Agnathia, situs inversus, and associated malformations

Free Fibula Flap for the Treatment of Agnathia in a 10-Year-Old With Severe Agnathia-Otocephaly Complex

Agnathia-otocephaly complex (AOC), a first branchial arch defect, is characterized by mandibular hypoplasia or aplasia, ear abnormalities, microstomia, and macroglossia and is a rare and often fatal diagnosis. Herein, the technical considerations and details of mandibular reconstruction using virtual surgical planning (VSP) and a vascularized free fibula flap for further mandibular reconstruction in a 10-year-old boy are presented. The patient's preoperative examination was consistent with agnathia (absence of mandibular symphysis, bilateral mandibular bodies, condyles, coronoids, rami, and temporomandibular joint), severe microstomia, and a Tessier # 30 cleft (maintained to allow oral access until later in treatment). Virtual surgical planning was utilized to plan a 3-segment fibula for the reconstruction of the mandibular symphysis and bilateral body segments, and bilateral costochondral grafts were planned for the rami. To the authors' knowledge, this represents the first application of virtual surgical planning for mandibular reconstruction with a vascularized free fibula flap in a pediatric patient with severe agnathia-otocephaly complex.

A case of rare isolated agnathia and literature review

Agnathia is a rare congenital malformation with unknown etiology characterized by absence of the mandible, microstomia, and tongue aplasia, often found to have other anomalies including holoprosencephaly. The purpose of this paper was to describe the symptoms and imaging of a case of isolated agnathia and to conduct a comprehensive literature review of reported patients with isolated agnathia. Case reports of isolated agnathia are very rare, with most infants as stillborn. We report a child's management of isolated agnathia with microstomia and tongue aplasia. A literature review was performed with focus on diagnosis, airway, and feeding management of isolated agnathia. Polyhydramnios was a common pregnancy complication reported in 25 out of the 39 patients in the case study. Five infants were stillborn, while 23 died within the neonatal period. Of the deceased infants within the neonatal period, 19 died within minutes to hours while four died within days to weeks. There are nine patients with agnathia that survived past infancy. The results of this study suggest that isolated agnathia is a rare malformation which requires a multi-disciplinary approach for airway and feeding management.

Re-focusing on Agnathia-Otocephaly complex

OBJECTIVES

Agnathia-otocephaly complex is a rare condition characterized by mandibular hypoplasia or agnathia, ear anomalies (melotia/synotia) and microstomia with aglossia. This severe anomaly of the first branchial arch is most often lethal. The estimated incidence is less than 1 in 70.000 births, with etiologies linked to both genetic and teratogenic factors. Most of the cases are sporadic. To date, two genes have been described in humans to be involved in this condition: OTX2 and PRRX1. Nevertheless, the overall proportion of mutated cases is unknown and a significant number of patients remain without molecular diagnosis. Thus, the involvement of other genes than OTX2 and PRRX1 in the agnathia-otocephaly complex is not unlikely. Heterozygous mutations in Cnbp in mice are responsible for mandibular and eye defects mimicking the agnathia-otocephaly complex in humans and appear as a good candidate. Therefore, in this study, we aimed (i) to collect patients presenting with agnathia-otocephaly complex for screening CNBP, in parallel with OTX2 and PRRX1, to check its possible implication in the human phenotype and (ii) to compare our results with the literature data to estimate the proportion of mutated cases after genetic testing.

MATERIALS AND METHODS

In this work, we describe 10 patients suffering from the agnathia-otocephaly complex. All of them benefited from array-CGH and Sanger sequencing of OTX2, PRRX1 and CNBP. A complete review of the literature was made using the Pubmed database to collect all the patients described with a phenotype of agnathia-otocephaly complex during the 20 last years (1998-2019) in order (i) to study etiology (genetic causes, iatrogenic causes…) and (ii), when genetic testing was performed, to study which genes were tested and by which type of technologies.

RESULTS

In our 10 patients' cohort, no point mutation in the three tested genes was detected by Sanger sequencing, while array-CGH has allowed identifying a 107-kb deletion encompassing OTX2 responsible for the agnathia-otocephaly complex phenotype in 1 of them. In 4 of the 70 cases described in the literature, a toxic cause was identified and 22 out the 66 remaining cases benefited from genetic testing. Among those 22 patients, 6 were carrying mutation or deletion in the OTX2 gene and 4 in the PRRX1 gene. Thus, when compiling results from our cohort and the literature, a total of 32 patients benefited from genetic testing, with only 34% (11/32) of patients having a mutation in one of the two known genes, OTX2 or PRRX1.

