Experimental aspects of the pathogenesis of Robin sequence

Tri-lobed Tongue: Rare Manifestation Accompany With Pierre Robin Sequence

BACKGROUND

The tongue is an essential organ accounted for proper deglutition and articulation. Surgical repair should be planned soon after diagnosis of any structural abnormality to prevent later speech and swallowing disorders. The lobulated tongue could be isolated (sporadic) or in association with other disorders. Pierre Robin Sequence (PRS) consists of the clinical trial of congenital micrognathia, glossoptosis, and airway obstruction with variable inclusion of a cleft palate. We present the case of a rare congenital tri-lobed tongue with Pierre Robin sequence and its surgical management in our hospital setting.

CASE PRESENTATION

Six-month-old boy presented with severe retrognathia, high arch, complete isolated cleft palate, and a bizarre mass in the oral cavity instead of his tongue that led to disruption of his swallowing. The mass (deformed tongue) check clearly, and the normal shape of the tongue was restored through multiple local randomized flaps. Dramatic improvement in swallowing was noticed 6 months after surgery during postoperative follow-up.

DISCUSSION

We present the case of a patient with a tri-lobed tongue with Pierre Robin sequence characterized by severe retrognathia, high arch, and complete isolated cleft palate. This seems to be the first reported case of this particular craniofacial anomaly.

CONCLUSION

The management of infants with the Pierre Robin sequence is complex, and much still needs to be learned and practiced. Congenital tri-lobed tongue with a cleft as part of the Pierre Robin sequence is a very rare malformation. Early repair of the tongue is important to assist the baby in adapting to speech and swallowing as they grow.

Phenotypes, Developmental Basis, and Genetics of Pierre Robin Complex

The phenotype currently accepted as Pierre Robin syndrome/sequence/anomalad/complex (PR) is characterized by mandibular dysmorphology, glossoptosis, respiratory obstruction, and in some cases, cleft palate. A causative sequence of developmental events is hypothesized for PR, but few clear causal relationships between discovered genetic variants, dysregulated gene expression, precise cellular processes, pathogenesis, and PR-associated anomalies are documented. This review presents the current understanding of PR phenotypes, the proposed pathogenetic processes underlying them, select genes associated with PR, and available animal models that could be used to better understand the genetic basis and phenotypic variation of PR.

Pierre Robin sequence: review of diagnostic and treatment challenges

Pierre Robin sequence is not a rare condition and paediatric specialists caring for respiratory related issues are likely to encounter cases in their practice. There have been a few recent reviews on the topic, mostly focusing on the surgical interventions performed for cases with severe airway obstruction. In the present review, we will highlight the different challenges that remain today in the global evaluation of infants afflicted with this condition through a thorough review of the medical literature, giving the clinician a full scope of the disease and of the various management options. The need for an improved objective evaluation of airway obstruction and for a better classification will be emphasized. We are therefore proposing a novel classification scheme that will better account for respiratory and feeding difficulties in these infants. Finally, many knowledge gaps persist regarding this condition, underlining the necessity for further research both in the genetic field and regarding the outcome of therapy.

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.

Familial dysautonomia model reveals Ikbkap deletion causes apoptosis of Pax3+ progenitors and peripheral neurons

Familial dysautonomia (FD) is a devastating developmental and progressive peripheral neuropathy caused by a mutation in the gene inhibitor of kappa B kinase complex-associated protein (IKBKAP). To identify the cellular and molecular mechanisms that cause FD, we generated mice in which Ikbkap expression is ablated in the peripheral nervous system and identify the steps in peripheral nervous system development that are Ikbkap-dependent. We show that Ikbkap is not required for trunk neural crest migration or pathfinding, nor for the formation of dorsal root or sympathetic ganglia, or the adrenal medulla. Instead, Ikbkap is essential for the second wave of neurogenesis during which the majority of tropomyosin-related kinase A (TrkA(+)) nociceptors and thermoreceptors arise. In its absence, approximately half the normal complement of TrkA(+) neurons are lost, which we show is partly due to p53-mediated premature differentiation and death of mitotically-active progenitors that express the paired-box gene Pax3 and give rise to the majority of TrkA(+) neurons. By the end of sensory development, the number of TrkC neurons is significantly increased, which may result from an increase in Runx3(+) cells. Furthermore, our data demonstrate that TrkA(+) (but not TrkC(+)) sensory and sympathetic neurons undergo exacerbated Caspase 3-mediated programmed cell death in the absence of Ikbkap and that this death is not due to a reduction in nerve growth factor synthesis. In summary, these data suggest that FD does not result from a failure in trunk neural crest migration, but rather from a critical function for Ikbkap in TrkA progenitors and TrkA(+) neurons.

