Craniofacial malformations: intrinsic vs extrinsic neural crest cell defects in Treacher Collins and 22q11 deletion syndromes

The craniofacial complex is anatomically the most sophisticated part of the body. It houses all the major sensory organ systems and its origins are synonymous with vertebrate evolution. Of fundamental importance to craniofacial development is a specialized population of stem and progenitor cells, known as the neural crest, which generate the majority of the bone, cartilage, connective and peripheral nerve tissue in the head. Approximately one third of all congenital abnormalities exhibit craniofacial malformations and consequently, most craniofacial anomalies are considered to arise through primary defects in neural crest cell development. Recent advances however, have challenged this classical dogma, underscoring the influence of tissues with which the neural crest cells interact as the primary origin of patterning defects in craniofacial morphogenesis. In this review we discuss these neural crest cell interactions with mesoderm, endoderm and ectoderm in the head in the context of a better understanding of craniofacial malformations such as in Treacher Collins and 22q11 deletion syndromes.

[Musculoskeletal connections. Study of two cases of oto-mandibular dysplasia]

The current genetic data stress the importance of musculo-skeletal connections in the development of a coherent system connecting the tendons and aponeurosis muscles with the osseous parts. The observations in tomodensitometry of musculo-skeletal connections in otomandibular dysostosis make it possible qualitatively to observe the development of the muscles and their functions.

Craniofacial development: the tissue and molecular interactions that control development of the head

The molecular cascades that control craniofacial development have until recently been little understood. The paucity of data that exists has in part been due to the complexity of the head, which is the most intricate regions of the body. However, the generation of mouse mutants and the identification of gene mutations that cause human craniofacial syndromes, together with classical embryological approaches in other species, have given significant insight into how the head develops. These studies have emphasized how unique the head actually is, with each individual part governed by a distinct set of signalling interactions, again demonstrating the complexity of this region of the body. This review discussed the tissue and molecular interactions that control each region of the head. The processes that control neural tube closure together with correct development of the skull, midline patterning, neural crest generation and migration, outgrowth, patterning, and differentiation of the facial primordia and the branchial arches are thus discussed. Defects in these processes result in a number of human syndromes such as exencephaly, holoprosencephaly, musculoskeletal dysplasias, first arch syndromes such as Riegers and Treacher-Collins syndrome, and neural crest dysplasias such as DiGeorge syndrome. Our current knowledge of the genes responsible for these human syndromes together with how the head develops, is rapidly advancing so that we will soon understand the complex set of molecular and tissue interactions that build a head.

Prenatal diagnosis and confirmation of the acrofacial dysostosis syndrome type Rodriguez

The group of acrofacial dysostosis (AFD) syndromes is very heterogeneous and contains many different entities. In 1990, Rodriguez et al. [1990: Am J Med Genet 35:484-489] described a new type of AFD characterized by severe mandibular hypoplasia, phocomelia and oligodactyly of the upper limbs, absence of fibulae, microtia, cleft palate, internal organ anomalies including arrhinencephaly and abnormal lung lobulation, and early lethality. We describe another case of AFD type Rodriguez, identified by prenatal ultrasonography at 25 weeks of gestation.

Increased levels of apoptosis in the prefusion neural folds underlie the craniofacial disorder, Treacher Collins syndrome

Treacher Collins syndrome (TCS) is an autosomal dominant disorder of human craniofacial development that results from loss-of-function mutations in the gene TCOF1. Although this gene has been demonstrated to encode the nucleolar phosphoprotein treacle, the developmental mechanism underlying TCS remains elusive, particularly as expression studies have shown that the murine orthologue, Tcof1, is widely expressed. To investigate the molecular pathogenesis of TCS, we replaced exon 1 of Tcof1 with a neomycin-resistance cassette via homologous recombination in embryonic stem cells. Tcof1 heterozygous mice die perinatally as a result of severe craniofacial anomalies that include agenesis of the nasal passages, abnormal development of the maxilla, exencephaly and anophthalmia. These defects arise due to a massive increase in the levels of apoptosis in the prefusion neural folds, which are the site of the highest levels of Tcof1 expression. Our results demonstrate that TCS arises from haploinsufficiency of a protein that plays a crucial role in craniofacial development and indicate that correct dosage of treacle is essential for survival of cephalic neural crest cells.

