Knockout of myomaker results in defective myoblast fusion, reduced muscle growth and increased adipocyte infiltration in zebrafish skeletal muscle

The fusion of myoblasts into multinucleated muscle fibers is vital to skeletal muscle development, maintenance and regeneration. Genetic mutations in the Myomaker (mymk) gene cause Carey-Fineman-Ziter syndrome (CFZS) in human populations. To study the regulation of mymk gene expression and function, we generated three mymk mutant alleles in zebrafish using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology and analyzed the effects of mymk knockout on muscle development and growth. Our studies demonstrated that knockout of mymk resulted in defective myoblast fusion in zebrafish embryos and increased mortality at larval stage around 35-45 days post-fertilization. The viable homozygous mutants were smaller in size and weighed approximately one-third the weight of the wild type (WT) sibling at 3 months old. The homozygous mutants showed craniofacial deformities, resembling the facial defect observed in human populations with CFZS. Histological analysis revealed that skeletal muscles of mymk mutants contained mainly small-size fibers and substantial intramuscular adipocyte infiltration. Single fiber analysis revealed that myofibers in mymk mutant were predominantly single-nucleated fibers. However, myofibers with multiple myonuclei were observed, although the number of nuclei per fiber was much less compared with that in WT fibers. Overexpression of sonic Hedgehog inhibited mymk expression in zebrafish embryos and blocked myoblast fusion. Collectively, these studies demonstrated that mymk is essential for myoblast fusion during muscle development and growth.

Moebius Syndrome: Measures of Observer Intelligibility with versus without Visual Cues in Bilateral Facial Paralysis

Objective:

This study investigated observers’ intelligibility for the spoken output of an individual with Moebius syndrome (MoS) with and without visual cues.

Design:

An audiovisual recording of the speaker's output was obtained for 50 Speech Intelligibility in Noise sentences consisting of 25 high predictability and 25 low predictability sentences. Stimuli were presented to observers under two conditions: audiovisual and audio only. Data were analyzed using a multivariate repeated measures model.

Observers:

Twenty students and faculty affiliated with the Department of Speech Pathology and Audiology at the University of Nevada, Reno.

Results:

ANOVA mixed design revealed that intelligibility for the audio condition only was significantly greater than intelligibility for the audiovisual condition; and accuracy for high predictability sentences was significantly greater than accuracy for low predictability sentences.

Conclusions:

The compensatory substitutional placements for phonemes produced by MoS speakers may detract from the intelligibility of speech. This is similar to the McGurk-MacDonald effect, whereby an illusory auditory signal is perceived when visual information from lip movements does not match the auditory information from speech. It also suggests that observers use contextual clues, more than the acoustic signal alone, to arrive at the accurate recognition of the message of the speakers with MoS. Therefore, speakers with MoS should be counseled in the top-down approach of auditory closure. When the speech signal is degraded, predictable messages are more easily understood than unpredictable ones. It is also important to confirm the speaking partner's understanding of the topic before proceeding.

Moebius syndrome: clinical manifestations in a pediatric patient

Moebius syndrome is a congenital, nonprogressive disorder clinically characterized by loss of facial expression, impaired stomatognathic system functions, incapacity to close the eyelids, and several oral impairments. The purpose of this paper was to present the clinical manifestations and the dental treatment in a 5-year, 2-month-old male Moebius syndrome patient. The child presented with facial asymmetry, difficulty performing facial mimic movements and pronouncing some letters, and compromised suction, mastication, breathing, and deglutition. An intraoral examination revealed hypofunction of the perioral muscles, cheeks and tongue, ankyloglossia, anterior open bite, and absence of carious lesions and dental anomalies. The dental treatment consisted of frenectomy and further placement of a removable orthodontic appliance with a palatal crib for correction of the anterior open bite. After 12 months of follow-up, anterior open bite decreased and speech, deglutition, and mastication improved.