CONCLUSIONS

From our work and the literature review, only mutations in OTX2 and PRRX1 have been found to date in patients, explaining around one third of the etiologies after genetic testing. Thus, agnathia-otocephaly complex remains unexplained in the majority of the patients, which indicates that other factors might be involved. Although involved in first branchial arch defects, no mutation in the CNBP gene was found in this study. This suggests that mutations in CNBP might not be involved in such phenotype in humans or that, unlike in mice, a compensatory effect might exist in humans. Nevertheless, given that agnathia-otocephaly complex is a rare phenotype, more patients have to be screened for CNBP mutations before we definitively conclude about its potential implication. Therefore, this work presents the current state of knowledge on agnathia-otocephaly complex and underlines the need to expand further the understanding of the genetic bases of this disorder, which remains largely unknown.

CLINICAL RELEVANCE

We made here an update and focus on the clinical and genetic aspects of agnathia-otocephaly complex as well as a more general review of craniofacial development.

Prenatal Diagnosis of Isolated Agnathia-Otocephaly: A Case Report and Review of the Literature

Agnathia is a rare disease characterized by the absence of a mandible. Few cases of prenatally diagnosed isolated agnathia have been reported. We present a case report and review of the literature of prenatally diagnosed agnathia. A 38-year-old woman (gravida 0, para 0) was referred to our hospital at 28 weeks and 3 days of gestation for fetal evaluation because of polyhydramnios and suspected facial anomalies. Three-dimensional ultrasonography and MRI indicated agnathia. Premature rupture of the membranes occurred before the parents could reach a decision on the postnatal treatment. We performed emergency cesarean section on the second day of the 33rd week of gestation. The neonate was deemed nonresuscitable and he died of airway obstruction shortly after birth. Because agnathia is associated with very poor prognosis, accurate prenatal diagnosis and detailed counseling should be promptly provided before unexpected delivery to the parents for the determination of postnatal treatment.

Severe Agnathia-Otocephaly Complex: Surgical Management and Longitudinal Follow-up From Birth Through Adulthood

Agnathia-otocephaly complex (AOC) is characterized by mandibular hypo- or aplasia, ear abnormalities, microstomia, and microglossia. Though rare and often fatal, this is the first report detailing various reconstructive strategies beyond infancy as well as longitudinal follow-up into adulthood. All patients with AOC treated at our institution over a 30 year period were reviewed. Four patients were identified, one with agnathia, one with micrognathia. Two males with nanognathia (defined as a symphyseal remnant without body nor ramus) were also included. The mean follow-up was 17 years. All four underwent perinatal tracheostomy and gastrostomy-tube placement. Commissuroplasties were typically performed before 3 years of age and repeated as necessary to allow for oral hygiene. Mandibular reconstruction was most successful with rib between ages 3 and 8, after which time, free fibula transfer was utilized. Due to some resoprtion or extrusion, all patients underwent repeated bone grafting procedures. Tissue expansion of the neck was used to restore the lower third of the face, but was most successful in the teenage years. At last follow-up of the eldest patients, one was in college while another was pursuing graduate education. AOC need not be a fatal nor untreatable condition; a reasonable quality of life can be achieved. Although the lower-facial contour may be improved, and a stoma created, the lack of musculature make deglutition virtually impossible with current therapies. Just as transplantation has emerged as a modality for facial restoration following severe trauma, so too may it be a future option for congenital deformities.

Agnathia-otocephaly complex: a case report and examination of the OTX2 and PRRX1 genes

Agnathia-otocephaly is a rare, often lethal malformation characterized by absence or hypoplasia of the mandible, microstomia, hypoglossia/aglossia, and variable anterior midline fusion of the ears (melotia, synotia). Etiologies have been linked to both genetic and teratogenic factors and to date, a definitive, commonly identifiable cause has not been recognized. Mouse and human genetic studies have implicated OTX2 and PRRX1 as potential candidate genes for agnathia-otocephaly. In this study we report a sporadic case of agnathia-otocephaly complex with associated features of maldevelopment and examine the roles of OTX2 and PRRX1. The proband, a male born at 31 weeks, displayed severe micrognathia, microstomia, posteriorly-rotated and low set ears, and downward slanting palpebral fissures. Mutation analysis was performed after sequencing the entire coding regions of OTX2 and PRRX1 genes isolated from the proband and his parents. After thorough analysis, no DNA variations were detected. This suggests that mutations in different genes or environmental causes are responsible.

