regular facial growth and with no pathology. The mandible was responsible for the convexity of the profile in PRS because of its lack off anterior projection. An important relationship between the extension of the cleft palate and alterations in facial profile in PRS was not observed.

Experimental aspects of the pathogenesis of Robin sequence

OBJECTIVE

The Pierre Robin Sequence (PRS) is a good example of disturbed embryonic development of the secondary palate involving insufficient mandibular growth, failed forward tongue movement, and, in the case of a cleft, impeded fusion of the secondary palate. Discussion continues regarding which of the involved pathogenetic factors is the primary cause of the induced cascade of signs: insufficient mandibular growth or failed descent of the tongue.

DESIGN

Forty-five randomly selected, 18-day-old formalin-fixed A/WySn mouse fetuses were investigated. The strain is known to have a basic genetic defect and as much as 44% clefts in the offspring. Twenty-four fetuses in the group had a cleft palate. Mandible position was measured relative to the head and to the presence or absence of a cleft. Cleft width and tongue position were also determined. Thirty-eight NMRI mouse fetuses of the same age served as controls.

RESULTS

All A/WySn fetuses showed marked mandibular retrognathia, which was more severe in the cleft group (p < .05), but there was no correlation between the degree of retrognathia and cleft width. The median cleft width was 3.4 mm (1.6 through 6.3 mm). The tongue was in the cleft in all 12 fetuses with wide clefts (>3.4 mm wide), and free in the oral cavity in the other 12. Tongue position did not influence the degree of retrognathia (p < .05). Moreover, the tongue was free in all fetuses with severe retrognathia.

CONCLUSION

The results support the primary role of retroposition of the mandible in the development of cardinal symptoms of Pierre Robin Sequence.

Reduction of procarbazine-induced cleft palates by prenatal folic acid supplementation in rats

We investigated the effects of prenatal folic acid supplementation on procarbazine (PCZ)-induced intra-uterine growth retardation (IUGR), cleft palates, and microgenia. Three groups of gravid rats were treated with 200 mg/kg body weight (BW) PCZ on day 13.5 of gestation (GD13.5). Two groups of them were additionally supplemented with 1 and 2.5 mg/kg folic acid, respectively, from GD13.5 through GD16.5. On GD19.5, all fetuses were delivered by caesarian sections and sexed subsequently. Numbers of live and dead fetuses as well as resorptions were counted. Data on fetal BW, crown-rump length, tail length, placental weight, and diameter were collected. Fetal heads were histologically scrutinized for the occurrence of cleft palates and microgenia. Folic acid at 2.5 mg/kg diminished PCZ-induced IUGR. In male fetuses, both folic acid doses significantly reduced the incidence of cleft palates and microgenia, while in females, only the high folic acid dose was capable of lowering the occurrence frequency of cleft palates. We conclude that folic acid supplementation at the used doses confers a substantial protection against PCZ-induced IUGR and incidence of cleft palates and microgenia. However, these effects are gender-related and dose-dependent.

Craniofacial morphology and growth comparisons in children with Robin Sequence, isolated cleft palate, and unilateral complete cleft lip and palate

OBJECTIVE

Comparison of early craniofacial morphology and growth in children with nonsyndromic Robin Sequence (RS), isolated cleft palate (ICP), and unilateral complete cleft lip and palate (UCCLP).

SUBJECTS

One hundred eight children with cleft: 7 with RS, 53 with ICP, and 48 with UCCLP were included in the study. The children were drawn from the group of all Danish children with cleft born 1976 through 1981.

METHOD

Three-projection infant cephalometry.

RESULTS

The craniofacial morphology in the RS, ICP, and UCCLP groups had some common characteristics: a wide maxilla with decreased length and posterior height, wide nasal cavity, short mandible, bimaxillary retrognathia, and reduced pharyngeal airway. The shortest mandible was found in RS followed by ICP and UCCLP; the pharyngeal airway was reduced in RS and ICP, compared with UCCLP; and the maxillary complex and nasal cavity were wider in UCCLP than in the other groups. The amount of facial growth in all three groups was similar; however, the direction was more vertical in UCCLP than in RS and ICP.

CONCLUSION

Except for a shorter RS mandible, the facial morphology of infants with RS and ICP was similar, as was the amount of facial growth and the growth pattern. The differences in facial morphology can be ascribed to the difference in the primary anomaly. The amount of facial growth was similar in the three groups; however, the growth pattern showed a more vertical direction in UCCLP than in RS and ICP. It is hypothesized that the mandibular retrognathia in RS represents the outer end of that of the ICP distribution.