[Moebius sequence: clinico-radiological findings]

INTRODUCTION

Moebius syndrome is an infrequent congenital, non-progressive disorder that is defined by facial palsy (usually bilateral) and oculomotor compromise. Its clinical spectrum is variable but it affects other cranial nerves and is associated with multiple malformations.

PATIENTS AND METHODS

We report the clinical, neurological and neuroimaging features and the progress of 20 patients (16 males and 4 females) who satisfied diagnostic criteria for Moebius sequence.

RESULTS

Ages at the first visit ranged from 9 days to 23 months. Births had been normal in 50% of the patients. Facial nerve compromise was observed in all cases, 70% being bilateral. Cranial nerves VI (85%), XII (40%), VIII (25%) and IX (60%) were also involved. Perinatal respiratory distress was seen in 35% of the patients, apnoeas in 25% and retarded development in 60% of cases. They also presented other associated malformations such as microretrognathia, ogival palate, club foot, hand and foot malformations, and four cases presented unilateral agenesis of the pectoralis major. An electromyogram study showed absence of spontaneous and voluntary activity and muscle evoked potentials on stimulating the facial nerve; magnetic resonance imaging of the brain showed hypoplasia of the trunk, agenesis of the cranial nerves and abnormalities in the posterior fossa in three of the ten cases in which the scan was performed.

CONCLUSIONS

The association of multiple malformations and dysfunction of the cranial nerves suggests a disruption in the process of morphogenesis during the embryonic period, and therefore Moebius syndrome is considered to be a malformative sequence.

Immittance measures in individuals with Moebius Sequence

Moebius Sequence has been described as a pathology which involves the VI and VII cranial nerves, causing facial palsy. Acoustic reflexes are elicited by a high intensity stimulation of the stapedius and the tensor tympani muscles. The VII cranial nerve is responsible for innervating the stapedius muscle. No acoustic reflexes are expected for individuals with this Sequence.

AIM

To describe immittance findings in a series of individuals with Moebius Sequence.

MATERIALS AND METHODS

We had 17 individuals with Moebius Sequence of both gender, with age raging from 3 to 13 years, who were submitted to otoscopy and immittance measures.

RESULTS

The results of this study indicated a Type A tympanometry in the majority of the analyzed ears, demonstrating normal function of the stapedius muscle. For the contralateral acoustic reflexes we observed it present in 50% of the ears. The ipsilateral acoustic reflexes were absent in the majority of the ears.

CONCLUSION

The results of the acoustic reflexes suggested that this measure could help in the prognosis of VII cranial nerve lesions, since half of the individual presented those reflexes.

Craniocervical junction malformation in a child with Oromandibular-limb hypogenesis-Möbius syndrome

We report a male child with Oromandibular-limb hypogenesis (OMLH), the main features being bilateral sixth and seventh nerve palsies, limb anomalies and hypoplasia of the tongue. Additional features were shortness of the neck associated with torticollis. Radiographs of the cervical spine were non-contributory, but 3D computed tomography (CT) scanning of this area identified: a) congenital hypoplasia of the atlas; b) the simultaneous development of occiput-atlas malformation/developmental defect. To our knowledge, this is the first clinical report assessing the cervico-cranium malformation in a child with OMLH-Möbius syndrome.

Moebius sequence: behaviour problems of preschool children and parental stress

This study investigates behaviour problems of preschool children with Moebius sequence, and their primary caregivers' stress. To this end, parents of all preschool children with Moebius sequence known to the German Moebius foundation were anonymously asked to fill out questionnaires, e.g. the Child Behavior Checklist [CBCL] 1.5-5. The primary caregivers of 13/22 children (seven males, six females; mean age: 3;10 [2;1-5;11] years) sent back filled-out questionnaires. Two children were rated as clinical on the CBCL-1.5-5. Boys had significantly higher scores on the scales aggressive behavior and total problems than girls. Compared to the general population, but not to other parents of mentally and / or physically handicapped children, the primary caregivers experienced higher levels of stress. In conclusion, preschool children with Moebius sequence do not show essentially increased rates of clinical behaviour problems. Nevertheless, their primary caregivers experience increased stress and need early and adequate support.

