Ophthalmologic and systemic features in möbius syndrome an italian case series

Through their eyes: Navigating life with limited eyelid closure in patients with Moebius syndrome

BACKGROUND

Moebius syndrome (MoS), a rare congenital condition caused by the underdevelopment of the sixth and seventh cranial nerves, presents with uni- or bilateral facial paralysis and lateral gaze palsy. Those with MoS often have incomplete eyelid closure (lagophthalmos). This study aimed to investigate the experiences of individuals living with incomplete eyelid closure due to MoS.

METHODS

Participants shared their experiences in semi-structured open-ended focus groups during the 2023 MoS Foundation Conference. Data were analyzed thematically using Nvivo. The Terzis and Bruno scoring system was used to grade participant eyelid closure (range: 1 being no eyelid closure with full scleral show to 5 being complete eyelid closure with no scleral show) and blink (from 1 being no blink to 5 being synchronous and complete blink present). Marginal reflex distances 1 and 2 (MRD1 and MRD2) were measured to grade for ptosis and lid retraction, respectively.

RESULTS

Fifteen participants participated in two focus groups, comprising adults (n = 12) and adolescents (n = 3). All participants had lagophthalmos with some scleral show, ptosis, and lid retraction. The median eyelid closure score was 3 (incomplete eye closure with 1/3 scleral showing). Five key themes were identified: social stigma and misunderstanding, daily life impacts, seasonal exacerbations, different attitudes toward surgical intervention between adults and adolescents, and a prevailing sense of self-acceptance regarding their condition.

CONCLUSION

Incomplete eyelid closure poses significant social challenges for individuals with MoS, especially around social encounters. Our findings show the importance of developing tailored communication tools to support those living with this facial difference.

Two novel compound heterozygous HOXB1 variants in congenital facial palsy: A case report and a brief review of the literature

Hereditary congenital facial palsy (HCFP) is a medical condition caused by dysfunction of the seventh cranial nerve. HCFP is characterized by feeding difficulties and dysmorphic features in the orofacial region. In some cases hearing loss, strabismus, limb malformations, and musculoskeletal defects may be associated. There are three types of HCFP: HCFP3 (OMIM 614744) results from autosomal recessive pathogenic variants in the HOXB1 gene, while HCFP1 and 2 (OMIM 601471, 604185) are autosomal dominant, genetically less defined conditions. We report on a case of congenital bilateral facial palsy due to two novel compound heterozygous variants in the HOXB1 gene, found by exome sequencing (ES), in a child with facial nerve axonal neuropathy without evidence of nerve hypoplasia on neuroimaging. The results of this report suggest that in individuals with congenital facial paralysis and preserved ocular motor skills, with or without facial nerve hypoplasia and with confirmed facial nerve axonal neuropathy, HOXB1 variants and therefore a diagnosis of HCFP3 should be primarily considered.

Long-term results of strabismus surgery for treatment of esotropia in patients with Möbius syndrome

PURPOSE

To evaluate the surgical results of Möbius syndrome esotropia following bilateral medial rectus recession with and without bilateral Hummelsheim procedure.

METHODS

The medical records of patients with Möbius syndrome operated on by a single surgeon from 1993 to 2022 were studied retrospectively. For each patient, age, sex, and ocular deviation before and after surgery were retrieved. Success was defined as a horizontal deviation of up to 15Δ and vertical deviation of <10Δ.

RESULTS

Eleven patients were included. Average patient age at the time of surgery was 4 years. Eight patients with esodeviation up to 70Δ underwent bilateral medial rectus recession; 3 patients with esotropia >70Δ underwent recession plus bilateral Hummelsheim procedure. The mean esodeviation before surgery was 52.5Δ in the first group and 86.6Δ in the second group. The mean horizontal deviation at early follow-up was esotropia of 7.4Δ in the first group and of 15Δ in the second group. The early success rate was 87% in the first group and 67% in the second group. Long-term follow-up revealed exoshift in 43% of the patients in the first group and all 3 patients in the second group.