Developmental and genetic perspectives on Pierre Robin sequence

Pierre Robin sequence (PRS) is a craniofacial anomaly comprising mandibular hypoplasia, cleft secondary palate and glossoptosis leading to life-threatening obstructive apnea and feeding difficulties during the neonatal period. The respiratory issues require careful management and in severe cases may require extended stays in neonatal intensive care units and surgical intervention such as lengthening the lower jaw or tracheotomy to relieve airway obstruction. These feeding and respiratory complications frequently continue well into childhood, affecting not only growth and development but also impacting on long term educational attainment. The diagnosis of PRS depends on readily recognizable clinical features but the phenotypic similarity of many PRS individuals conceals considerable etiological heterogeneity. Defects in the growth of the mandible sit at the core of PRS and the natural history of PRS can be classified into two major streams: primary defects of mandibular outgrowth and elongation and issues that are external to the mandibular skeleton but that secondarily impact on its growth. These altered developmental trajectories appear to be driven by a range of influences including defects in cartilage growth, neuromuscular function and fetal constraint. Various genetic and cytogenetic associations have been made with PRS and the diversity of these associations highlights the fact that there are numerous ways to arrive at this common phenotypic endpoint.

Upper airway changes in Pierre Robin sequence from childhood to adulthood

OBJECTIVES

To investigate pharyngeal airway changes in patients with Pierre Robin sequence (PRS) longitudinally from childhood to adulthood.

SETTING AND SAMPLE POPULATION

Cleft Lip and Palate Unit, Clinic of Orthodontics, University of Zurich. Twenty-four patients born between 1970 and 1990 with non-syndromic PRS.

MATERIALS AND METHODS

Lateral cephalograms at age 5 (T1), 10 (T2), 15 (T3) and 20 (T4) years were available. Variables describing pharyngeal airway dimensions, soft palate morphology, tongue and hyoid position, skeletal morphology and head posture were assessed.

RESULTS

A significant increase in nasopharyngeal depth was found over the entire observation period (T1 10.7 to T4 19.1 mm, p < 0.001), especially between T2 and T3 (change 3.8 mm, p < 0.001), and was mainly due to adenoid recession (r = -0.75, p < 0.001; variation explained by 56%). Increase in velopharyngeal depth mainly took place between T3 and T4 (change 2.3 mm, p < 0.01). It was due to more anterior tongue posture (r = 0.65, p < 0.001; 42.5% of variation explained), in turn allowing the soft palate to take a more vertical position (r = -0.52, p < 0.001). Increase in oropharyngeal depth was associated with head extension and anterior mandibular positioning (36% of variation explained). However, significance was not reached (T1 8.3 to T4 9.8 mm, p > 0.05).

CONCLUSIONS

Upper airway dimensions in children with PRS improve with time, except for the oropharyngeal airway. Despite large interindividual variation, the mean remained in the lower reaches of normality described in other studies. Thus, further research should investigate the prevalence of obstructive sleep apnoea in adults with PRS.

Genetics and management of the patient with orofacial cleft

Cleft lip or palate (CL/P) is a common facial defect present in 1 : 700 live births and results in substantial burden to patients. There are more than 500 CL/P syndromes described, the causes of which may be single-gene mutations, chromosomopathies, and exposure to teratogens. Part of the most prevalent syndromic CL/P has known etiology. Nonsyndromic CL/P, on the other hand, is a complex disorder, whose etiology is still poorly understood. Recent genome-wide association studies have contributed to the elucidation of the genetic causes, by raising reproducible susceptibility genetic variants; their etiopathogenic roles, however, are difficult to predict, as in the case of the chromosomal region 8q24, the most corroborated locus predisposing to nonsyndromic CL/P. Knowing the genetic causes of CL/P will directly impact the genetic counseling, by estimating precise recurrence risks, and the patient management, since the patient, followup may be partially influenced by their genetic background. This paper focuses on the genetic causes of important syndromic CL/P forms (van der Woude syndrome, 22q11 deletion syndrome, and Robin sequence-associated syndromes) and depicts the recent findings in nonsyndromic CL/P research, addressing issues in the conduct of the geneticist.