Electrophysiological assessment in patients with Möbius syndrome and clumsiness

The authors studied the nature of clumsiness in Möbius syndrome in terms of motor or sensory deficits, and sought to clarify the pathophysiological mechanism of the syndrome. Standardized electrophysiologic studies were conducted, with special emphasis on the long motor and sensory tracts and peripheral nerves, in seven Möbius patients with clumsiness, of whom six participated in MRI studies; five of them showing brainstem hypoplasia. All performed motor-evoked potentials were normal. In all patients, normal somatosensory-evoked potentials were recorded and peripheral nerve conduction assessment revealed no abnormalities. The electrophysiologic data indicate that the traversing motor and sensory tracts through the brainstem, and the peripheral nerves are not affected in Möbius syndrome.

A case of Mobius syndrome--radiological and electrophysiological findings

Mobius syndrome is characterized by congenital bilateral facial palsy and abducens nerve paralysis, but reports of radiological and electrophysiological findings are scarce. A 4-year-old boy presented with mask-like facies noted at birth after a 34-week pregnancy. Examination revealed bilateral facial and abducens nerve paralysis with no other neurological abnormalities. Computed tomography revealed bilateral absence of facial nerve canal in the middle ear. Brain magnetic resonance imaging indicated a narrow than expected nerve in the internal auditory canal (IAC). Evoked electromyography and blink reflex testing to evaluate facial nerve function yielded no responses bilaterally. Facial palsy thus appears to be caused by facial nerve dysplasia or aplasia.

[Möbius syndrome and an apparently life-threatening event]

Möbius syndrome is characterized by congenital facial weakness with impairment of ocular abduction. A subgroup of these patients have associated apneas because of involvement of brainstem respiratory centers located slightly lateral to the abducens nuclei. We report a 7-month old infant admitted to the pediatric intensive care unit because of an episode of cyanosis, hypotonia and unresponsiveness. The patient then became respirator dependent afterwards. On examination, facial diplegia, impairment of ocular abduction and hypotonia were evident. Magnetic resonance imaging (MRI) revealed abnormal signal intensity in brainstem tegmentum. At the age of 11 months he was discharged but required a home ventilator. He died 5 months later due to an infection. Möbius syndrome is associated with central respiratory dysfunction. The finding of abnormal signal intensity in brainstem tegmentum on MRI is a possible predictor of apnea in these patients.

The spectrum of Möbius syndrome: an electrophysiological study

We studied the nature and extent of facial muscle innervation and the involvement of the motor and sensory long tracts in Möbius syndrome, in order to shed light on the pathophysiological mechanism of the syndrome. Standardized blink reflexes, direct responses of the facial nerves to the orbicularis oculi muscles and concentric needle electrode electromyography in orbicularis oculi and/or oris muscles were measured in 11 patients with Möbius syndrome, of whom six participated in MRI studies, all showing absent facial nerves. We performed motor- and somatosensory-evoked potentials in seven Möbius patients. We demonstrated three distinct patterns of abnormalities suggesting different sites of the primary lesion in different patients. (i) Presence of normal blink reflexes and facial compound motor action potentials, normal habituation tests, a reduced recruitment in the facial muscles and an aberrant 'blink reflex-like' response of the orbicularis oculi muscle upon stimulation of the facial nerve region, which suggests a supranuclear origin of the defect. (ii) Absent blink reflexes, absent direct responses of the facial nerves and absent motor activity on needle electromyography, indicating a defect at the facial nuclear level. However, the nuclear defect might mask an additional supranuclear defect, which cannot, therefore, be excluded in these patients. (iii) A disperse pattern of facial compound action potentials combined with long latencies that were recorded with concentric needle electrodes, indicating involvement of motor axons in the facial nerve, possibly secondary to nuclear involvement. An additional supranuclear defect cannot be excluded in these cases. All evoked potentials studied were normal. The electrophysiological findings of the facial muscles show a spectrum of disturbances varying in degree of severity and diverse in the extent of structures involved, in 11 Möbius patients. At one end of the spectrum are patients with completely immobile faces in whom electrophysiological testing shows no signs of involvement of the facial nuclei, nerves or muscles, suggestive of a dysfunction at the supranuclear level. At the other extreme of the spectrum are patients with complete absence of responses upon facial nerve stimulation and absence of motor unit activity. This is at least indicative of a defect at the facial nuclear level. While a supranuclear defect is compatible with the concept that Möbius syndrome is a developmental disorder of the lower brainstem, intact facial nuclei as part of the syndrome has not been suggested before. The findings corroborate the concept of the Möbius syndrome being a complex regional developmental disorder of the brainstem.