CONCLUSIONS

In our small patient cohort of patients with Möbius syndrome, bilateral medial rectus recession corrected esodeviations of up to 70Δ. In more severe cases (>70Δ), adding bilateral Hummelsheim procedure was beneficial.

Etiologies, periocular manifestations and surgeries for congenital and childhood acquired facial nerve palsy

AIM

To report periocular surgeries performed for patients with congenital and childhood acquired facial nerve palsy (FNP).

METHODS

A retrospective case series of pediatric patients who presented with FNP over the last 34 years, was conducted at two tertiary eye hospitals in Riyadh. Data were collected from electronic charts, hospital records and external photos. Main outcome measures were visual acuity, lagophthalmos, eyelid abnormalities, Bell's phenomena, exposure keratopathy, and corneal scar; in these cases, periocular surgeries were required.

RESULTS

Among the 90 recruited subjects; the mean age of onset was 4.8±5.4 years old (range, 0.01 to 17.76 years). Traumatic and congenital causes of FNP were the most common, representing over 80% of the cases. Seventy-one patients developed lagophthalmos, 26 with severe exposure that resulted in scarring. Thirty-six (40%) cases had associated strabismus. Lower lid retraction was the most common eyelid abnormality noted in 23 cases, followed by entropion in 16 and ectropion in 6 cases. Temporary tarsorrhaphy was performed in three patients (3.3%), while 18 patients (20%) needed permanent tarsorrhaphy. Gold weight implants were placed in 17 patients (18.9%). Lower lid retraction repair was performed in twelve patients (13.3%). Five patients (5.6%) underwent lower eyelid entropion repair, and three patients (3.3%) underwent lower eyelid ectropion repair.

CONCLUSIONS

Lagophthalmos is the most common finding in children presenting with FNP and needs to be managed early to prevent permanent visual loss. Compared to adults, children may present with a different spectrum of eyelid abnormalities, with lower lid retraction and entropion being the most common eyelid malpositions.

Echoencephalography of Möbius sequence: A congenital cranial dysinnervation disorder with brainstem calcifications

BACKGROUND AND PURPOSE

Möbius sequence (MBS) previously known as Möbius syndrome is a rare nonprogressive developmental defect of the rhombencephalon leading to congenital abducens (VIth) and facial (VIIth) nerve palsy. Echoencephalography is the first, safe, noninvasive, and cost-effective imaging modality available at bedside. No study on the use of echoencephalography in neonates for the diagnosis of MBS has been previously reported.

METHODS

In this single tertiary center study, more than 18,000 neonates underwent echoencephalographic imaging over the span of two decades. Imaging was performed through the anterior, posterior, and lambdoid fontanelles. All neonates found to have calcifications of brainstem tegmental nuclei underwent additional imaging studies. Each neonate with MBS was carefully examined by the same investigator.

RESULTS

Five neonates were shown to have punctate, bilateral, symmetrical tegmental pontine calcifications through all three acoustic windows. These calcifications extended caudally in most patients, and rostrally in 2 patients. Brainstem hypoplasia was best seen through the posterior fontanelle. Three out of five infants were noted to have brainstem hypoplasia with straightening of the floor of the fourth ventricle. In two children, facial collicular bulges and hypoglossal eminences were present. All five infants fulfilled clinical diagnostic criteria of MBS. In addition, a wide array of cerebral defects is identified. Echoencephalographic findings were confirmed by other imaging modalities.

CONCLUSION

Knowledge of echoencephalographic features of MBS should improve its early recognition. A detailed description of the various imaging phenotypes of MBS is necessary to characterize the etiology of this heterogeneous congenital cranial dysinnervation disorder.

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.

Impact of Adding Augmented Superior Rectus Transpositions to Medial Rectus Muscle Recessions When Treating Esotropic Moebius Syndrome

PURPOSE

To describe outcomes after treatment of Moebius syndrome (MBS) esotropia by adjustable bilateral medial rectus recession (BMR) with and without augmented superior rectus transposition (SRT).