Holoprosencephaly and agnathia spectrum: Presentation of two new patients and review of the literature

Holoprosencephaly (HPE), the most common developmental disorder of the human forebrain, is occasionally associated with the spectrum of agnathia, or virtual absence of the mandible. This condition results in a constellation of structural cerebral and craniofacial abnormalities. Here we present two new patients and review 30 patients from the literature with HPE and variants of agnathia. The majority of these patients are female and have the most severe forms of HPE, with cyclopia present more frequently than is usually observed in cohorts of patients with HPE. Also, many patients have additional clinical findings not typical in patients with classic HPE, particularly situs abnormalities. Recent animal studies suggest that the association of HPE and agnathia may relate to alterations in signaling from forebrain and foregut endoderm organizing centers and subsequent first pharyngeal arch development, although present models are inadequate to explain all of the clinical findings of this enigmatic human syndrome. Further research is required to better elucidate the causal and pathogenic basis of this association.

Magnetic resonance microscopy defines ethanol-induced brain abnormalities in prenatal mice: effects of acute insult on gestational day 7

BACKGROUND

This magnetic resonance microscopy (MRM)-based report is the second in a series designed to illustrate the spectrum of craniofacial and central nervous system (CNS) dysmorphia resulting from single- and multiple-day maternal ethanol treatment. The study described in this report examined the consequences of ethanol exposure on gestational day (GD) 7 in mice, a time in development when gastrulation and neural plate development begins; corresponding to the mid- to late third week postfertilization in humans. Acute GD 7 ethanol exposure in mice has previously been shown to result in CNS defects consistent with holoprosencephaly (HPE) and craniofacial anomalies typical of those in Fetal Alcohol Syndrome (FAS). MRM has facilitated further definition of the range of GD 7 ethanol-induced defects.

METHODS

C57Bl/6J female mice were intraperitoneally (i.p.) administered vehicle or 2 injections of 2.9 g/kg ethanol on day 7 of pregnancy. Stage-matched control and ethanol-exposed GD 17 fetuses selected for imaging were immersion fixed in a Bouins/Prohance solution. MRM was conducted at either 7.0 Tesla (T) or 9.4 T. Resulting 29 microm isotropic spatial resolution scans were segmented and reconstructed to provide 3D images. Linear and volumetric brain measures, as well as morphological features, were compared for control and ethanol-exposed fetuses. Following MRM, selected specimens were processed for routine histology and light microscopic examination.

RESULTS

Gestational day 7 ethanol exposure resulted in a spectrum of median facial and forebrain deficiencies, as expected. This range of abnormalities falls within the HPE spectrum; a spectrum for which facial dysmorphology is consistent with and typically is predictive of that of the forebrain. In addition, other defects including median facial cleft, cleft palate, micrognathia, pituitary agenesis, and third ventricular dilatation were identified. MRM analyses also revealed cerebral cortical dysplasia/heterotopias resulting from this acute, early insult and facilitated a subsequent focused histological investigation of these defects.

CONCLUSIONS

Individual MRM scans and 3D reconstructions of fetal mouse brains have facilitated demonstration of a broad range of GD 7 ethanol-induced morphological abnormality. These results, including the discovery of cerebral cortical heterotopias, elucidate the teratogenic potential of ethanol insult during the third week of human prenatal development.

Otocephaly

Otocephaly is a rare lethal syndrome of microstomia, aglossia, agnathia, and synotia. This male infant was born to a 19-year-old, gravida 1, para 0, woman who received routine prenatal check-up. Polyhydramnios, low-lying ears, and proboscis were noted by sonography at 29 weeks of gestation. Amniocentesis showed a normal karyotype of 46, XY. Premature rupture of membranes and preterm labor were noted at 32 weeks of gestation. A male infant was delivered preterm and died shortly after birth. The infant showed midline proboscis and absence of mandible. The simple, soft ears were extremely low-set and were near the midline of the neck. Otocephaly is regarded as the most severe form of first arch anomalies. Prenatal diagnosis should be dependent on ultrasound analysis. In the face of polyhydramnios, otocephaly is one of the possible fetal anomalies.