Radiologic evidence for absence of the facial nerve in Möbius syndrome

OBJECTIVE

To detail the radiologic findings in Möbius syndrome, in order to clarify its pathogenetic mechanisms.

METHODS

High resolution three-dimensional T1 (MP rage) and T2 (CISS) weighted MRI were used to study the cisternal and canalicular portion of the seventh cranial nerve in six Möbius patients. Also, the anteroposterior dimension of the brainstem was measured at the level of the pons in the authors' 6 patients and in 20 age-matched healthy control subjects. Furthermore, the MRIs were evaluated for associated congenital brain anomalies.

RESULTS

The facial nerves were absent in all six patients despite residual function in some facial muscles. The authors confirmed brainstem hypoplasia but did not find tegmental calcifications. The anteroposterior dimension of the brainstem ranged between 17 and 25 mm vs 20 to 27 mm for controls. In three patients there were congenital abnormalities in the posterior fossa.

CONCLUSION

The absent facial nerves on MRI and the unusual distribution of the facial weakness, which is characteristic of Möbius syndrome, suggests that other cranial nerves, possibly the trigeminal, hypoglossal, or glossopharyngeal nerve, aberrantly innervate some lower facial muscles. Radiologic findings support the notion that Möbius syndrome is part of a more complex congenital anomaly of the fossa posterior.

Möbius sequence, Robin complex, and hypotonia: severe expression of brainstem disruption spectrum versus Carey-Fineman-Ziter syndrome

We report on nine unrelated children fitting a diagnosis of Carey-Fineman-Ziter syndrome (CFZS). All children presented with Möbius sequence, Pierre Robin complex (6/9) or micrognathia, and hypotonia. Some had primary hypoventilation, delayed development, and acral anomalies. The neuropathological investigations performed in two patients showed a combination of dysplastic lesions (neuronal heterotopias) and encephaloclastic changes consisting of small foci of necrosis with microcalcifications. The mother of a third child had severe trauma during her 2nd month of pregnancy. Based on a review of the literature on MS and CFZS, we suggest designating as "Robin-Möbius phenotype" a distinct clinical variant of MS with extensive brainstem involvement, Robin complex, hypotonia without specific muscle disorder, clubfeet and variable acral anomalies. This condition appears to bear a higher risk of mental handicap and perhaps a higher recurrence risk than "common" MS. Neuropathology and neuroimaging are suggestive, at least in some cases, of a vascular disruption, which could be exogenous, or secondary to a genetic predisposition. Etiologic heterogeneity seems likely and, in that respect, the original CFZS family could represent a private syndrome fitting on the "Robin-Möbius" spectrum. Despite the existence of two familial reports, recurrence risk is probably much lower than 25%, although exact figures cannot be extracted from the available literature.

Cognitive evaluation in adult patients with M�bius syndrome

OBJECTIVE

To establish the occurrence of mental retardation in a group of patients with Möbius syndrome and subsequently, if mental retardation is absent, to screen major aspects of memory and attention, in order to assess possible pervasive dysfunction in these cognitive domains which might be responsible for the current view that mental retardation occurs frequently in Möbius syndrome.

METHODS

In a group of 12 Dutch Möbius patients, intellectual performance, memory function and attention were assessed using a number of standardized neuropsychological tests.