DESIGN

Retrospective case series.

METHODS

Patients meeting 2014 diagnostic criteria for MBS and treated at Boston Children's Hospital between 2003 and 2019 were identified via billing records and chart review. Visual acuity, sensorimotor evaluations, strabismus procedures, and other clinical features were recorded. Surgical outcomes for patients treated with strabismus surgery (excluding those with prior surgery elsewhere) were evaluated. The primary outcome measure was postoperative alignment comparing treatment by adjustable BMR vs adjustable BMR+SRT.

RESULTS

A total of 20 patients had MBS, and 12 of these (60%) were male. Fifteen patients (75%) had primary position esotropia, and all had bilateral abduction deficit. Eight of 20 patients met inclusion criteria for primary strabismus surgery outcome. Five had undergone adjustable BMR ranging from 4.5 to 6.5 mm. Three had undergone adjustable BMR+SRT, all with 4-mm medial rectus muscle recessions. Mean preoperative esotropia before treatment by BMR was 39.5 PD (± 15 PD) with mean postoperative esotropia 9 PD (± 7.9 PD) at 6 months. Mean preoperative esotropia before treatment by BMR+SRT was 70.8 PD (± 5.9 PD) with mean postoperative esotropia 2.5 PD (± 3.5 PD) at 6 months. Significantly greater reduction in esotropia resulted from BMR+SRT than from BMR (P = .036).

CONCLUSIONS

BMR proved sufficient to treat esotropia <50 PD and BMR+SRT for greater esotropia in patients with MBS-associated abduction limitation.

Shifting attention in visuospatial short-term memory does not require oculomotor planning: Insight from congenital gaze paralysis

Attention allows pieces of information stored in visuospatial short-term memory (VSSTM) to be selectively processed. Previous studies showed that shifts of attention in VSSTM in response to a retro-cue are accompanied by eye movements in the direction of the position of the memorized item although there is nothing left to look at. This finding raises the possibility that shifts of attention in VSSTM are underpinned by mechanisms originally involved in the planning and control of eye movements. To explore this possibility, we investigated the ability of an individual with congenital horizontal gaze paralysis (HGP2) to shift her attention horizontally or vertically toward a memorized item within VSSTM using a retro-cue paradigm. As efficient oculomotor programming is not innate but requires some trial and error learning and adaptation to develop, congenital paralysis prevents this development. Consequently, if shifts of attention in VSSTM rely on the same mechanisms as those supporting the programming of eye movements, then horizontal congenital gaze paralysis should necessarily prevent typical retro-cueing effect in the paralyzed axis. At odds with this prediction, HGP2 showed a typical retro-cueing effect in her paralyzed axis. This original finding indicates that selecting an item within VSSTM does not depend on the ability to program a saccade.

The epidemiology of Moebius syndrome in Italy

Background

The epidemiology of Moebius syndrome (MBS) is difficult to assess. In the present study, we investigated the epidemiology of MBS in a well-defined population within a precise geographical area.

Materials and methods

Our university hospital is the only national referral center for the diagnosis and treatment of MBS. Participants in this cross-sectional study were patients affected by MBS who had been periodically followed by our medical staff since 1998. Most of the patients were referred to our hospital by the Italian Association of Moebius Syndrome (AISMO). Demographic data necessary for study purposes were made available in the AISMO database, updated to April 2018. Subjects were assigned to geographical macroareas that are conventionally used in surveys and epidemiological investigations by the Italian National Institute of Statistics. The rates and prevalence of MBS cases were calculated on the basis of the last available survey of the Italian population. Each study parameter was then calculated with reference to the whole country and macroarea partition. The sex rate and the corresponding prevalence were calculated with respect to the weighted whole population and to the respective sex population. Chi-square analysis was adopted to investigate possible differences among geographical regions and/or sexes. A p value < 0.05 was considered statistically significant.