Craniofacial comparisons in 22-month-old lip-operated children with unilateral complete cleft lip and palate and unilateral incomplete cleft lip

OBJECTIVE

The objective of the study was to analyze the craniofacial morphology in infants with unilateral complete cleft lip and palate (UCCLP) in which the lip and the anterior part of the palate had been surgically closed at 2 months of age and to compare the morphology with that of a control group with unilateral incomplete cleft lip (UICL) in which the lip had also been surgically closed at 2 months of age.

DESIGN

The sample consisted of a total of 108 cleft children all fulfilling the entry criteria, besides diagnosis, as follows: The child was of Danish origin; the age of the child was between 650 and 750 days (approximately 22 months) at the time of examination; the child was healthy except for its single cleft malformation; the surgical procedure in each group had been performed at about 2 months of age by the same surgeon. The surgical methods used were a Tennison procedure (UICL group) and a Tennison procedure supplemented by palatovomer plasty (UCCLP group).

METHODS

The method of investigation was infant cephalometry in the lateral, frontal, and axial projections. Linear, angular, and area variables describing the craniofacial morphology were calculated and supplemented by mean plots from the cephalometric projections in the two groups.

RESULTS AND CONCLUSIONS

Statistical analysis based on Student's t test showed that the facial morphology in the 22-month-old UCCLP group differed significantly from that of the UICL group. The most pronounced differences were found in the maxillary complex and the mandible. The deviations observed in the UCCLP group at 22 months of age were similar to those previously observed at 2 months of age. However, several of the dysmorphic traits had become less pronounced; some had remained the same; and a few had become worse with time.

The fetal cleft palate: I. Characterization of a congenital model

Any animal model of a human congenital anomaly established by iatrogenic methods involving intrauterine fetal manipulation has limited clinical applicability. A congenital model that more closely simulates the etiopathogenesis of a human anomaly may provide data that can more readily be extrapolated to that anomaly and, therefore, be used in diagnostic and management strategies. The present work provides a description and characterization of a congenital model of cleft palate in the goat. Palatal shelf closure normally occurs at approximately day 38 of gestation in the caprine species. Sixteen pregnant goats were gavaged twice daily during gestational days 32 through 41 [term, 145 days] with a plant slurry of Nicotiana glauca containing the piperidine alkaloid teratogen anabasine. Gross analysis and measurement of fetal clefts were performed at 60, 70, and 85 days gestation (four fetuses were studied at each time point). Seventeen clefted kids were sacrificed at specific intervals after birth (2 weeks, and 1, 3, and 6 months); after skull debridement and preparation, they were compared with 12 unclefted control kids. Complete clefting of the secondary palate occurred in 97 percent of the fetuses. In all cases, the cleft extended from the posterior aspect of the alveolar ridge to the uvula; the majority of these clefts were bilateral, with complete detachment of the vomer. Morphologically, these clefts were similar to human clefts. Eighteen percent of clefted newborn kids demonstrated gross maxillary hypoplasia and midfacial retrusion at birth with a relative Class III malocclusion. Direct measurement of the congenital caprine skulls confirmed these findings. The incidence of midfacial growth abnormalities in these clefted animals raises questions regarding the etiopathogenesis of facial dysmorphology that is unrelated to scarring of the maxilla. This congenital cleft palate model is currently being used to explore these questions and others related to craniofacial growth and palatal function after in utero repair.

Effects of vitamin B6 on beta-aminoproprionitrile-induced palatal cleft formation in the rat

OBJECTIVE

This study was conducted to evaluate the effects of beta-aminoproprionitrile and vitamin B6 on palatal clefting.

METHOD

In four groups of pregnant Sprague-Dawley rats, beta-aminoproprionitrile (BAPN; 600 mg/kg b.w.) was given by gavage on embryonal day 15, 7 hours to induce palatal clefts. Vitamin B6 (10 mg/kg b.w., IM) was given twice on embryonal day 14, 7 hours and on day 15, 7 hours. The possibility that the food's content of vitamin B6 affected the results was also tested. Palatal cleft formation was divided into four different grades, ranging from no cleft formation to total cleft formation.

RESULTS/CONCLUSION

It was found that BAPN induces cleft palate in rat fetuses and that this defect can be prevented both in number and severity by administration of vitamin B6 before and simultaneously with BAPN.

