Examining the genetics of congenital facial paralysis--a closer look at Moebius syndrome

Clinical and Genetic Correlation in Neurocristopathies: Bridging a Precision Medicine Gap

Neurocristopathies (NCPs) encompass a spectrum of disorders arising from issues during the formation and migration of neural crest cells (NCCs). NCCs undergo epithelial-mesenchymal transition (EMT) and upon key developmental gene deregulation, fetuses and neonates are prone to exhibit diverse manifestations depending on the affected area. These conditions are generally rare and often have a genetic basis, with many following Mendelian inheritance patterns, thus making them perfect candidates for precision medicine. Examples include cranial NCPs, like Goldenhar syndrome and Axenfeld-Rieger syndrome; cardiac-vagal NCPs, such as DiGeorge syndrome; truncal NCPs, like congenital central hypoventilation syndrome and Waardenburg syndrome; and enteric NCPs, such as Hirschsprung disease. Additionally, NCCs' migratory and differentiating nature makes their derivatives prone to tumors, with various cancer types categorized based on their NCC origin. Representative examples include schwannomas and pheochromocytomas. This review summarizes current knowledge of diseases arising from defects in NCCs' specification and highlights the potential of precision medicine to remedy a clinical phenotype by targeting the genotype, particularly important given that those affected are primarily infants and young children.

Moebius Syndrome: An Updated Review of Literature

Moebius Syndrome, is a rare, non-progressive congenital neuropathological syndrome characterized primarily by the underdevelopment of the facial (CN VII) and abducens nerve (CN VI). Other features of Moebius Syndrome include facial nerve paresis, ophthalmoplegias, orthodontic deficiencies (including crowded dentition, swollen and hyperplastic gingiva, dental calculus, etc.), musculoskeletal abnormalities, and impaired mental function. Due to the rarity of the disorder, very few case studies have been reported in the literature. This article summarizes the significant features of the disease according to commonalities in reported cases, along with several newly recognized features cited in recent literature. We have explored the different diagnostic criteria and the newly recognized imaging modalities that may be used. Understandably, the condition detrimentally affects a patient's quality of life; thus, treatment measures have also been outlined. This study aims to provide updated literature on Moebius Syndrome MBS and improve understanding of the condition.

Poland-Möbius syndrome: a case report implicating a novel mutation of the PLXND1 gene and literature review

BACKGROUND

Möbius (Moebius) and Poland's syndromes are two rare congenital syndromes characterized by non-progressive bilateral (and often asymmetric) dysfunction of the 6^th and 7^th cranial nerves and hypoplasia of the pectoral muscles associated with chest wall and upper limb anomalies respectively. Manifest simultaneously as Poland-Möbius (Poland-Moebius) syndrome, debate continues as to whether this is a distinct nosological entity or represents phenotypic variation as part of a spectrum of disorders of rhomboencephalic development. Etiological hypotheses implicate both genetic and environmental factors. The PLXND1 gene codes for a protein expressed in the fetal central nervous system and vascular endothelium and is thus involved in embryonic neurogenesis and vasculogenesis. It is located at chromosome region 3q21-q22, a locus of interest for Möbius syndrome.

CASE PRESENTATION

We present the first report of a patient with Poland-Möbius syndrome and a mutation in the PLXND1 gene. A child with Poland-Möbius syndrome and a maternally inherited missense variant (NM_015103.2:ex14:c.2890G > Ap.V964M) in the PLXND1 gene is described. In order to contextualize these findings, the literature was examined to identify other confirmed cases of Poland-Möbius syndrome for which genetic data were available. Fourteen additional cases of Poland-Möbius syndrome with genetic studies are described in the literature. None implicated the PLXND1 gene which has previously been implicated in isolated Möbius syndrome.

CONCLUSIONS

This report provides further evidence in support of a role for PLXND1 mutations in Möbius syndrome and reasserts the nosological link between Möbius and Poland's syndromes.