Results

One hundred and sixty-four out of 212 MBS patients fulfilled our inclusion criteria. All cases occurred in Caucasian patients and were sporadic. The median age at diagnosis was 3.6 years, ranging from 0 to 55 years; this range was significantly reduced to 0–5 years (median age at diagnosis: 2.2 years) in patients included after 2007. The calculated prevalence at birth was 0.06 cases per 10,000 live births, with an overall prevalence of 0.27/100,000, without any sex or geographical predominance.

Conclusions

The prevalence of MBS observed herein, rounded for possible underestimation, was 0.3/100,000 people, without any regional difference in the distribution of cases. Our data confirm the rarity of the disease on a national level.

Differentiating Moebius syndrome and other congenital facial weakness disorders with electrodiagnostic studies

INTRODUCTION

Congenital facial weakness (CFW) can result from facial nerve paresis with or without other cranial nerve and systemic involvement, or generalized neuropathic and myopathic disorders. Moebius syndrome is one type of CFW. In this study we explored the utility of electrodiagnostic studies (EDx) in the evaluation of individuals with CFW.

METHODS

Forty-three subjects enrolled prospectively into a dedicated clinical protocol and had EDx evaluations, including blink reflex and facial and peripheral nerve conduction studies, with optional needle electromyography.

RESULTS

MBS and hereditary congenital facial paresis (HCFP) subjects had low-amplitude cranial nerve 7 responses without other neuropathic or myopathic findings. Carriers of specific pathogenic variants in TUBB3 had, in addition, a generalized sensorimotor axonal polyneuropathy with demyelinating features. Myopathic findings were detected in individuals with Carey-Fineman-Ziter syndrome, myotonic dystrophy, other undefined myopathies, or CFW with arthrogryposis, ophthalmoplegia, and other system involvement.

DISCUSSION

EDx in CFW subjects can assist in characterizing the underlying pathogenesis, as well as guide diagnosis and genetic counseling.

Typically Efficient Lipreading without Motor Simulation

All it takes is a face-to-face conversation in a noisy environment to realize that viewing a speaker's lip movements contributes to speech comprehension. What are the processes underlying the perception and interpretation of visual speech? Brain areas that control speech production are also recruited during lipreading. This finding raises the possibility that lipreading may be supported, at least to some extent, by a covert unconscious imitation of the observed speech movements in the observer's own speech motor system-a motor simulation. However, whether, and if so to what extent, motor simulation contributes to visual speech interpretation remains unclear. In two experiments, we found that several participants with congenital facial paralysis were as good at lipreading as the control population and performed these tasks in a way that is qualitatively similar to the controls despite severely reduced or even completely absent lip motor representations. Although it remains an open question whether this conclusion generalizes to other experimental conditions and to typically developed participants, these findings considerably narrow the space of hypothesis for a role of motor simulation in lipreading. Beyond its theoretical significance in the field of speech perception, this finding also calls for a re-examination of the more general hypothesis that motor simulation underlies action perception and interpretation developed in the frameworks of motor simulation and mirror neuron hypotheses.

Efficient recognition of facial expressions does not require motor simulation

What mechanisms underlie facial expression recognition? A popular hypothesis holds that efficient facial expression recognition cannot be achieved by visual analysis alone but additionally requires a mechanism of motor simulation — an unconscious, covert imitation of the observed facial postures and movements. Here, we first discuss why this hypothesis does not necessarily follow from extant empirical evidence. Next, we report experimental evidence against the central premise of this view: we demonstrate that individuals can achieve normotypical efficient facial expression recognition despite a congenital absence of relevant facial motor representations and, therefore, unaided by motor simulation. This underscores the need to reconsider the role of motor simulation in facial expression recognition.