RESULTS

The mean general intellectual performance did not differ significantly from that of the Dutch population. Screening of selective attention and memory did not provide indications of pervasive dysfunctions in these domains.

CONCLUSION

The rate of occurrence of mental retardation in our group of Möbius patients did not differ from that in the normal Dutch population. Furthermore, there was no evidence of attention and memory dysfunction in our group of Möbius patients.

Autism associated with conditions characterized by developmental errors in early embryogenesis: a mini review

Autism is a complex developmental disorder without an established single etiology but with significant contributions from genetic studies, functional research, and neuropsychiatric and neuroradiologic investigations. The purpose of this paper is to review the findings in five studies involving individuals manifesting the characteristic findings of autism spectrum disorder associated with malformations and dysfunctions known to result from early embryogenic defects. These investigations include two associated with teratogens (thalidomide embryopathy, Mobius sequence with misoprostol) and three (most Mobius sequence cases, CHARGE association, Goldenhar syndrome) with no known etiology. These studies suggest that early embryonic development errors often involving cranial nerve palsies, internal and external ear malformations, ophthalmologic anomalies, and a variety of systemic malformations may be associated with autism spectrum disorders statistically more frequently than expected in a normal population. Although the exact time of developmental insult for each condition cannot be identified, the evidence is that it may occur as early as week 4 to 6+ of embryogenesis.

Möbius syndrome redefined: a syndrome of rhombencephalic maldevelopment

OBJECTIVE

To investigate the variable clinical picture of Möbius syndrome (MIM no. 157900) and to further understand the pathogenesis of the disorder.

METHODS

A standardized questionnaire was submitted to 37 Dutch patients with Möbius syndrome. All underwent standardized neurologic examination with special attention to cranial nerve functions, motor skills, and facial and limb anomalies.

RESULTS

Of 37 patients with facial paresis, 97% had bilateral and 3% had unilateral ocular abduction weakness. Further analysis showed isolated abducens nerve palsy in 9%, a conjugated horizontal gaze paresis in 48%, features of Duane retraction syndrome in 34%, and congenital fibrosis of the extraocular muscles in 9%. Other signs included lingual involvement (77%), dysfunction of palate and pharynx (56%), general motor disability (88%), poor coordination (83%), and respiratory abnormalities (19%).

CONCLUSION

Möbius syndrome is more than a cranial nerve or nuclear developmental disorder. It is a syndrome of rhombencephalic maldevelopment involving predominantly motor nuclei and axons, as well as traversing long tracts. The authors also noted gaze palsies, Duane retraction syndrome, feeding and respiratory problems, and poor motor development, suggesting a regional developmental disorder.

Dynamic restoration in Möbius and Möbius-like patients

Möbius syndrome is classically characterized by bilateral facial nerve and abducens nerve paralysis in combination with limb defects. In the past 110 years, physicians diagnosed children as having the syndrome on the basis of heterogeneity of symptoms and used the term "Möbius syndrome" or "Möbius-like syndrome" for patients with multiple cranial nerve involvement. The cause and the exact pathogenesis of the syndrome still elude understanding. Genetic work-ups, radiological findings, and data from autopsies differ in their approaches and their findings of the basic causes of Möbius syndrome. In the international literature, about 301 case reports are found scattered through the past century. The appearance of the facial deformity is easy to recognize, because the Möbius patient is impaired in his or her ability to communicate nonverbally. Despite ophthalmologic problems, it is the search for a smile that brings these patients to the reconstructive surgeon. Over the past 100 years, surgical efforts attempted to improve the mask-like appearance by static and dynamic procedures, usually local muscle transpositions. Today, combinations of microsurgical procedures and aesthetic techniques are being used to restore some movement to the expressionless face of these patients by nerve and muscle transplantation. This article discusses the heterogeneity of Möbius syndrome, advocates a new classification system, presents the clinical findings of 42 patients who were seen and examined in consultation, and discusses the surgical management of 20 patients who underwent dynamic restorative microsurgery. Exemplary cases illustrating the preoperative work-up regimen and possible outcomes are reported.