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.

Rare syndromes of the head and face-Pierre Robin sequence

Pierre Robin sequence (PRS) is an association of clinical features consisting of mandibular hypoplasia, cleft secondary palate, and glossoptosis leading to obstructive apnea and feeding difficulties. PRS can occur as an isolated condition or can be found in association with a range of other features in a number of conditions including Treacher collins and Stickler syndromes. The frequent association of the PRS triad suggests a common underlying developmental mechanism which impacts on each of these tissues. Isolated PRS is typically sporadic but when familial usually exhibits autosomal dominant inheritance. The term PRS is applied on the basis of the pattern of malformation rather than etiology and growing evidence indicates that the initiating genetic lesion is variable. Various chromosomal anomalies have been associated with PRS including loci on chromosomes 2, 4, and 17. Associations with genes including SOX9, a number of collagen genes and work with animal models suggest the phenotype derives from a cartilage defect during early facial growth. However, alternative theories have been proposed and these highlight the difficulty of characterising congenital anomalies of craniofacial development in which multiple etiologies can result in very similar phenotypes.

Microdeletion del(22)(q12.2) encompassing the facial development-associated gene, MN1 (meningioma 1) in a child with Pierre-Robin sequence (including cleft palate) and neurofibromatosis 2 (NF2): a case report and review of the literature

BACKGROUND

Pierre-Robin sequence (PRS) is defined by micro- and/or retrognathia, glossoptosis and cleft soft palate, either caused by deformational defect or part of a malformation syndrome. Neurofibromatosis type 2 (NF2) is an autosomal dominant syndrome caused by mutations in the NF2 gene on chromosome 22q12.2. NF2 is characterized by bilateral vestibular schwannomas, spinal cord schwannomas, meningiomas and ependymomas, and juvenile cataracts. To date, NF2 and PRS have not been described together in the same patient.

CASE PRESENTATION

We report a female with PRS (micrognathia, cleft palate), microcephaly, ocular hypertelorism, mental retardation and bilateral hearing loss, who at age 15 was also diagnosed with severe NF2 (bilateral cerebellopontine schwannomas and multiple extramedullary/intradural spine tumors). This is the first published report of an individual with both diagnosed PRS and NF2. High resolution karyotype revealed 46, XX, del(22)(q12.1q12.3), FISH confirmed a deletion encompassing NF2, and chromosomal microarray identified a 3,693 kb deletion encompassing multiple genes including NF2 and MN1 (meningioma 1).Five additional patients with craniofacial dysmorphism and deletion in chromosome 22-adjacent-to or containing NF2 were identified in PubMed and the DECIPHER clinical chromosomal database. Their shared chromosomal deletion encompassed MN1, PITPNB and TTC28. MN1, initially cloned from a patient with meningioma, is an oncogene in murine hematopoiesis and participates as a fusion gene (TEL/MN1) in human myeloid leukemias. Interestingly, Mn1-haploinsufficient mice have abnormal skull development and secondary cleft palate. Additionally, Mn1 regulates maturation and function of calvarial osteoblasts and is an upstream regulator of Tbx22, a gene associated with murine and human cleft palate. This suggests that deletion of MN1 in the six patients we describe may be causally linked to their cleft palates and/or craniofacial abnormalities.

CONCLUSIONS

Thus, our report describes a NF2-adjacent chromosome 22q12.2 deletion syndrome and is the first to report association of MN1 deletion with abnormal craniofacial development and/or cleft palate in humans.

The canonical Wnt signaling activator, R-spondin2, regulates craniofacial patterning and morphogenesis within the branchial arch through ectodermal-mesenchymal interaction