Brain phenotyping in Moebius syndrome and other congenital facial weakness disorders by diffusion MRI morphometry

In this study, we used a novel imaging technique, DTI (diffusion tensor imaging)-driven tensor-based morphometry, to investigate brain anatomy in subjects diagnosed with Moebius syndrome (n = 21), other congenital facial weakness disorders (n = 9) and healthy controls (n = 15). First, we selected a subgroup of subjects who satisfied the minimum diagnostic criteria for Moebius syndrome with only mild additional neurological findings. Compared to controls, in this cohort, we found a small region of highly significant volumetric reduction in the paramedian pontine reticular formation and the medial longitudinal fasciculus, important structures for the initiation and coordination of conjugate horizontal gaze. Subsequently, we tested if volume measurements from this region could help differentiate individual subjects of the different cohorts that were included in our study. We found that this region allowed discriminating Moebius syndrome subjects from congenital facial weakness disorders and healthy controls with high sensitivity (94%) and specificity (89%). Interestingly, this region was normal in congenital facial weakness subjects with oculomotor deficits of myopathic origin, who would have been classified as Moebius on the basis of purely clinical diagnostic criteria, indicating a potential role for diffusion MRI morphometry for differential diagnosis in this condition. When the entire Moebius syndrome cohort was compared to healthy controls, in addition to this 'landmark' region, other areas of significantly reduced volume in the brainstem emerged, including the location of the nuclei and fibres of cranial nerve VI (abducens nerve), and fibres of cranial nerve VII (facial nerve), and a more rostral portion of the medial longitudinal fasciculus. The high sensitivity and specificity of DTI-driven tensor-based morphometry in reliably detecting very small areas of volumetric abnormality found in this study suggest broader applications of this analysis in personalized medicine to detect hypoplasia or atrophy of small pathways and/or brainstem nuclei in other neurological disorders.

Long-term outcomes of strabismus surgery in Mobius sequence

Purpose: Mobius sequence is a rare disorder that results from underdevelopment of the sixth and seventh cranial nerves, with subsequent facial weakness and impairment of ocular abduction. Approximately half of the affected patients have esotropia with limitation of extraocular movements. This study retrospectively reviews the long-term outcome of strabismus surgery for such patients. Methods: The long-term follow-up results in five children with Mobius sequence, who were observed after strabismus surgery for congenital esotropia, were analyzed. Results: All patients had a limitation of abduction in both eyes. Preoperative esotropia ranged from 20 to 30 prism diopters (PD) (mean 27 PD). Patient age at surgery ranged from 4.5 to 14 months. Bilateral medial rectus muscle recession was performed in all cases, ranging from 4.0 to 6.5 mm. Inferior transposition of the medial rectus muscles was performed in two patients for treatment of V-pattern, and two patients also had surgery for vertical strabismus. Follow-up ranged from 4 to 19.5 years (mean 11.7 years). The final horizontal alignment was <8 PD in all patients, and all demonstrated some binocularity. Conclusion: Bilateral medial rectus muscle recession is an effective treatment for esotropia associated with Mobius sequence, with good long-term stability.

Autonomic Responses to Emotional Stimuli in Children Affected by Facial Palsy: The Case of Moebius Syndrome

According to embodied simulation theories, others' emotions are recognized by the unconscious mimicking of observed facial expressions, which requires the implicit activation of the motor programs that produce a specific expression. Motor responses performed during the expression of a given emotion are hypothesized to be directly linked to autonomic responses associated with that emotional behavior. We tested this hypothesis in 9 children (M_age = 5.66) affected by Moebius syndrome (MBS) and 15 control children (M_age = 6.6). MBS is a neurological congenital disorder characterized by underdevelopment of the VI and VII cranial nerves, which results in paralysis of the face. Moebius patients' inability to produce facial expressions impairs their capacity to communicate emotions through the face. We therefore assessed Moebius children's autonomic response to emotional stimuli (video cartoons) by means of functional infrared thermal (fIRT) imaging. Patients showed weaker temperature changes compared to controls, suggesting impaired autonomic activity. They also showed difficulties in recognizing facial emotions from static illustrations. These findings reveal that the impairment of facial movement attenuates the intensity of emotional experience, probably through the diminished activation of autonomic responses associated with emotional stimuli. The current study is the first to investigate emotional responses in MBS children, providing important insights into the role of facial expressions in emotional processing during early development.

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.