Otocephaly: report of five new cases and a literature review

Otocephaly, characterized by mandibular hypoplasia or agnathia, ventromedial auricular malposition (melotia) and/or auricular fusion (synotia), and microstomia with oroglossal hypoplasia or aglossia, is an extremely rare anomalad, identified in less than 1 in 70,000 births. The malformation spectrum is essentially lethal, because of ventilatory problems, and represents a developmental field defect of blastogenesis primarily affecting thefirst branchial arch derivatives. Holoprosencephaly is the most commonly identified association, but skeletal, genitourinary, and cardiovascular anomalies, and situs inversus have been reported. Polyhydramnios may be the presenting feature, but prenatal diagnosis has been uncommon. We present five new cases of otocephaly, the largest published series to date, with comprehensive review of the literature and an update of research in the etiopathogenesis of this malformation complex. One of our cases had situs inversus, and two presented with unexplained polyhydramnios. Otocephaly, while quite rare, should be considered in the differential diagnosis of this gestational complication.

Prenatal sonographic diagnosis of isolated agnathia: a case report

Agnathia is a rare malformation characterized by the absence of the mandible, microstomia, aplasia or hypoplasia of the tongue, and low-set or medially fused ears. It occurs alone or in combination with a variety of malformations such as holoprosencephaly. All previous cases of the prenatal diagnosis of agnathia have been accompanied with fatal anomalies. We report here the first case of isolated agnathia, which was diagnosed by prenatal sonography at 32 weeks of gestation. In this case, prenatal sonographic examination showed the severe defect of the chin, small opening of the mouth and severe polyhydramnios. There was no sonographic evidence of holoprosencephaly or anomalies in other organ systems. The diagnosis was confirmed postnatally.

Agnathia-otocephaly complex: Report of three cases with involvement of two different Carnegie stages

Three fetuses with agnathia-otocephaly complex representing different degrees of embryonic maldevelopment are reported. The study of the three cases and of the anterior embryonic disc supports the concept that an altered embryologic development might have taken place at Carnegie stages 10 (embryonic days 22 or 23) and 11 (embryonic days 23-26). Karyotypic abnormalities and aberrant gene expression of sonic hedgehog and paired-related homeobox genes are discussed as the cytogenetic and molecular basis of agnathia-otocephaly complex.

Situs inversus totalis and congenital hypoglossia

Hypoglossia is a rare congenital malformation, occurring either as an isolated malformation or in association with other deformities, particularly limb defects. We describe a female infant with congenital hypoglossia, micrognathia and situs inversus. The main complications were airway compromise and feeding difficulties requiring tracheostomy and gastrostomy. Situs inversus and hypoglossia have been reported together on six previous occasions, with all cases being sporadic. Situs inversus-hypoglossia falls into a spectrum of aetiologically non-specific developmental field defects that includes the Aglossia-adactylia spectrum and the Agnathia-holoprosencephaly spectrum. Situs inversus-hypoglossia may represent a mild form of Agnathia-holoprosencephaly.

Prenatal diagnosis of agnathia-holoprosencephaly: three-dimensional imaging by helical computed tomography

We report a case of agnathia-holoprosencephaly which was prenatally diagnosed based on helical computed tomography (CT) images obtained at 23 weeks of gestation. Ultrasound examination first showed the presence of alobar holoprosencephaly, but the facial structures were not clearly detailed. However, three-dimensional imaging by helical CT precisely demonstrated the most striking feature of agnathia: absence of the mandible. This technique provided us valuable information that contributed to the in utero diagnosis. In utero helical CT is a useful examination tool for the diagnosis of osteogenic abnormalities.

[Renal cell carcinoma in patient with situs inversus and Kartagener syndrome]

A case of a adenocarcinoma renal in a patient with situs inversus complete to which was associated bronchiectasis and chronic sinusitis (kartagener's syndrome) is reported. It is the third case described in the international literature of a renal cells carcinoma in a patient with situs inversus totalis and the first in patient the one which has the triada classic of the kartagener's syndrome plus sterility. The tumor was discovered in a way incidental upon accomplishing a TAC toracoabdominal and was solved through nefrectomia for lumbotomy approach.