First and Second Branchial Arch Syndrome: Aspects on the Embryogenesis, Elucidations, and Rehabilitation Using the Osseointegration Concept

BACKGROUND

The osseointegration concept has dramatically changed the possibility of rehabilitating patients with craniofacial defects due to branchial arch syndromes.

PURPOSE

This article describes some problems related to the investigative routines and rehabilitation of individuals with malformations of the first and second branchial arches of the craniofacial region. Animal model systems have increased the knowledge of basic embryonic processes that can explain the extent of the malformations. Though most clinical first and second branchial arch syndromes are likely to be caused by sporadic mutations, inherited syndromes occur and also teratogenically induced syndromes are known. Prenatal diagnosis ruling out heredity and exogenous influence seems possible in the future. The possibility of preventing and alleviating fulminant syndromes prenatally also could be conceivable in the future.

PATIENTS AND METHODS

The rehabilitation process starts early after birth and should involve a team of specialists including clinical geneticists, pediatricians, audiologists, plastic surgeons, maxillofacial surgeons, otosurgeons, anaplastologists, speech pathologists, pedodontists, and orthodontists. With the development of the osseointegration concept in which craniofacial prostheses and hearing aids can be adapted on implants anchored in the craniofacial skeleton, a new field in the rehabilitation of these malformations has opened.

RESULTS

Important aspects in the use of the osseointegration concept include determination of the lowest age for implant surgery, accessibility of adequate bone for implants, the growth of the craniofacial skeleton during childhood, and the possibility for the patient and his or her parents to care for the skin penetration. Adverse tissue reactions, durability of craniofacial prostheses, and the possibility of unknown adverse reactions to metal implants in the body over a long time are other aspects of concern.

CONCLUSIONS

Patients with branchial arch syndromes benefit from a well-planned multidisciplinary rehabilitation process in which osseointegrated bone-anchored hearing aids and bone-anchored ear prostheses can be useful tools.

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.

Diamond-Blackfan anemia associated with Treacher-Collins syndrome

We describe a 2-year-old girl with a rare combination of congenital red cell aplasia or Diamond-Blackfan anemia (DBA) and Treacher-Collins syndrome (TCS). The anemia is only marginally responsive to high-dose corticosteroid, and the child is transfusion dependent. There is no one in the family affected with either DBA or TCS. A hypothesis is advanced that the simultaneous occurrence of the dysmorphism and erythroid agenesis in this case may have been the consequences of an insult to the fetus at the critical stage of development of maxillomandibular structure and the stage of primitive erythroid cell migration from the yolk sac to the fetal liver and bone marrow.

Is Far a Hox mutation?

The mouse First arch mutation, Far, causes a severe syndrome of craniofacial defects described previously. All of the known defects are derived from the anterior first arch, and to a very small extent, the dorsal second arch. Recently Far has been shown to be closely linked to Ulnaless on chromosome 2, and therefore in the vicinity of the Hox-4 gene cluster. This paper reports the results of several studies focused on the development origin of the most consistently expressed dominant effect caused by Far, an abnormal major bifurcation of the maxillary nerve. Nerve-stained whole-mount preparations of day 12 embryos showed that in Far mutants the maxillary nerve appears to have a central wedge missing from the normal single-stalked fan shape, and that the nerve defect in Far/Far and +/Far may be equally severe. The effect of retinoic acid on the development of the maxillary nerve was tested. Maternal treatment with 5 mg/kg retinoic acid on day 9 of gestation had no detectable effect on the maxillary nerve of +/Far embryos, and similar treatment with a teratogenic dosage (20 mg/kg) on day 8 or 9 produced no Far-like maxillary nerve defects in genetically normal embryos. The neural crest cells that give rise to nerves and mesenchyme of the first arch originate from specific rhombomeres, discrete segments of the developing head. The rhombomeres of 15 embryos at the 14-23 somite stages, of which 75% are expected to be +/Far or Far/Far, were examined. There was no detectable defect in segmentation or morphology of the rhombomeres compared with controls. The significance of ectopic cartilage in the palate of Far/Far mutants in relation to nerve bifurcation was explored. In histological studies, five out of six Far/Far day-15 fetuses had a rod of ectopic cartilage lateral to the posterior palate, running parallel to, and morphologically similar to, Meckel's cartilage, and lying between the two trunks of the abnormally bifurcated maxillary nerve. None of six +/Far day-15 fetuses examined had detectable ectopic cartilage in this region. We hypothesize that the maxillary nerve defects in Far mutants may be explained by the presence of an ectopic precartilaginous blastema that does not always further develop into detectable cartilage. The ectopic cartilage found in Far/Far resembles the epibranchial cartilage expressed in more posterior branchial arches and in the first arch of lower organisms, and therefore may represent an atavistic posteriorization of the anterior first arch in Far mutants.(ABSTRACT TRUNCATED AT 400 WORDS)