Will the real Moebius syndrome please stand up? A systematic review of the literature and statistical cluster analysis of clinical features

Moebius syndrome is a highly variable syndrome with abducens and facial nerve palsy as core features. Strict diagnostic criteria do not exist and the inconsistency of the associated features makes determination difficult. To determine what features are associated with Moebius syndrome we performed a systematic literature review resulting in a composite case series of 449 individuals labeled with Moebius syndrome. We applied minimum criteria (facial and abducens palsy) to determine the prevalence of associated clinical features in this series. Additionally, we performed statistical cluster analysis to determine which features tended to occur together. Our study comprises the largest series of patients with Moebius syndrome and the first to apply statistical methodology to elucidate clinical relationships. We present evidence for two groups within the Moebius diagnosis. Type 1: exhibiting micrognathia, limb anomalies and feeding/swallowing difficulty that tend to occur together. Type 2: phenotypically diverse but more associated with radiologically detectable neurologic abnormalities and developmental delay.

Pre- and Postsurgical Orthodontics in Patients with Moebius Syndrome

The authors report a combined orthodontic-surgical correction of an adult patient's malocclusion affected by Moebius Syndrome (MS). The treatment was conducted at the Dentistry Unit and the Maxillofacial Surgery Unit of the University Hospital of Parma. Treatment of malocclusion was performed after the correction of facial mimic mobility with smile surgery. The postoperative stability and orthodontic results were good and the correction of the morphological problems related to the syndrome was very satisfactory.

Three Cases of Exotropic Moebius Syndrome

Moebius syndrome is characterized by congenital facial palsy and limitation in horizontal gaze. The surgical results of the exotropic pattern are rare and have not been published before. The authors report three cases of exotropic Moebius syndrome. Maximal weakening of the lateral rectus muscles followed by strengthening of the medial recti in exotropic Moebius syndrome can improve exotropia significantly. Most of these cases also need some measures to relieve the often associated severe dry eye. [J Pediatr Ophthalmol Strabismus. 2017;54:e9-e12.].

Moebius syndrome: clinical features, diagnosis, management and early intervention

Background

Moebius syndrome (MBS) is rare disease characterized by nonprogressive congenital uni- or bi-lateral facial (i. e. VII cranial nerve) and abducens (i. e. VI cranial nerve) palsy. Although the neurological and ophthalmological findings are quite well-known, data concerning the attendant functional difficulties and their changes over time are seldom addressed.

In this study we attempt to estimate the prevalence of clinical and functional data in an Italian cohort affected by MBS.

Methods

The study included 50 children, 21 males and 29 females, aged 1 month to 14 years. The patients entered into a multidisciplinary diagnostic and follow-up protocol that had the specific purpose of detecting clinical and developmental deficits related to MBS.

Results

Involvement of the VII cranial nerve (total/partial, bilateral or unilateral) was present in 96 % of patients, and of the VI nerve in 85 %. Two patients were without impairment of the VII nerve and seven patients had no involvement of the VI nerve and were thus classified as Moebius-like because of the involvement of other CNs. Additional affected CNs were numbers III-IV in 16 %, V in 11 %, VIII and X each in 8 %, the XI in 6 %, the IX, most often partially, in 22 %, and the XII in 48 % of cases. Their development was characterized by global delay at one year of age, motor, emotional and speech difficulties at two years of age, a trend toward normalization at three years of age but with weakness in hand-eye coordination, and achieving average results at five years of age. Overall 90 % of children had a normal developmental quotient whereas only 10 % manifested cognitive deficits.

Conclusion

Early rehabilitation may enhance the recovery of normal function, particularly in vulnerable areas of development. It is possible that early intervention that integrates sensory and visual information with emotional difficulties can improve the prognosis of the child with MBS.

