Masticatory muscle defects in hemifacial microsomia: a new embryological concept.

First arch syndromes correspond to a wide spectrum of human latero-facial congenital anomalies affecting cranial neural crest cells (CNCCs) derivatives of the first pharyngeal arch (PA1). The abnormal traits display variable quantitative expression and are often unilateral. Mandibular skeletal defects are invariably accompanied by hypoplasia or agenesis of masticatory muscles, but no explanation has been proposed for this association. Indeed, during embryonic development, CNCCs give only rise to skeletal components of the head while muscles derive from cephalic myogenic mesodermal cells (CMMCs). Recent studies on animal models have shown that communication between CNCCs and CMMCs is essential for the development of masticatory muscles: genetic lesions affecting only CNCCs can prevent muscularization of the jaws. To evaluate the involvement of CNCC/CMMC interactions in human craniofacial development, we performed a quantitative analysis of masticatory muscle and mandibular bone volumes on craniofacial CT-scans from 8 children, ages 3 months to 16 years, affected by hemifacial microsomia. We found that: (1) in seven patients the masseter muscle is absent in the affected side; (2) the absence of masseter is correlated neither with the age of the patients nor with the volume and shape of the affected ramus; and (3) in all cases the pterygoid and the temporal muscles are either reduced or absent. Our findings suggest that an early developmental event is the origin of the muscular defects in these patients. We propose that the hypoplasia or agenesis of masticatory muscles derives from a defect in the CNCCs/CMMCs communication during early embryonic development.

Intersections of epigenetics, twinning and developmental asymmetries: insights into monogenic and complex diseases and a role for 3D facial analysis.

For decades the relationships of twinning and alterations in body patterning, such as laterality and asymmetry, have been investigated. However, the tools to define and quantify these relationships have been limited and the majority of these studies have relied on associations with subjectively defined phenotypes. The emerging technologies of 3-dimensional (3D) facial scanning and geometric morphometrics are providing the means to establish objective criteria, including measures of asymmetry, which can be used for phenotypic classification and investigations. Additionally, advances in molecular epigenetics provide new opportunities for novel investigations of mechanisms central to early developmental processes, twinning and related phenotypes. We review the evidence for overlapping etiologies of twinning, asymmetry and selected monogenic and complex diseases, and we suggest that the combination of epigenetic investigations with detailed and objective phenotyping, utilizing 3D facial analysis tools, can reveal insights into the genesis of these phenomena.

Proliferating cells in suborbital tissue drive eye migration in flatfish.

The left/right asymmetry of adult flatfishes (Pleuronectiformes) is remarkable given the external body symmetry of the larval fish. The best-known change is the migration of their eyes: one eye migrates from one side to the other. Two extinct primitive pleuronectiformes with incomplete orbital migration have again attracted public attention to the mechanism of eye migration, a subject of speculation and research for over a century. Cranial asymmetry is currently believed to be responsible for eye migration. Contrary to that hypothesis, we show here that the initial migration of the eye is caused by cell proliferation in the suborbital tissue of the blind side and that the twist of frontal bone is dependent on eye migration. The inhibition of cell proliferation in the suborbital area of the blind side by microinjected colchicine was able to prevent eye migration and, thereafter, cranial asymmetry in juvenile Solea senegalensis (right sideness, Soleidae), Cynoglossus semilaevis (left sideness, Cynoglossidae), and Paralichthys olivaceus (left sideness, Paralichthyidae) with a bottom-dwelling lifestyle. Our results correct the current misunderstanding that eye migration is driven by the cranial asymmetry and simplify the explanation for broken left/right eye-symmetry. Our findings should help to focus the search on eye migration-related genes associated with cell proliferation. Finally, a novel model is proposed in this research which provides a reasonable explanation for differences in the migrating eye between, and sometimes within, different species of flatfish and which should aid in our overall understanding of eye migration in the ontogenesis and evolution of Pleuronectiformes.

Sulfotransferase Ndst1 is needed for mandibular and TMJ development.