LEVEL OF EVIDENCE

Level V, Descriptive Study.

Zygomatic Muscle Neurotization with Nerve Grafts and End-to-Side Neurorrhaphies: A New Technique for Facial Palsy

Moebius syndrome is a rare congenital facial palsy that can generate serious emotional repercussions, mainly due to the inability to smile. Currently, no treatment is available; however, surgery can restore muscle function. This case report introduces a new technique for the treatment of Moebius syndrome with zygomatic muscle neurotization using nerve grafts and end-to-side neurorrhaphies, in a 3-year-old girl diagnosed with bilateral Moebius syndrome who was unable to smile on the left side. After 4 years, the patient presented with full smile restoration on the left side, with right and left independent movements and complete symmetry.

Dental management of a patient with Moebius syndrome: A case report

BACKGROUND

Moebius syndrome (MBS) is a nonprogressive and rare congenital neuromuscular disorder involving the facial nerve and abductor nerve; it mainly manifests as facial paralysis and eye strabismus paralytic symptoms. Tissues in the oral cavity are also compromised, characterized by microstomia, micrognathia, tongue malformation, cleft lip, high arched palate or cleft palate, bifid uvula, and dental malocclusion. Therefore, dentistry plays a fundamental and crucial role in caring for these individuals. However, there is limited available data on MBS treatment, particularly regarding dental management.

CASE SUMMARY

This case report presents dental treatment of a 21-year-old man with MBS and discusses crucial interactions among oral complications of MBS. In this case, the patient was clinically characterized by congenital neuromuscular disorder, occlusal disorders, and tooth and gum problems. It is noteworthy that the patient presented early eruption of deciduous teeth 2 mo after birth, which has not been reported in other MBS cases and suggests a potentially new clinical manifestation of this syndrome. It is important to note that MBS cannot be cured, and oral manifestations of this syndrome can be managed by a multidisciplinary health care team that helps the patient maintain oral hygiene and dental health. After a series of oral treatments, no obvious poor oral hygiene, swollen gums, or abnormal imaging results were observed after 2 years of follow-up.

CONCLUSION

This case addressed the oral clinical manifestations of MBS and difficulties experienced during dental management, and suggested early tooth eruption as a potentially new clinical manifestation of this syndrome. Knowledge of the loop-mediated association among oral complications of this syndrome is essential to perfecting treatments.

Moebius syndrome: Craniofacial clinical manifestations and their association with prenatal exposure to misoprostol

BACKGROUND

A growing link between prenatal exposure to misoprostol (PEM) and Moebius syndrome (MS) or sequence has been reported. Our objectives were to describe the craniofacial clinical manifestations associated with MS and to determine the frequency of PEM, comparing cases of exposure and nonexposure.

METHODS

A descriptive, cross-sectional study of 140 patients with MS. Clinical evaluations, as well as 140 interviews with mothers residing in 39 cities or districts of Colombia, were carried out between April 2008 and May 2018. Additionally, previous clinical history of each case was reviewed.

RESULTS

The average age of the patients with MS was 8.4 years (29 days to 48 years). All of them presented facial nerve involvement and abducens, 112 (80.8%) with bilateral facial paralysis. 98.5% presented craniofacial disorders, and there were no significant differences between those exposed and not exposed to misoprostol. Forty-seven percentage of patients (64 cases) presented PEM, in 98.4% of which abortion had been intended.

CONCLUSION

PEM could have an influence in the appearance of new cases of MS by increasing the frequency of bleeding during gestation, without increasing the number of associated craniofacial malformations. We present the biggest series on MS and craniofacial findings in the literature, along with a meaningful reference for its understanding.

LEVEL OF EVIDENCE

3b.