Homozygous HOXB1 loss-of-function mutation in a large family with hereditary congenital facial paresis

Hereditary congenital facial paresis (HCFP) belongs to the congenital cranial dysinnervation disorders. HCFP is characterized by the isolated dysfunction of the seventh cranial nerve and can be associated with hearing loss, strabismus, and orofacial anomalies. Möbius syndrome shares facial palsy with HCFP, but is additionally characterized by limited abduction of the eye(s). Genetic heterogeneity has been documented for HCFP as one locus mapped to chromosome 3q21-q22 (HCFP1) and a second to 10q21.3-q22.1 (HCFP2). The only known causative gene for HCFP is HOXB1 (17q21; HCFP3), encoding a homeodomain-containing transcription factor of the HOX gene family, which are master regulators of early developmental processes. The previously reported HOXB1 mutations change arginine 207 to another residue in the homeodomain and alter binding capacity of HOXB1 for transcriptional co-regulators and DNA. We performed whole exome sequencing in HCFP-affected individuals of a large consanguineous Moroccan family. The homozygous nonsense variant c.66C>G/p.(Tyr22*) in HOXB1 was identified in the four patients with HCFP and ear malformations, while healthy family members carried the mutation in the heterozygous state. This is the first disease-associated HOXB1 mutation with a likely loss-of-function effect suggesting that all HOXB1 variants reported so far also have severe impact on activity of this transcriptional regulator. © 2016 Wiley Periodicals, Inc.

De novo mutations in PLXND1 and REV3L cause Möbius syndrome

Möbius syndrome (MBS) is a neurological disorder that is characterized by paralysis of the facial nerves and variable other congenital anomalies. The aetiology of this syndrome has been enigmatic since the initial descriptions by von Graefe in 1880 and by Möbius in 1888, and it has been debated for decades whether MBS has a genetic or a non-genetic aetiology. Here, we report de novo mutations affecting two genes, PLXND1 and REV3L in MBS patients. PLXND1 and REV3L represent totally unrelated pathways involved in hindbrain development: neural migration and DNA translesion synthesis, essential for the replication of endogenously damaged DNA, respectively. Interestingly, analysis of Plxnd1 and Rev3l mutant mice shows that disruption of these separate pathways converge at the facial branchiomotor nucleus, affecting either motoneuron migration or proliferation. The finding that PLXND1 and REV3L mutations are responsible for a proportion of MBS patients suggests that de novo mutations in other genes might account for other MBS patients.

lt has been debated for decades if there is a genetic aetiology underlying Möbius syndrome, a neurological disorder characterized by facial paralysis. Here Tomas-Roca et al. use exome sequencing and identify de novo mutations in PLXND1 and REV3L, representing converging pathways in hindbrain development.

The genetic basis of incomitant strabismus: consolidation of the current knowledge of the genetic foundations of disease

In recent years, our understanding of the genetic foundations of incomitant strabismus has grown significantly. Much new understanding has been gleaned since the concept of congenital cranial dysinnervation disorders (CCDDs) was introduced in 2002, and the genetic basis of CCDDs continues to be elucidated. In this review, we aim to provide an update of the genetic and clinical presentation of these disorders. Disorders reviewed include Duane syndrome (DS), HOXA1 and HOXB1 syndromes, Moebius syndrome, congenital fibrosis of the extraocular muscles (CFEOM), and horizontal gaze palsy with progressive scoliosis (HGPPS).

Diagnostic distinctions and genetic analysis of patients diagnosed with moebius syndrome

OBJECTIVE

To improve diagnostic assessment in Moebius syndrome by (1) creating more selective diagnostic subgroups and (2) conducting genetic evaluation in a large patient cohort.

DESIGN

Prospective, observational study.

PARTICIPANTS

Attendees of 3 consecutive Moebius syndrome conferences held in the United States, with a prior diagnosis of Moebius syndrome, were invited to participate.

METHODS

Participants underwent standardized ophthalmologic examination for Moebius syndrome minimum diagnostic criteria (MDC) (congenital, nonprogressive facial palsy, and abduction deficit) and genetic testing for HOXA1, HOXB1, and TUBB3 mutations.

MAIN OUTCOME MEASURES

The number of patients meeting MDC and the number of patients with confirmed genetic mutation.