Heparan sulfate proteoglycans (HS-PGs) regulate several developmental processes, but their possible roles in mandibular and TMJ formation are largely unclear. To uncover such roles, we generated mice lacking Golgi-associated N-sulfotransferase 1 (Ndst1) that catalyzes sulfation of HS-PG glycosaminoglycan chains. Ndst1-null mouse embryos exhibited different degrees of phenotypic penetrance. Severely affected mutants lacked the temporomandibular joint and condyle, but had a mandibular remnant that displayed abnormal tooth germs, substandard angiogenesis, and enhanced apoptosis. In mildly affected mutants, the condylar growth plate was dysfunctional and exhibited thicker superficial and polymorphic cell zones, a much wider distribution of Indian hedgehog signaling activity, and ectopic ossification along its lateral border. Interestingly, mildly affected mutants also exhibited facial asymmetry resembling that seen in individuals with hemifacial microsomia. Our findings indicate that Ndst1-dependent HS sulfation is critical for mandibular and TMJ development and allows HS-PGs to exert their roles via regulation of Ihh signaling topography and action.

Hemifacial microsomia: from gestation to childhood.

Hemifacial microsomia (HFM) is a variable, complex malformation involving asymmetric hypoplasia of the face and ear. Little is known about the risk factors for or consequences of HFM. In this study, we describe 3 studies that have been or are currently being conducted to further our understanding of this malformation. The first completed study examined whether HFM risk is related to maternal exposures that may affect blood flow. In that case-control study, interview data from 230 mothers of children in the case group and 678 mothers of children in the control group suggested that maternal use of vasoactive medications in the first trimester, particularly in combination with cigarette smoking, was associated with increased risks of HFM. The second study is currently underway, in which we are evaluating whether HFM risk is related to genetic variation in pathways associated with vasculogenesis and hemostasis, using DNA collected in the first study. The third ongoing study observes children with HFM to identify psychosocial, cognitive, dental, and medical sequelae. When the children from the original case-control study are 6 or 7 years of age, mothers and teachers complete self-administered questionnaires that cover a wide range of psychosocial development domains. Preliminary analyses of 115 case and 314 control children suggest that children with HFM may have worse teacher-reported academic performance and possibly higher levels of internalizing behavior problems than control children. When data on the full study sample are available, further analyses will determine whether the preliminary findings remain and if they vary by HFM phenotype, parenting style, or indicators of social risk.

Review of the etiologic heterogeneity of the oculo-auriculo-vertebral spectrum (Hemifacial Microsomia).

Hemifacial microsomia is a congenital asymmetry of the lower face that may be associated with other cranial and extracranial anomalies. The variability of its severity, and wide range of anomalies that have been reported with it in some cases has resulted in these composite manifestations being given a number of names, including oculo-auriculo-vertebral spectrum (OAVS). Etiology is often stated to be a perturbation of embryonic blood flow in the developing region, although other factors may also play a role in some cases. Depending on what is considered to be minimum criteria for affected classification, what is often to be presumed to be a sporadic event in a family may be the more severe manifestation of a familial condition. Etiological factors are clearly heterogeneous, the investigation of which is confounded by not only the lack of a refined affected phenotype, but also the apparent influence of genetic factors in some instances that directly influence phenotype perhaps through alteration of mesodermal development, or indirectly through increased susceptibility to vascular disruption. Future studies likely to advance knowledge in this area will need to incorporate an analysis of who may be minimally affected in families, so that advances in genotyping will have greater power to distinguish genetic factors that may influence OVAS through interaction with environmental factors in particular families. The same genetic-environmental factors and or etiological mechanisms may then be investigated in apparently sporadic cases.

Twisted story of eye migration in flatfish.

Early molecular markers for flatfish metamorphosis and eye migration must be linked to the ethmoid region, the earliest part of the flatfish cranium to change, as well as chondral and dermal ossification processes. Serial sections, morphological landmarks, and stereology were used to determine where and when the remodeling of tissues and asymmetry occurs in the head region of metamorphosing Atlantic halibut, Hippoglossus hippoglossus. Not all parts of the head remodel or migrate, and those that do may be asynchronous. Normal metamorphosis limits the torsion of the Atlantic halibut head to the anterior part of the neurocranium and excludes the tip of the snout and the general jaw area. The first cranial structure displaying eye migration-related asymmetric development is the paraethmoid part of the ethmoid cartilage. In early eye migration the medial frontal process moves apace with the eyes, whereas near completion the migrating eye moves significantly closer to the frontal process. Structures of the jaw remain mostly symmetrical, with the exception of the adductor mandibulae muscle and the bone maxillare, which are larger on the abocular than on the ocular side, the muscle occupying the space vacated by the migration of the eye. Thus, normal eye migration involves a series of temperospatially linked events. In juveniles lacking eye migration (arrested metamorphosis), the dermal bone, the prefrontal, does not develop. The two abnormal paraethmoids develop symmetrically as two plate-like structures curving anteriorly, whereas normal elongate fused paraethmoids curve at their posterior. The abocular side retrorbital vesicles are largest in volume only after the completion of normal eye migration. Factors involved in completion of normal metamorphosis and eye migration in flatfish affect chondral and dermal ossification signals in the ethmoid group, as well as remodeling of the mineralized frontal, a series of linked events not involving the entire neurocranium.