[Role of the neural crest in maxillofacial malformations: facts and hypotheses]

The occurrence of neural crest defects has been postulated in the genesis of several maxillo-facial malformations. It seems to be the case for mandibulo-facial dysostosis and holoprosencephaly.

Pathogenesis of cleft palate in Treacher Collins, Nager, and Miller syndromes

Abnormalities of the secondary palate were studied in an animal model in which features of Treacher Collins syndrome (TCS) and Nager or Miller syndromes (both of which are facially similar to Treacher Collins, but include limb malformations) were induced by acute maternal exposure to 13-cis-retinoic acid (13-cis-RA, isotretinoin, Accutane). Previous work in our laboratory has illustrated that excessive cell death in the proximal aspect of the maxillary and mandibular prominences of the first visceral arch and in the apical ectodermal ridge of the limb bud probably accounts for the characteristic craniofacial and limb abnormalities observed (Sulik et al, 1987; Sulik and Dehart, 1988). The current study shows that maternal treatment with 400 mg per kilogram 13-cis-RA at 8 days 14 hours (8d14hr) or 9d6hr post fertilization results in abnormalities of the secondary palate that vary in incidence and severity. Following the earlier treatment time, 82 percent (68 of 74) of the 18d fetuses were affected, with, severely hypoplastic, unfused palatal shelves present in 34 percent (25 of 74). The less severely affected fetuses had malformations that involved primarily the posterior aspect of the palatal shelves. This malformation (foreshortening of the posterior portion of the palate) constituted the major developmental alteration that resulted from treatment at the later time, at which time a 52 percent (26 of 50) malformation incidence was seen. The change in pattern of malformations with treatment time is consistent with the changing pattern of programmed cell death, which was observed to occur in the first visceral arch.

[Facial malformations and asymmetries caused by the first and second branchial arch syndrome]

The first and second branchial arch syndrome is a congenital affection, among whom one can range as well hereditary as non-hereditary entities. They always cause a badly mutilating facial asymmetry. In this article, the first and second branchial arch syndrome were divided in hemifacial and bilateral dysostoses. We pointed out the hemifacial microsomia, the most occurring entity in these series. From two case reports, we attempt to give a treatment synopsis of this syndrome, which is always done by a multi-disciplinary team, including dentists, orthodontists, maxillofacial surgeons and plastic surgeons.

[Mandibulofacial dysostosis or Franceschetti-Zwahlen-Klein syndrome: apropos of 2 cases]

The Authors report two cases of mandibulofacial dysostosis: a three-months-old girl who presented with palpebral fissures in an antimongoloid direction, cleft palate, coloboma of the lower lid, hypoplasia of the malar bones and mandible, malformation of the external ears, two clefts between the mouth and left ear, minimal naso-frontal angle and a one-month-old boy who presented with similar structural deformities. These features can be considered characteristic of mandibulofacial dysostosis, whose most common finding is the presence of bilateral signs.

Ocular and facial maldevelopment: the role of neural crest

Three children are described who show a spectrum of clinical abnormalities affecting their eyes and non ocular tissues. These entities are best explained as disorders of neural crest migration and once recognised should lead to a search for other systemic developmental disorders. The mechanism of combined facial skeleton and eye malformation is discussed in the light of our current understanding of ocular embryology, and the justification for considering these and other entities as examples of Neurocristopathies is explored.