R-spondins are a recently characterized family of secreted proteins that activate Wnt/β-catenin signaling. Herein, we determine R-spondin2 (Rspo2) function in craniofacial development in mice. Mice lacking a functional Rspo2 gene exhibit craniofacial abnormalities such as mandibular hypoplasia, maxillary and mandibular skeletal deformation, and cleft palate. We found that loss of the mouse Rspo2 gene significantly disrupted Wnt/β-catenin signaling and gene expression within the first branchial arch (BA1). Rspo2, which is normally expressed in BA1 mesenchymal cells, regulates gene expression through a unique ectoderm-mesenchyme interaction loop. The Rspo2 protein, potentially in combination with ectoderm-derived Wnt ligands, up-regulates Msx1 and Msx2 expression within mesenchymal cells. In contrast, Rspo2 regulates expression of the Dlx5, Dlx6, and Hand2 genes in mesenchymal cells via inducing expression of their upstream activator, Endothelin1 (Edn1), within ectodermal cells. Loss of Rspo2 also causes increased cell apoptosis, especially within the aboral (or caudal) domain of the BA1, resulting in hypoplasia of the BA1. Severely reduced expression of Fgf8, a survival factor for mesenchymal cells, in the ectoderm of Rspo2(-/-) embryos is likely responsible for increased cell apoptosis. Additionally, we found that the cleft palate in Rspo2(-/-) mice is not associated with defects intrinsic to the palatal shelves. A possible cause of cleft palate is a delay of proper palatal shelf elevation that may result from the small mandible and a failure of lowering the tongue. Thus, our study identifies Rspo2 as a mesenchyme-derived factor that plays critical roles in regulating BA1 patterning and morphogenesis through ectodermal-mesenchymal interaction and a novel genetic factor for cleft palate.

Developmental aspects of the upper airway: report from an NHLBI Workshop, March 5-6, 2009

The upper airway serves three important functions: respiration, swallowing, and speech. During development it undergoes significant structural and functional changes that affect its size, shape, and mechanical properties. Abnormalities of the upper airway require prompt attention, because these often alter ventilatory patterns and gas exchange, particularly during sleep when upper airway motor tone and ventilatory drive are diminished. Recognizing the relationship of early life events to lung health and disease, the National Heart, Lung, and Blood Institute (NHLBI), with cofunding from the Office of Rare Diseases (ORD), convened a workshop of extramural experts, from many disciplines. The objective of the workshop was: (1) to review the state of science in pediatric upper airway disorders; (2) to make recommendations to the Institute to fill knowledge gaps; (3) to prioritize new research directions; and (4) to capitalize on scientific opportunities. This report provides recommendations that could facilitate translation of basic research findings into practice to better diagnose, treat, and prevent airway compromise in children.

Abnormal mandibular growth and the condylar cartilage

Deviations in the growth of the mandibular condyle can affect both the functional occlusion and the aesthetic appearance of the face. The reasons for these growth deviations are numerous and often entail complex sequences of malfunction at the cellular level. The aim of this review is to summarize recent progress in the understanding of pathological alterations occurring during childhood and adolescence that affect the temporomandibular joint (TMJ) and, hence, result in disorders of mandibular growth. Pathological conditions taken into account are subdivided into (1) congenital malformations with associated growth disorders, (2) primary growth disorders, and (3) acquired diseases or trauma with associated growth disorders. Among the congenital malformations, hemifacial microsomia (HFM) appears to be the principal syndrome entailing severe growth disturbances, whereas growth abnormalities occurring in conjunction with other craniofacial dysplasias seem far less prominent than could be anticipated based on their often disfiguring nature. Hemimandibular hyperplasia and elongation undoubtedly constitute the most obscure conditions that are associated with prominent, often unilateral, abnormalities of condylar, and mandibular growth. Finally, disturbances of mandibular growth as a result of juvenile idiopathic arthritis (JIA) and condylar fractures seem to be direct consequences of inflammatory and/or mechanical damage to the condylar cartilage.

Multiple functions of Snail family genes during palate development in mice

Palate development requires precise regulation of gene expression changes, morphogenetic movements and alterations in cell physiology. Defects in any of these processes can result in cleft palate, a common human birth defect. The Snail gene family encodes transcriptional repressors that play essential roles in the growth and patterning of vertebrate embryos. Here we report the functions of Snail (Snai1) and Slug (Snai2) genes during palate development in mice. Snai2(-/-) mice exhibit cleft palate, which is completely penetrant on a Snai1 heterozygous genetic background. Cleft palate in Snai1(+/-) Snai2(-/-) embryos is due to a failure of the elevated palatal shelves to fuse. Furthermore, while tissue-specific deletion of the Snai1 gene in neural crest cells does not cause any obvious defects, neural-crest-specific Snai1 deletion on a Snai2(-/-) genetic background results in multiple craniofacial defects, including a cleft palate phenotype distinct from that observed in Snai1(+/-) Snai2(-/-) embryos. In embryos with neural-crest-specific Snai1 deletion on a Snai2(-/-) background, palatal clefting results from a failure of Meckel's cartilage to extend the mandible and thereby allow the palatal shelves to elevate, defects similar to those seen in the Pierre Robin Sequence in humans.