Facio-auriculo-vertebral sequence in association with DiGeorge sequence, Rokitansky sequence, and Dandy-Walker malformation: case report.

Extreme variability of expression is characteristic of the facio-auriculo-vertebral sequence. Sporadic and familial cases have been reported with obvious etiologic heterogeneity. Most reports in the literature are of clinical cases. The purpose of this paper is to present a fetal autopsy case report of the facio-auriculo-vertebral sequence in association with DiGeorge sequence, Rokitansky sequence, and Dandy-Walker malformation. A standard neonatal autopsy was performed on a macerated female fetus, gestational age 29 wk. External examination of the fetus revealed hypoplastic right face, low-set microtic right ear, and macrostomia. Internal examination showed hypoplastic thymus and lungs, a type I truncus arteriosus, and ventricular septal defect. Both kidneys showed evidence of pelvi-ureteric junction obstruction. The ovaries and fallopian tubes were present with an absent uterus and vagina (Rokitansky sequence). In addition, Dandy-Walker malformation was identified. Microscopically, a single hypoplastic parathyroid gland was noted and there was cystic renal dysplasia. We report the sixth case of the facio-auriculo-vertebral sequence in association with Rokitansky sequence and the first case of this sequence in association with Dandy-Walker malformation. In addition, features of DiGeorge sequence were present.

Craniofacial asymmetry in development: an anatomical study.

The purpose of this study was to evaluate the occurrence of craniofacial asymmetries in four areas of human skulls of various age groups to test the hypothesis that there is craniofacial symmetry before the chewing habit is established. The data were obtained from 95 skulls of fetuses, infants, children, and adults, from the collection of Federal University of São Paulo. The following measurements were taken on each skull with a digital caliper: from the infraorbital foramen to the anterior nasal spine (IOF); from the greater palatine foramen to the posterior nasal spine (GPF); from the spinous foramen to the basion (SF); and from the spinous foramen to the zygomatic arch (ZA). On different occasions, each measurement was taken three times on both sides of the skull in random order. The mean of the right-side measurements were subtracted from the mean of the left-side measurements, and the differences were transformed into percentages. Comparisons were made by analysis of variance. The presence of cranial asymmetry was statistically significant throughout the whole sample. The minimum value found was 2.8% and the maximum 6.5%. All age groups presented the same degree of asymmetry of distances IOF, GPF, and SF. The group of infants presented a higher degree of asymmetry on distance ZA, followed by the groups of fetuses, children, and adults. This study confirmed statistically significant craniofacial asymmetry in fetuses and infants (before dentition). Therefore, the hypothesis that craniofacial asymmetry only appears after establishment of the chewing habit was not supported.

Fine structure of soft and hard tissues involved in eye migration in metamorphosing Japanese flounder (Paralichthys olivaceus).

The body of a Japanese flounder (Paralichthys olivaceus) changes from a symmetrical to an asymmetrical form during metamorphosis. To obtain detailed information on the mechanisms of the migration of the right eye to the left side, soft and hard tissues in the head of larval flounders were examined using transmission electron microscopy (TEM). Retrorbital vesicles (Rvs) are pairs of sac-like structures under the eyes. It has been suggested that the asymmetrical development of Rvs, with the right (blind) one being bigger than the left, is the driving force behind eye migration. The present study revealed that the ultrastructure of the Rv sheath is quite similar to that of a lymphatic capillary. Thus, it is possible that the Rv is a part of the lymph system, and is probably related to the secondary vascular system in teleosts. If we assume that the Rv sheath has a high permeability to liquid, similar to lymphatic capillaries, it is not plausible that the active expansion of the Rv pushes the eyeball. On the other hand, the pseudomesial bar (Pb) is a bone that is unique to flounders and is present only on the right (blind) side. At the beginning of eye migration, an aggregation of fibroblast-like cells is observed in the dermis under the right eye, where the Pb will subsequently be formed. These cells have a well-developed rough endoplasmic reticulum (rER) and mitochondria, and are probably responsible for formation of the thick layers of collagen fibrils around them. Since it is unlikely that the active expansion of the Rv causes eye migration, the role played by the Pb and its rudiment becomes more significant in right eye migration in the Japanese flounder becomes more significant.