[Associated morphological anomalies of the face and brain in infants]

Thirty-nine malformations and morphological abnormalities of the brain are analysed among a group of 300 children presenting facial malformations or dysembryoplasias (13%) between 1979 and 1986. Holoprosencephaly was discovered associated with bilateral labiomaxillary cleft in 25% of cases and an abnormality of brain stem was observed in 13% of cases with maxillo-mandibular dysostosis. This high incidence, due to the bias of hospital recruitment, confirms the recent experimental studies on embryonic development demonstrating the common neural origin of the face and brain, between which there is a topographic correspondence. To the nasofronto-premaxillary structures corresponds the whole prosencephalon and to the maxillo-mandibular areas correspond the brain stem and its nerves. The demonstration of the neural crest's role in the morphogenesis of the facial mesenchyme, the meninges and the nerves further confirms these associations of malformations in phacomatoses or neurocristopathies. Thus, the face appears as a marker of the development of the brain.

Mandibulofacial dysostosis (Treacher Collins syndrome): a new proposal for its pathogenesis

Acute exposure to 400 mg/kg 13-cis retinoic acid (13-cis RA, isotretinoin, Accutane) on the ninth day postfertilization in mice (a time that corresponds to the fourth week postfertilization in humans) results in malformations that characterize mandibulofacial dysostosis (MFD, Treacher Collins syndrome). Deficiencies in the infraorbital region and in the mandibular ramus and condyle, abnormalities of the secondary palate, and external ear malformations were observed. Light and scanning electron microscopic analyses of affected embryos illustrate that within 12 hours of maternal 13-cis RA treatment, markedly excessive (possibly premature) cell death occurs in regions where some of the cells are normally destined to undergo programmed cell death. Previous studies with retinoids have shown that they labilize lysosomal membranes and expand and strengthen regions of programmed cell death. Of particular interest for this study was cell death occurring in the dorsal (proximal) aspects of the maxillary and mandibular prominences of the first visceral arch, the second visceral arch, and the first visceral cleft, areas that correspond to the locations of the first and second arch ectodermal ("ganglionic") placodes and first closing membrane, respectively. The derivatives of this region are those that are severely affected in MFD. As described in previous reports from this laboratory, 13-cis RA is known to interfere with neural crest cells, resulting in major craniofacial malformations. However, the exposure times involved were earlier than those described herein. It is hypothesized that effects on the first and second arch ectodermal placodal cells at a time following the release from the neural folds of neural crest cells into the developing cranial region are of great significance in the pathogenesis of MFD. This is in contrast to the prevailing hypothesis that these malformations are the direct result of a primary interference with neural crest cells.

A new autosomal dominant acrofacial dysostosis syndrome

We report on a family in which a previously undescribed acrofacial dysostosis syndrome is segregating as an autosomal dominant trait. Craniofacial manifestations are those of mild mandibulofacial dysostosis and are quite constant among affected relatives. The acral abnormalities are quite variable, affecting predominantly the radial ray. Variability extends from thumb duplication in one patient to mild hypoplasia of the first metacarpal and first proximal phalanx in most affected individuals. Mandibulofacial dysostosis is a causally nonspecific malformation and as such represents an apparently monotopic developmental field defect. Its occurrence with acral anomalies in several conditions of different cause represents a polytopic developmental field defect.

The continuity of mandibular form in mandibulofacial dysostosis

It is reported in studies of patients with Mandibulofacial Dysostosis (Treacher Collins Syndrome, MFD) that the lower border of the mandible exhibits a consistent form. The mandible of a 15-week-old fetus was described demonstrating the distinctive typical broad concave curvature of the lower border of the mandible. It appears that the basic mandibular form in MFD is established in utero, is maintained throughout postnatal growth and development, and is unique in shape.