RESULTS

A total of 112 participants from 107 families enrolled. Nineteen percent of participants (21/112) did not meet accepted MDC for Moebius syndrome because they had abduction deficits without facial palsy or facial palsy with full ocular motility. All 5 families with 2 affected individuals had at least 1 family member in this category, including 2 siblings with comitant strabismus who harbored a HOXB1 mutation. Four unrelated participants, also not meeting MDC, had large-angle exotropia, vertical gaze deficiency, and ptosis consistent with congenital fibrosis of the extraocular muscles type 3 (CFEOM3); 1 patient harbored a novel TUBB3 mutation, and 3 patients harbored previously reported de novo TUBB3 mutations. Three percent of participants (3/112) met MDC but also had restricted vertical gaze. The remaining 88 participants (79%) met MDC and had full vertical gaze. This group had relatively homogeneous findings, and none had a family history of Moebius syndrome. Two previously undescribed phenomena were observed in this category: (1) volitional Bell's phenomenon and (2) intorsion with fixation.

CONCLUSIONS

Although the genetic contributors to classic Moebius syndrome remain elusive, accuracy in clinical evaluation will properly subdivide patients to facilitate genetic testing as new candidate genes are identified. Failure to test ocular motility may lead to misdiagnosis of Moebius syndrome, especially in patients who have facial palsy with full ductions. Patients with exotropia, vertical gaze limitation, and ptosis do not have classic Moebius syndrome and may have TUBB3 mutations associated with CFEOM3. To optimize genetic analysis, we propose adding "full vertical motility" to the MDC for Moebius syndrome.

Characterization of ocular motor deficits in congenital facial weakness: Moebius and related syndromes

Congenital facial weakness is present in a heterogeneous group of conditions. Among them is Moebius syndrome, which has been defined as a disorder with congenital, non-progressive facial weakness and limited abduction of one or both eyes. It is typically attributed to agenesis of the abducens and facial cranial nerves. This paper details ocular motor findings of 40 subjects (23 months to 64 years; 24 females, 16 males) with congenital facial weakness: 38 presented at a Moebius Syndrome Conference and two were clinic patients. A new classification scheme of patterns based on ocular motor phenotype is presented. Of 40 subjects, 37 had bilateral and three had unilateral facial weakness. The most common ocular motor pattern (Pattern 1, n=17, 43%) was bilateral horizontal gaze palsy with intact vertical range. Pattern 2 (n=10, 26%) was bilateral horizontal gaze palsy with variable vertical limitations. Pattern 3, which was rare, was isolated abduction deficits (n=2, 5%). Others had full motility range and did not meet minimal criteria for the diagnosis of Moebius syndrome (Pattern 4, n=10, 26%). One subject was too severely affected to characterize. Abnormal vertical smooth pursuit was present in 17 (57%) of 30 subjects: nine with Pattern 1, five with Pattern 2, and three with Pattern 4. Abnormal vertical saccades were present in 10 (34%) of 29 subjects. Vertical saccades appeared slow in nine: six with Pattern 1 and three with Pattern 2. Vertical saccades were absent in one subject with Pattern 2. Abnormal vertical optokinetic nystagmus was present in 19 (68%) of 28 subjects: 10 with Pattern 1, six with Pattern 2, one with Pattern 3, and two with Pattern 4. Reduced convergence was present in 19 (66%) of 29 subjects: nine with Pattern 1, six with Pattern 2, one with Pattern 3, and three with Pattern 4. The most common pattern of ocular motor deficit in Moebius syndrome is bilateral horizontal gaze palsy from pontine abducens nuclear defects, rather than abducens nerve involvement. Defects in the range or dynamic properties of vertical movements in subjects with congenital facial weakness may suggest involvement of ocular motor structures in the midbrain, including oculomotor nerves or nuclei, vertical supranuclear saccadic centres, and convergence neurons. Such deficits were found even in subjects with full vertical motility range. Classification of patterns of ocular motor deficits in congenital facial weakness may assist with further delineation of anatomic localization and identification of genetic deficits underlying these disorders.