The role of retinoids in normal and abnormal embryonic craniofacial morphogenesis

The objective of this article is to evaluate the role of retinoids in the developing head and face. This article covers two lines of evidence that strongly support a role for retinoids in craniofacial development. First, the specific effects of exogenous retinoids on the head and face are covered and mechanisms for the specificity discussed. Second, the function of endogenous retinoids in facial development is discussed in relation to the distribution of retinoid-binding substances in the face. Finally, the interaction of retinoids with other genes known to be expressed in the face as well as other factors required for facial growth is discussed.

Craniofacial dysmorphogenesis following hypervitaminosis A in mice

Malformations of the temporomandibular joint (TMJ), zygomatic arch, middle ear ossicles, and mandibular musculature following hypervitaminosis A were described in fetal mice. Pregnant mice (Mus musculus) were each given a 0.2-ml solution of corn oil containing 10,000 IU of retinol palmitate by gavage on day 8.7. Thirty-eight fetal heads were collected and hemisected. The left hemiheads were serially sectioned, stained, and examined histologically. Right halves were cleared and double-stained with alizarin red and alcian blue. The craniofacial morphologies of the test mice were found to vary from normal to maximally involved (feature unidentifiable) even among littermates. Both inter- and intralitter variation were discussed. Errors in chondrogenesis were determined to have produced the variety of dysmorphologies observed. Changes in Meckel's cartilage affected both the TMJ and ossicles; the presence of ectopic cartilages affected the zygomatic arch; and the musculature was affected secondary to skeletal system changes. Several modes of vitamin A interference leading to craniofacial dysmorphogenesis have been proposed in the literature. It was determined that proposals implicating altered cellular differentiation were the most compatible with the in vivo data recorded here and elsewhere.

Measuring histological form change with finite element methods: an application using diazo-oxo-norleucine (DON)-treated rats

Analyses of drug-induced anatomical malformations routinely rely on linear measurements as a data base. Morphometric approaches utilizing these measures become inappropriate at the histological level at which a constant external referencing system is impossible to achieve. The purpose of this study was to quantify anatomical form change in the craniofacial region of late embryonic rats induced by a known teratogen, diazo-oxo-norleucine (DON), independent of any global referencing system. A sample of 17 untreated specimens of 17-day gestation served as the control. A second group, equivalent in number and age, received 2.0 mg DON on day 15. Homologous landmarks were identified in each specimen and craniofacial regions were partitioned with respect to these bounding nodes into nasal, oral, and mandibular elements. Form change was viewed as the continuous deformation of a reference craniofacial region from a 15-day untreated specimen into each final 17-day geometry. An interactive graphics program generated spatially invariant measures of form change through finite element methods. A local coordinate system was established for each element. A point within each region of the 15-day reference specimen was selected and the spatial relationship between this point and bounding nodes was quantified through interpolation functions. Size and shape variables were derived from a Lagrangian strain tensor, and values were compared between groups. Results showed that all three craniofacial regions were smaller in size among DON-treated specimens, but only oral and mandibular region shapes were different from controls. The finite element approach was considered superior to other histological morphometric techniques since an entire geometry was described and a visual description of form change as well as spatially invariant measures of size and shape change were derived.

Development of human craniofacial morphology during the late embryonic and early fetal periods

After formation of the primary palate during the fifth and sixth weeks postconception (PC), human facial morphology develops rapidly and by 10 weeks PC the face has a typically human appearance. The objective of this study was to review major growth changes associated with development of face shape during this period. Morphometric evaluation of staged human embryos and fetuses in the Carnegie Embryological Collection showed that between 7 and 10 weeks PC when crown-rump (CR) length increased from 18 to 49 mm, facial structures grew predominantly in the sagittal plane, with a four-fold increase in length, a two-fold increase in height, but little change in width. These growth changes altered relations of oronasal structures and at 8 weeks PC the palatal shelves elevated. The sagittal position of the maxilla and the mandible to the anterior cranial base increased by 25 degrees and 30 degrees, respectively, and the mandible was prognathic during secondary palate closure in the first 2 weeks of fetal development. Both the mean cranial base angulation--which remained unchanged at 128 degrees--and the achieved maxillary position of 84 degrees were similar to the angulations present later, prenatally and postnatally. Therefore, human patterns of cranial base angulation and maxillary position appear to develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the continuous craniofacial skeleton. The results suggest that rapid directional growth of the primary cartilages is important to development of normal human facial morphology and that interference with normal growth changes during this early critical period may produce irreversible effects on the face.