[Hypoglossia, situs inversus and absence of the pituitary in a neonate: teratogenic effect of maternal hyperthermia?]

Hypoglossia is a rare malformation that is not fatal, unlike otocephaly.

CASE REPORT

A neonate, born at 39 weeks of GA and dead at 5th day showed hypoglossia, dextrocardia, situs inversus and pituitary aplasia. Maternal hyperthermia was observed at 4 weeks gestation.

CONCLUSION

This case is reminiscent of a community of syndrome with agnathia-holoprosencephaly and situs inversus. The responsibility of maternal hyperthermia is raised.

Goldenhar sequence and mosaic trisomy 22

We describe a term infant with facioauriculo-vertebral "dysplasia" (Goldenhar sequence), hypertelorism, and mosaic trisomy 22: peripheral blood, 46, XY/47, XY, + 22 (72%/28%); skin fibroblasts, 47, XY, + 22 (100%). This is the second report of Goldenhar anomaly with epibulbar dermoids in a liveborn infant with aneuploidy. Hypertelorism is rare in Goldenhar sequence, but typical of trisomy 22. We recommend chromosome analysis in all patients with Goldenhar sequence. Those with hypertelorism may be more likely to have aneuploidy as well.

Perspectives on craniofacial asymmetry. I. The biology of asymmetry

Part I introduces the survey and presents a topic outline of the six parts that make up this series of articles on craniofacial asymmetry. The discussion in Part I considers normal variation, normal and abnormal laterality, types of anomalies that may be asymmetric, and finally, some well-known causes of craniofacial asymmetry.

Renal cell carcinoma with situs inversus totalis

A case of renal cell carcinoma in a patient with situs inversus totalis is reported. Only 8 cases of malignant neoplasms have been reported in situs inversus totalis, and our case represents the second case report of renal cell carcinoma in a patient with situs inversus totalis. The frequency of situs inversus totalis is between 1 in 8,000 and 1 in 20,000. Cardiac and pulmonary anomalies are common in patients with situs inversus totalis. Renal anomalies, including agenesis, dysplasia, hypoplasia, ectopia, polycystic kidney, and horseshoe kidney, have been reported. Because of the association between situs inversus and cardiac, pulmonary, renal, and vascular anomalies, management of the patient with situs inversus and urologic disease requires careful preoperative evaluation.

A case of agnathia, situs inversus, and a normal central nervous system

We report here a premature female infant with agnathia, low-set but normally formed ears, a downward eye slant, choanal atresia and a cleft palate. She had severe respiratory distress and died despite maximum intervention at 5 days of age. Autopsy revealed situs inversus totalis; crossed fused renal ectopia; agnathia; normal thyroid, larynx, trachea, and bronchi; incomplete lobation of the lungs; immature pulmonary development with early hyaline membranes; and a normal central nervous system. This lack of significant central nervous system abnormalities distinguishes this infant from the majority of previously reported infants with agnathia and situs inversus.

A long surviving case of holoprosencephaly agnathia series

The rare syndrome of the agnathia with microstomia, aglossia, synotia (the external ears approaching one another in the midline) and brain malformation (agnathia-holoprosencephaly) was reported by Pauli et al. (1983) as a developmental field defect. This syndrome has two subgroups. One is more severe with brain malformation (holoprosencephaly), and the other is less severe without brain malformation. This report presents a long surviving case of this syndrome without brain malformation.

Astomia-agnathia-holoprosencephaly association. Prenatal diagnosis of a new case

A case of agnathia-astomia-holoprosencephaly with prenatal ultrasound diagnosis at 23 weeks is reported and discussed. This lethal neurocristopathy, well known in mammalians, is rarely observed in humans. Prenatal diagnosis features are intrauterine growth retardation, mandibular absence or major hypoplasia, holoprosencephaly, cyclopia or hypotelorism, and in some instances frontal proboscis. This malformation is usually sporadic, but may be genetically determined as an autosomal recessive trait, since two cases in the same sibship have been reported.

Agnathia, holoprosencephaly, and situs inversus: a third report

We report on a male infant with cyclopia, agnathia, and situs inversus. In addition, anal atresia and horseshoe-kidneys were present. To our knowledge, this is the third published case of the "agnathia-holoprosencephaly-further midline defects association."