Multigenic truncation of the semaphorin-plexin pathway by a germline chromothriptic rearrangement associated with Moebius syndrome

Moebius syndrome (MBS) is a congenital disorder caused by paralysis of the facial and abducens nerves. Although a number of candidate genes have been suspected, so far only mutations in PLXND1 and REV3L are confirmed to cause MBS. Here, we fine mapped the breakpoints of a complex chromosomal rearrangement (CCR) 46,XY,t(7;8;11;13) in a patient with MBS, which revealed 41 clustered breakpoints with typical hallmarks of chromothripsis. Among 12 truncated protein-coding genes, SEMA3A is known to bind to the MBS-associated PLXND1. Intriguingly, the CCR also truncated PIK3CG, which in silico interacts with REVL3 encoded by the other known MBS-gene REV3L, and with the SEMA3A/PLXND1 complex via FLT1. Additional studies of other complex rearrangements may reveal whether the multiple breakpoints in germline chromothripsis may predispose to complex multigenic disorders.

Congenital facial palsy and emotion processing: The case of Moebius syndrome

According to the Darwinian perspective, facial expressions of emotions evolved to quickly communicate emotional states and would serve adaptive functions that promote social interactions. Embodied cognition theories suggest that we understand others' emotions by reproducing the perceived expression in our own facial musculature (facial mimicry) and the mere observation of a facial expression can evoke the corresponding emotion in the perceivers. Consequently, the inability to form facial expressions would affect the experience of emotional understanding. In this review, we aimed at providing account on the link between the lack of emotion production and the mechanisms of emotion processing. We address this issue by taking into account Moebius syndrome, a rare neurological disorder that primarily affects the muscles controlling facial expressions. Individuals with Moebius syndrome are born with facial paralysis and inability to form facial expressions. This makes them the ideal population to study whether facial mimicry is necessary for emotion understanding. Here, we discuss behavioral ambiguous/mixed results on emotion recognition deficits in Moebius syndrome suggesting the need to investigate further aspects of emotional processing such as the physiological responses associated with the emotional experience during developmental age.

Management of Bilateral Facial Palsy

Bilateral facial paralysis is a rare entity that occurs in both pediatric and adult patients and can have congenital or acquired causes. When paralysis does not resolve with conservative or medical management, surgical intervention may be indicated. This article presents the authors' preferred technique for facial reanimation in patients with bilateral congenital facial paralysis. Specifically, a staged bilateral segmental gracilis transfer to ipsilateral nerve to masseter is discussed.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

Bilateral Facial Paralysis: A 13-Year Experience

BACKGROUND

Bilateral facial palsy is a rare clinical entity caused by myriad disparate conditions requiring different treatment paradigms. Lyme disease, Guillain-Barré syndrome, and leukemia are several examples. In this article, the authors describe the cause, the initial diagnostic approach, and the management of long-term sequelae of bilateral paralysis that has evolved in the authors' center over the past 13 years.

METHODS

A chart review was performed to identify all patients diagnosed with bilateral paralysis at the authors' center between January of 2002 and January of 2015. Demographics, signs and symptoms, diagnosis, initial medical treatment, interventions for facial reanimation, and outcomes were reviewed.

RESULTS

Of the 2471 patients seen at the authors' center, 68 patients (3 percent) with bilateral facial paralysis were identified. Ten patients (15 percent) presented with bilateral facial paralysis caused by Lyme disease, nine (13 percent) with Möbius syndrome, nine (13 percent) with neurofibromatosis type 2, five (7 percent) with bilateral facial palsy caused by brain tumor, four (6 percent) with Melkersson-Rosenthal syndrome, three (4 percent) with bilateral temporal bone fractures, two (3 percent) with Guillain-Barré syndrome, one (2 percent) with central nervous system lymphoma, one (2 percent) with human immunodeficiency virus infection, and 24 (35 percent) with presumed Bell palsy. Treatment included pharmacologic therapy, physical therapy, chemodenervation, and surgical interventions.

CONCLUSIONS

Bilateral facial palsy is a rare medical condition, and treatment often requires a multidisciplinary approach. The authors outline diagnostic and therapeutic algorithms of a tertiary care center to provide clinicians with a systematic approach to managing these complicated patients.