The embryological basis of craniofacial dysplasias

Craniofacial dysplasia of a syndromic pattern can usually be classified into one of two easily identifiable groups. In the first group are those malformations of the craniofacial skeleton and soft tissues that are asymmetrical in form and in the other, those that are principally symmetrical. Clinical studies have demonstrated that affected subjects in the symmetrical group frequently improve in terms of facial appearance as growth and development proceed to maturity, while those with asymmetrical defects often deteriorate in this respect. Embryological studies on animal models of these malformations have shown that asymmetrical lateral facial dysplasia and symmetrical mandibulofacial dysplasia exhibit discrete and widely disparate causal mechanisms of malformation. Analysis of these mechanisms and their effects on subsequent growth and development has suggested significant variations in the timing and technique of reconstructive procedures which will enable the surgeon to produce the most effective results when used for the rehabilitation of the afflicted.

Prenatal mandibulofacial dysostosis (Treacher Collins syndrome)

The clinical, radiographic, and histologic aspects of Mandibulofacial Dysostosis (Treacher Collins Syndrome)--MFD--are described as observed in a human fetus of approximately 15 weeks gestation age. Findings in the present study do not differ significantly from those previously reported, as the abnormal fetus exhibited the peculiar ocular, otic, and mandibular defects common in descriptions of postnatal survivors. Although exhibiting the major signs and symptoms of MFD even at this early developmental stage, previously unreported relationships dealing with the ossification of the mandible and salivary gland hyperplasia are noted. Contrary to expectation, vascularization appears excessive. The pathogenesis of the events leading to the deformities of the first and second branchial arches is extrapolated to seven weeks in utero.

Studies of malformation syndromes of man XXXXIA: anatomical studies in the Hanhart syndrome--a pathogenetic hypothesis

Two infants with the Hanhart syndrome, i.e. micrognathia, microglossia, terminal deficiency of all limbs and imperforate anus in one, were dissected and studied in detail. The interrelationships of the muscular and skeletal defects suggested that they were the result of incomplete rather than abnormal morphogenesis. We speculate that the oral and limb abnormalities resulted from deficient mesodermal proliferation caused by disturbances in the ectodermal-mesodermal interactions beginning about the 4th week of development. The imperforate anus may also relate to the proposed defect.

The pathogenesis of the Treacher Collins syndrome (mandibulofacial dysostosis)

Numerous synonyms have been used to describe syndromes affecting structures derived from the first and second branchial arches. These conditions are most conveniently grouped into the asymmetrical anomalies of hemifacial microsomia and the symmetrical syndrome of mandibulofacial dysostosis. By examination of animal models of these conditions it can be demonstrated that the pathogenesis is distinct but different for each group. The characteristic facies of mandibulofacial dysostosis suggests a mechanism of malformation which operates early in embryogenesis, acting uniformly on parts which are derived from neural crest cells. In the serial examination of a phenocopy of mandibulofacial dysostosis, induced in the rat by the teratogen vitamin A, focal death of pre-otic neural crest cells is observed to occur, creating both a spatial rearrangement of the developing ears and a paucity of ectomesenchyme in the first and second branchial arches. The result of these deviations from normal morphogenesis is the development of a facial skeleton which is symmetrical but distinctly different in form from that in the normal animal. Microscopic study of the induced ear and jaw defects revealed that the animal model was closely comparable in all respects to human mandibulofacial dysostosis. The specific nature of the interaction between teratogen and migrating neural crest cells is not yet clear; nor is it known whether these cells are attacked before or after their specific destination is determined. The greater part of the damage is inflicted in a general fashion and leads to symmetrical abnormal development. Minor examples of dyssymmetry do occur, however, in the animal model and man, but these are compatible with the hypothesis of a pathogenetic mechanism which is initiated centrally and symmetrically but modified locally at a later stage. A description of the pathogenesis of these two conditions, scientific predictions can be made with respect to the timing and technique of reconstruction of the orofacial defects, and the effects of surgery on growth and development.

Maxillomandibular ankylosis and cleft palate in rat embryos

Balanced embryologic development of the oral structures is vital for the fusion of the secondary palate. A malformation such as maxillomandibular ankylosis created by heterotopic cartilage in embryos of vitamin A-treated rats can lead to a chain of events that results in cleft palate and other malformations.