Prenatal repair of experimentally induced clefts in the secondary palate of the rat

A refined technique of amniotic sac puncturing at day 16.2 (i.e., 16 + 2/10 days) of gestation was employed in order to produce a series of total clefts and rare forms of partial clefts in Sprague-Dawley rat fetuses. From a total of 410 fetuses of a precise, individually determined age, 95 upper jaws were examined in the scanning electron microscope and, in part, in serial Epon sections. All fetal heads were examined macroscopically. Total clefts were found in 48.9% of a total of 184 viable rat fetuses examined at day 17.8 of smear age and in 21.8% of a total of 211 fetuses examined at day 19.3. Partial clefts were observed in 14.1% and 18.5% of fetuses at days 17.8 and 19.3 of smear age, respectively. At day 19.3, 16.1% of the viable fetuses showed a very inconspicuous, small abnormality (with residual clefting and incomplete fusion with the nasal septum) in the region of the palatine foraminae. Morphological observations suggested that under conditions of detained palatal closure (1) fusion of the soft palatal shelves commences independently from and prior to fusion of the hard palate, (2) delayed palatal shelf fusion proceeding in the anterior direction may occur with or without remaining sickle-shaped clefts in the anterior hard palate, and (3) in fetuses with small sickle-shaped clefts, fusion of the palatal shelves with the nasal septum does not occur. The present data imply that an almost total prenatal repair and delayed closure of the secondary palate may occur in rats that, at day 16.2 of multiple analysis age, most certainly had a total palatal cleft resulting from tongue resistance.

Abnormal head posture associated with induction of cleft palate by methylmercury in C57BL/6J mice

Maternal treatment with methylmercury (MeHg) has been shown to induce a high frequency of cleft palate and produce growth retardation in rat and mouse fetuses, but the relation between these effects is unknown. The objective of this study was to determine if mandibular growth retardation was a factor that contributed to induction of cleft palate in C57BL/6J mice. Two doses of MeHg (10 mg/kg maternal body weight) were given subcutaneously on days 10 and 11 of gestation, and the fetuses were morphometrically studied on days 14, 15, and 18. Full clefts of the secondary palate were present in approximately half of the treated day 15 and 18 fetuses; therefore, the cleft palate (CP) and noncleft palate (NCP) groups were analyzed separately to facilitate identification of morphologic changes associated with the clefting. The results showed that, compared with controls, the day 14 MeHg-treated fetuses had significantly smaller placental weights, but only half of the fetuses had delayed palatal shelf elevation, reduced body weight, and delayed morphological development. However on day 15, the CP and the NCP groups had similar reductions in body weight and placental weight. A striking downward and forward positioning of the head was present in the MeHg-treated fetuses with the CP group more severely affected than the NCP group. Significant differences between the three groups (control, NCP, and CP) were present with mean head-to-body angles of 67 degrees, 60 degrees and 51 degrees, respectively. The absence of normal head lifting resulted in a relative mandibular retrognathia that when combined with a decrease in mandibular length produced alterations in spatial relations that were most severe in the CP fetuses. The results suggest that after exposure to MeHg, palatal closure is affected by altered tongue posture associated with the abnormal head positioning and shortening of the mandible that develop following placental and embryonic growth retardation.

A morphometric analysis of craniofacial growth and changes in spatial relations during secondary palatal development in human embryos and fetuses

Staged human embryos and fetuses in the Carnegie Embryological Collection were morphometrically analyzed to show craniofacial dimensions and changes in spatial relations, and to identify patterns that would reflect normal developmental events during palatal formation. Normal embryos aged 7-8 weeks postconception (Streeter-O'Rahilly stages 19-23) and fetuses aged 9-10 weeks postconception, in eight groups with mean crown-rump (CR) lengths of 18-49 mm, were studied with cephalometric methods developed for histologic sections. In the 4-week period studied, facial dimensions increased predominantly in the sagittal plane with extensive changes in length (depth) and height, but limited changes in width. Growth of the mandible was more rapid than the nasomaxillary complex, and the length of Meckel's cartilage exceeded the length of the oronasal cavity at the time of horizontal movement of the shelves during stage 23. Simultaneously with shelf elevation, the upper craniofacial complex lifted, and the tongue and Meckel's cartilage extended forward beneath the primary palate. Analysis of spatial relations in the oronasal cavity showed that the palatomaxillary processes became separated from the tongue--mandibular complex as the head extended, and the tongue became positioned forward with growth of Meckel's cartilage. As the head position extended by 35 degrees, the cranial base angulation was unchanged and the primary palate maintained a 90 degrees position to the posterior cranial base. However, the sagittal position of the maxilla relative to the anterior cranial base increased by 20 degrees between stages 19 and 23. In the late embryonic and early fetal periods, the mean cranial base angulation of approximately 128 degrees and the mean maxillary position angulation of approximately 84 degrees were similar to the angulations previously shown to be present later prenatally and post-natally. The results suggest that human patterns of cranial base angulation and maxillary position to the cranial base develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the primary skeleton.