Prenatal diagnosis of atelosteogenesis type I at 21 weeks' gestation.

We describe prenatal diagnosis in a male fetus at 21 weeks of gestation with atelosteogenesis type I (AO I). Fetal ultrasonography (US) revealed absent or deficient ossification of the posterior neural arches of the thoracic spine, humeri, radii, ulnae, fibulae, and short tubular bones other than the distal phalanges, in addition to extremely short, thick femora. Fetal magnetic resonance imaging (MRI) using an ultrafast imaging sequence depicted dysmorphic features, pulmonary hypoplasia, and large cisterna magna. Postmortem radiographs warranted a diagnosis of AO I. Autopsy corroborated not only pulmonary hypoplasia but also laryngeal stenosis. The chondro-osseous histological findings were consistent with those of AO I. Meticulous evaluation using fetal US and MRI permits a definitive prenatal diagnosis of AO I to be made.

Deciduous tooth crown size and asymmetry in strabismic children.

OBJECTIVES: To explore deciduous tooth crown dimensions in strabismic children and the relationship between the type of strabismus and tooth crown mesio-distal (M-D) and labio-lingual (L-L) size asymmetries. MATERIAL: Dental casts at mixed dentition of 2159 Collaborative Perinatal Study black and white children were measured, 123 of them strabismic at 1 year of age, age ranging from 6 to 12 years. METHODS: Directional and fluctuating asymmetries in antimeric teeth were explored in various types of strabismus having unilateral, bilateral or alternating expression. ANOVA and T-square test were used for size comparisons and calculated asymmetries were explored by comparing the variances and Pearson correlations. RESULTS: Strabismus was associated with significant M-D size increase of deciduous maxillary canines in black boys and white girls, black girls had size reduction in their mandibular canine, but white boys were unaffected. Right side size dominance was found in the strabismic children in the lower second deciduous molar M-D dimensions and in the children with alternating strabismus in their upper deciduous canine M-D dimensions. Children with unilateral strabismus had random fluctuating dental asymmetry in their upper deciduous second molar L-L dimensions when compared with healthy normals. Higher left-right correlations were found in lower second deciduous molar dimensions in strabismic girls when compared with that in controls and in strabismic boys, suggesting better developmental canalization in female. CONCLUSIONS: Asymmetries in the head area, such as promoted here in strabismic children, may have associations with asymmetries in the dentition, focusing the embryonal origins and timing of developmental processes.

Validity of the Hfm transgenic mouse as a model for hemifacial microsomia.

OBJECTIVE: Our comprehension of hemifacial microsomia (HFM) has been hindered by its diverse phenotype and unclear etiopathogenesis. The conventional view has been that HFM's facial defects result from embryonic hemorrhages in the region of the first and second branchial arches. A more recent model based on a transgenic mutation of a locus termed Hfm (B1 to B3 on chromosome 10) appears to provide an insight into HFM causation. This study investigated the validity of this model by examining the Hfm craniofacial phenotype and histological development of the embryonic head (E13.5 to 17.5). RESULTS: The results confirmed that although the loss-of-function mutation was transmitted in an autosomal dominant manner, the penetrance rate was significantly reduced and only Hfm heterozygotes were viable. The observations here extend the Hfm phenotype beyond microtia and jaw asymmetry to include structural and positional anomalies affecting the external auditory meatus, middle ear, cranial base, maxilla, and pharyngeal structures. Temporomandibular joint (TMJ) development and palatal shelf fusion were also affected in a small number of cases. In addition, some Hfm embryos displayed a novel finding: transposition of the developing inner ear between the tubotympanic recess and cranial base. CONCLUSIONS: These craniofacial features, especially the ear anomalies and facial asymmetry indicate that the Hfm transgenic mouse represents a useful model for the HFM-microtia spectrum. In particular, it supports the hypothesis that at least a proportion of HFM anomalies has a genetic causation mediated via mesenchymal disruptions and possibly embryonic hemorrhages.