Otocephaly-midline malformation association

Otocephaly ("agnathia") is a developmental field complex with structural defects limited to the craniofacial region. Previously, two infants with otocephaly, situs inversus totalis, renal defects, and vertebral and rib abnormalities were reported by Pauli et al. [Teratology 23:85-93, 1981]. We describe a similarly affected infant male, supporting the existence of this midline malformation association. A generalized disturbance in cell migration from the primitive streak may be its pathogenesis. A search for additional patients among cases of otocephaly may establish its prevalence, patterns of associated anomalies, and cause.

Perspectives on holoprosencephaly: Part III. Spectra, distinctions, continuities, and discontinuities

This paper attempts to balance our knowledge of holoprosencephalic spectra and continuities with important distinctions and discontinuities. Prevalence studies and syndrome delineation are briefly reviewed. The following topics receive detailed coverage: human teratogens, special aspects of forebrain and hindbrain malformations, aprosencephaly/atelencephaly, association with neural tube defects, current assessment of "facial principles," and endocrine abnormalities.

Agnathia, holoprosencephaly, and situs inversus: report of a case

We present the first documented case of agnathia-holoprosencephaly (an uncommon form of craniofacial anomaly) associated with situs inversus. This case may represent the concordance of multiple field complex anomalies, but the possibility of a major midline malformation (situs inversus) caused by a timed insult (environmental or genetic) which affects multiple structures and occurs concurrently with a major field defect during early embryogenesis cannot be excluded.

Renal cell carcinoma in a patient with situs inversus totalis

Situs inversus occurs with a frequency of about 1 in 8,000. We present a case of renal cell carcinoma in a patient with situs inversus totalis treated with nephrectomy. Uneventful operative management was attained by adequate preoperative radiologic evaluation.

Monozygotic twin aborted fetuses discordant for holoprosencephaly/synotia

A pair of monozygotic twin fetuses aborted at 15 weeks were found to be discordant for holoprosencephaly and synotia. They were studied grossly, radiologically, and histologically. Features of first brancial arch dysplasia (synotia, agnathia, and astomia) and holoprosencephaly (absent ethmoid bone and Rathke's pouch) observed in one twin were contrasted with minimal dysmorphology in the co-twin. Some evidence of the twin transfusion syndrome was also apparent, perhaps contributing to the twins' spontaneous abortion.

An anatomical study of human otocephaly

This study describes the gross anatomic variations observed in a 32-week male fetus diagnosed as having otocephaly. Special attention was given to the muscular, peripheral nervous, and vascular systems of the entire body. External features included approximation of the ears on the front of the neck, underdevelopment of the lower jaw, and a small oral cavity. The mandible, maxillae, and zygomatic bones were smaller than normal and appeared shifted in a ventrocaudal direction. The middle ear ossicles were fused and abnormally positioned. The tongue was positioned abnormally and malformed. The muscles of mastication were fused in the midline and formed the floor of the oral cavity. The variations were similar to the spectrum of abnormalities reported in two cases in the literature. Because of this finding, it is possible that the causative events leading to these deviations were similar in the three cases. Possible mechanisms are considered which could lead to the observed malformations seen in these cases. There were also several muscle and nerve anomalies outside of the head region.

Familial agnathia-holoprosencephaly

Two stillborn sisters had characteristics of both agnathia and holoprosencephaly. Familial occurrence implies that agnathia-holoprosencephaly may be determined by a single recessive gene, something to be taken into account when counseling such families. Evidence from human experience and various animal models suggests that agnathia-holoprosencephaly represents a causally heterogeneous single developmental field defect. Anatomical studies of these two stillborn sisters support the view that they shared a developmental field defect which affected structures in the face, cranial cavity, and upper neck. The pathogenesis of these variably expressed defects probably relates to defects in neural crest cells of cranial origin and/or to underlying mesodermal support elements of these cells.

Cranial defects in the Goldenhar syndrome

Four patients are presented with the Goldenhar syndrome (GS) and cranial defects consisting of plagiocephaly, microcephaly, skull defects, or intracranial dermoid cysts. Twelve cases from the literature add hydrocephalus, encephalocele, and arhinencephaly to a growing list of brain anomalies in GS. As a group, these patients emphasize the variability of GS and the increased risk for developmental retardation with multiple, severe, or unusual manifestations. The temporal relation of proposed teratogenic events in GS provides an opportunity to reconstruct biological relationships within the 3-5-week human embryo.