Correlation between alterations in Meckel's cartilage and induction of cleft palate with beta-aminoproprionitrile in the rat

The lathyrogen beta-aminoproprionitrile (BAPN) induces cleft palate in rats when administered at a critical time in secondary palate formation. BAPN is known to inhibit the crosslinking of newly synthesized collagen, but its primary site of action in producing cleft palate is unknown. In this study time-mated Sprague-Dawley rats were given a single oral dose of 600 mg/kg BAPN at five known gestational ages in the 48 hours before palatal shelf elevation, and the fetuses were studied on days 16, 17 and 18. Evaluation of craniofacial relations and palate development in BAPN-treated heads revealed that delayed palatal shelf elevation and resulting cleft palate were related to retrognathia of the mandible. However, shortening of the mandible was due primarily to vertical and lateral bending of Meckel's cartilage. High and retruded tongue positions that were present with the deformities in Meckel's cartilage interfered with palatal shelf movement to the horizontal plane. The group treated with BAPN at 15 days 7 hours, approximately 24 hours before normal palatal shelf elevation, had the most severe defects in Meckel's cartilage, the longest delay in palatal shelf elevation and the highest incidence of cleft palate. Inhibition of crosslinking of collagen in Meckel's cartilage appeared to weaken the cartilage during the critical period in facial development when extention of the tongue and mandible beneath the primary palate is required to facilitate palatal shelf elevation.

Differential changes in cartilage cell proliferation and cell density in the rat craniofacial complex during secondary palate development

During mammalian secondary palate formation sagittal growth of the lower face has been shown to be more rapid than that of the upper face, and the tongue and mandible extend beneath the primary palate. In order to identify factors contributing to this differential growth pattern, cellular and morphologic growth of the major cartilages of the upper and lower facial regions were studied in radioautographic sections labeled with tritiated thymidine. Evaluation of cell-density recordings, labeling indices, and structural dimensions revealed significant differences between Meckel's cartilage in the lower face, and the nasal cartilage and anterior cranial base cartilage in the upper face. After formation of the precartilaginous blastema, labeling indices were high in Meckel's cartilage (20-30%), but very low in the nasal cartilage and the anterior cranial base (0-2%). During secondary palate formation the volume of Meckel's cartilage increased more rapidly than the other cartilages and its growth was primarily in the sagittal direction. Between days 15 and 17, the increase in the length of Meckel's cartilage (165%) was approximately twice as great as the increase in the combined length of the nasal cartilage and the anterior cranial base (77%). During this period induction of cleft palate with some teratogens has been shown to severely retard growth of Meckel's cartilage and produce mandibular retrognathia that contributes to delayed elevation of the palatal shelves. Therefore, extensive cell proliferation in Meckel's cartilage, during a period of limited proliferation in other craniofacial cartilages, appears to contribute to its rapid growth and its differential sensitivity to growth inhibition.

Selective inhibition of mandibular growth and induction of cleft palate by diazo-oxo-norleucine (DON) in the rat

A high percentage of cleft palates can be induced in rat fetuses by a single injection of the glutamine analog diazo-oxo-norleucine (DON) on day 15 of gestation. The purpose of this study was to evaluate the effects of DON in vivo on craniofacial growth and spatial relations in order to identify factors that may contribute to the palatal defects. Sprague-Dawley rats in the experimental groups were given a single IP injection of 2.0 mg DON (6 mg/kg maternal body weight) on day 15 and were killed on day 16 or 17. Control fetuses were collected on days 15, 16 and 17. Fetal heads were fixed in Bouin's solution, embedded in Paraplast and serially-sectioned. Midsagittal and coronal sections were projected at 30 X and a series of linear and angular measurements were made. DON had limited effect on growth of the cranial base, nasomaxillary complex, and palatine processes, but dramatically reduced the length of Meckel's cartilage. Treatment with DON delayed shelf elevation approximately 24 hours, and tongue position remained high in the oronasal cavity. Growth retardation in Meckel's cartilage therefore may contribute to delayed shelf movement by retarding downward and forward positioning of the tongue-mandibular complex.