Asymmetrical development of bones and soft tissues during eye migration of metamorphosing Japanese flounder, Paralichthys olivaceus.

The symmetrical body of flatfish larvae dramatically changes into an asymmetrical form after metamorphosis. Eye migration results in the most significant asymmetrical development seen in any vertebrate. To understand the mechanisms involved in eye migration, bone and cartilage formation was observed during metamorphosis in laboratory-reared Japanese flounder, Paralichthys olivaceus, by using whole-body samples and histological sections. Most of the hard tissues of the cranium (parasphenoid, trabecular cartilage, supraorbital canal, and supraorbital bar) exist symmetrically in the larval period before metamorphosis and develop by twisting in the same direction as that in which the eye migrates. An increase in skin thickness beneath the eye was observed only on the blind side at the beginning of eye migration; this was the first definitive difference between the right and left sides of the body. The pseudomesial bar, a peculiar bone present only in flatfishes, developed from this thick skin and grew dorsad. Novel sac-like structures were found and named retrorbital vesicles. The retrorbital vesicle of the blind side grew larger and faster than that of the ocular side when the right eye moved most dramatically, whereas no difference was observed between the volume of right and left connective tissue in the head. The asymmetrical presence and growth of the pseudomesial bar together with inflation of the retrorbital vesicle on the blind side may be responsible for right eye migration during metamorphosis in the Japanese flounder.

[Hemifacial microsomia. Embryological and clinical approach]. / Microsomies hémifaciales. Approche embryologique et clinique.

Hemifacial microsomia is an otomandibular dysplasia which includes congenital malformations affecting the jaw and ear apparatus. The knowledge of normal embryonic development is a prerequisite for optimal clinical management of those malformations. The development of craniofacial structures is a multi-step process, which involves many developmental events ranging from the migration of neural crest cells from the neural folds of the young neurula embryo to molecular signaling interactions that coordinate outgrowth and patterning of the facial primordia. Our current knowledge of craniofacial development is limited, but the use of animal developmental models will contribute significantly to our understanding of human otomandibular dysplasias. In this review we discuss both the classical and current aspects of otomandibular development. A clinical approach to hemifacial microsomia is proposed. Current pathogenetic hypotheses of hemifacial microsomia and also mandibulofacial dysostosis are reviewed.

Cranio-facial dysmorphism: experimental study in the mouse, clinical applications.

To obtain a better understanding of mandibulo-facial dysostosis and hemicraniofacial microsomia in man, the authors carried out a histologic and scanning electron microscope study of the facial malformations produced in mouse embryos by retinoic acid and methyl-triazene. The administration of 400 mg/kg 13 cis-retinoic acid (RA) to pregnant C57BL mice on day 9 of gestation produced anomalies of the cephalic extremity in the embryos resembling human mandibulo-facial dysostosis. The 64 embryos collected presented hypoplasia of the branchial arches or the snout in 79% of cases, auricular anomalies in 47% and ophthalmic anomalies in 12.5%. Fourteen NMRI mice on day 10.5 of gestation were treated with 1.5 mg (0.5 mg/kg) methyl-triazene (Methyl). The 126 embryos collected had developed a very high percentage of micromandibles and anomalies of both embryonic ears (94.6% to 100%). Finally, although the facial anomalies produced by retinoic acid resemble the human mandibulo-facial dysostosis syndrome, no correlation was found between hemicraniofacial microsomia and the administration of methyl-triazene.

Clinical appearance of spontaneous and induced first and second branchial arch syndromes.

The clinical appearance was investigated of 29 patients with mandibulofacial dysostosis, 26 with hemifacial microsomia, and seven with thalidomide-induced malformations affecting derivatives of the first and second branchial arches. Malformations of the external ear, ear canal, middle ear, zygoma, maxilla, mandible, and lower eye lid were prominent features of the syndromes. Facial nerve and 6th cranial nerve paralysis as well as anophthalmia or microphthalmia were seen only in patients with hemifacial microsomia and in the thalidomide-induced syndrome. We compared the clinical results with those in an animal model in which an induced first and second branchial arch syndrome depends on disturbed migration of neural crest cell during early embryogenesis. The critical time for a similar process in humans would be between the 20th and 29th days of pregnancy.