Mobius sequence--a Swedish multidiscipline study

Mobius sequence/syndrome is a rare disorder characterized by congenital palsy of the 6th and 7th cranial nerves. Other cranial nerves may be affected, skeletal and orofacial anomalies and mental retardation occur. The aims were to determine the frequency of associated clinical characteristics and to identify any pregnancy or environmental factors in patients with Mobius sequence. A prospective study of 25 Swedes with apparent involvement of the 6th and 7th cranial nerves was performed and 25 patients, 1 month to 55 years old, were examined. Obvious associated systemic anomalies observed included: limb malformations (10), Poland anomaly (2), hypodontia (7), microglossia (6), cleft palate (4), hearing impairment (5) and external ear malformation (1). Pronounced functional abnormalities were observed involving facial expression (16), speech (13), eating and swallowing (12) and difficulty in sucking in infancy (11). Six patients had an autistic syndrome, one an autistic-like condition, and mental retardation was found in all these patients. No common aetiological cause was found but their mothers' pregnancy histories revealed a history of benzodiazepines (1), bleeding during pregnancy (8), spontaneous abortion (7) and chorion villus sampling in the second month of pregnancy (1). In conclusion, many patients had multiple problems with eating and communication resulting from facial palsy, cleft palate and tongue anomalies. Autism and mental retardation was diagnosed in one-third of the patients. Awareness of the wide spectrum of manifestations in Mobius sequence will assist in identification of the associated malformations and functional problems that are often seen and result in better care of the children.

Prenatal exposure to misoprostol and vascular disruption defects: a case-control study

Prenatal exposure to misoprostol has been associated with Moebius and limb defects. Vascular disruption has been proposed as the mechanism for these teratogenic effects. The present study is a multicenter, case-control study that was designed to compare the frequency of prenatal misoprostol use between mothers of Brazilian children diagnosed with vascular disruption defects and matched control mothers of children diagnosed with other types of defects. A total of 93 cases and 279 controls were recruited in eight participating centers. Prenatal exposure was identified in 32 infants diagnosed with vascular disruption defects (34.4%) compared with only 12 (4.3%) in the control group (P<0.0000001). Our data suggest that prenatal exposure to misoprostol is associated to the occurrence of vascular disruption defects in the newborns.

Segmental facial myoclonus in moebius syndrome

Moebius syndrome is characterized by sixth and seventh nerve palsy and is usually the result of bilateral hypoplasia or aplasia of the respective brain stem nuclei. There have been no reports of involuntary facial movements associated with this malformative complex. We report on a 6-year-old boy affected by Moebius syndrome with asymmetric involvement and segmental facial myoclonus with onset at age 2 years, affecting the side with partially conserved motility. Clinical presentation included congenital peripheral palsy of the right seventh cranial nerve and left-sided rhythmic rising of the upper lip and eyebrow. Surface-electromyography (EMG) of the left levator labii and frontalis muscles showed rhythmic bursting (duration: 150-450 ms; frequency: 1-3 Hz). Electroencephalographic (EEG)-polygraphic recordings and burst-locked EEG averaging failed to show any consistent EEG activity preceding the EMG bursts. Study of the blink reflex, somatosensory and motor-evoked potentials showed findings consistent with pontine pathology. Segmental facial myoclonus, although extremely rare in children, must be differentiated from several other paroxysmal motor manifestations associated with structural lesions involving the brain stem. Segmental facial myoclonus stem-Structural lesion.

Normal reading despite limited eye movements

Many investigators have demonstrated that poor readers exhibit abnormal eye movements during reading. An association between defective vergence, accommodation, and poor reading skills has also been noted by some investigators. Children who are poor readers have been subjected to therapeutic interventions on the basis of the assumption that improving their eye movements, as part of a multifaceted program of "vision therapy," will yield commensurate improvement in reading performance. This approach has been controversial, and other authors have expressed opposing views. We report the ophthalmologic and reading assessments of two children with Möbius' syndrome who were average to above-average readers despite essentially absent horizontal eye movements.