110th ENMC International Workshop: the congenital cranial dysinnervation disorders (CCDDs). Naarden, The Netherlands, 25-27 October, 2002

Genetic investigation in a four-generation Chinese family with congenital fibrosis of extraocular muscles and keratoconus

Here, we have reported the genetic and clinical characteristics of four generations of a family patient from China with congenital fibrosis of extraocular muscles 1 (CFEOM1) and keratoconus (KC). The history of diseases, clinical observations, and blood samples of all family members were collected. A total of 100 healthy participants were recruited as normal controls. The whole exome sequencing of the genomic DNA and polymerase chain reaction were performed on samples obtained from the controls and their family members to verify the gene variants. The functional analyses of the variants were performed by using different software. Two single nucleotide polymorphisms were detected in the proband and other patients in his families, including a heterozygous missense variation, g.39726207C > T (c.2860C > T, p.R954W, rs121912585), in the third highly conserved coiled-coil domain of KIF21A, and a heterozygous missense variant, g.30664732A > C (c.136A > C, p.S46R, rs200111443) in TGFBR2. The variant p.R954W in KIF21A was predicted to be pathogenic using software, whereas p.S46R in TGFBR2 was predicted to be of uncertain significance (VUS). Thus, KC might have occurred in the proband and his daughter because of a combination of genetic mutations and involuntary eye rubbing induced by CFEOM1. This is the first case of concomitant KC in a family having CFEOM1. Thus, the study provides new information about patients with KC having CFEOM1. Furthermore, the study suggests that attention should be paid to the early detection and diagnosis of KC in patients with CFEOM1.

MRI evaluation of cranial nerve abnormalities and extraocular muscle fibrosis in duane retraction syndrome and congenital extraocular muscle fibrosis

PURPOSE

To investigate the alterations in extraocular muscles (EOMs) by magnetic resonance imaging (MRI) among patients diagnosed with Duane retraction yndrome (DRS) and congenital fibrosis of the extraocular muscles (CFEOM), who present with various cranial nerve anomalies in an attempt to enhance the clinical diagnostic process.

METHODS

A case-control study was conducted to evaluate 27 patients with DRS and 14 patients with CFEOM. All patients underwent MRI scans of the brainstem and orbital examination. Neurodevelopmental assessments were conducted through MRI, and maximum cross-sectional area and volumes of EOMs were obtained. Three types of models were constructed using machine learning decision tree algorithms based on EOMs to predict disease diagnosis, cranial nerve abnormalities, and clinical subtypes.

RESULTS

Patients with bilateral CN VI abnormalities had smaller volumes of LR, MR, and IR muscles compared to those with unilateral involvement (P < 0.05). Similarly, patients with CFEOM and unilateral third cranial nerve abnormalities had a smaller maximum cross-section of the affected eye's SR compared to the contralateral eye (P < 0.05). In patients with both CN III and CN VI abnormalities, the volume of SR was smaller than in patients with CN III abnormalities alone (P < 0.05). The prediction model using EOMs volume showed a diagnostic precision of 82.5% for clinical cases and 60.1% for predicting cranial nerve abnormalities. Nonetheless, the precision for identifying clinical subtypes was relatively modest, at only 41.7%.

CONCLUSION

The distinctive volumetric alterations in EOMs among individuals exhibiting distinct cranial nerve anomalies associated with DRS or CFEOM provide valuable diagnostic insights into to Congenital Cranial Neurodevelopmental Disorders (CCDDs). MRI analysis of EOMs should thus be regarded as a crucial diagnostic modality.

TUBB3 and KIF21A in neurodevelopment and disease

Neuronal migration and axon growth and guidance require precise control of microtubule dynamics and microtubule-based cargo transport. TUBB3 encodes the neuronal-specific β-tubulin isotype III, TUBB3, a component of neuronal microtubules expressed throughout the life of central and peripheral neurons. Human pathogenic TUBB3 missense variants result in altered TUBB3 function and cause errors either in the growth and guidance of cranial and, to a lesser extent, central axons, or in cortical neuronal migration and organization, and rarely in both. Moreover, human pathogenic missense variants in KIF21A, which encodes an anterograde kinesin motor protein that interacts directly with microtubules, alter KIF21A function and cause errors in cranial axon growth and guidance that can phenocopy TUBB3 variants. Here, we review reported TUBB3 and KIF21A variants, resulting phenotypes, and corresponding functional studies of both wildtype and mutant proteins. We summarize the evidence that, in vitro and in mouse models, loss-of-function and missense variants can alter microtubule dynamics and microtubule-kinesin interactions. Lastly, we highlight additional studies that might contribute to our understanding of the relationship between specific tubulin isotypes and specific kinesin motor proteins in health and disease.

Palpebral Fissure Changes in the Contralateral Eye in Duane Retraction Syndrome

Duane retraction syndrome (DRS) is a congenital cranial dysinnervation disorder that is characterized by paradoxical lateral rectus muscle innervation of the affected eye by axons meant to innervate the ipsilateral medial rectus muscle, with resultant varying degrees of co-contraction. It is characterized by severe abduction deficiency, variable limitation of adduction, globe retraction with narrowing of the palpebral fissure, and oblique elevation or depression on adduction. A total of 16 patients with unilateral DRS were identified. The mean age was 13 ± 8 years (range: 6 to 28 years). There were 5 males and 11 females. The cohort included 8 patients with DRS type I, 3 patients with DRS type II, 4 patients with DRS type III, and 1 patient with synergistic divergence (DRS type IV). The mean width of the palpebral fissure in primary gaze was 9.95 ± 0.25 mm, increased in abduction to 11.11 ± 1.16 mm, and changed on adduction to 10.03 ± 1.19 mm. The mean reduction in the size of the palpebral fissure on adduction was 11.7 ± 10.2% (range: 0 to 30%). The difference in the palpebral fissure width between adduction and abduction was statistically significant (P = .0018). Of the 16 patients, 8 (50%) showed narrowing of the palpebral fissure of the contralateral eye on adduction compared to abduction of more than 10%. In this case series of unilateral Duane retraction syndrome, there was a common association between widening of the palpebral fissure of the unaffected eye and adduction of the eyes with DRS in DRS types II, III, and IV and DRS type I with upshoot or downshoot. [J Pediatr Ophthalmol Strabismus. 2023;60(3):e22-e25.].

Congenital isolated unilateral third nerve palsy in children: the diagnostic contribution of high-resolution MR imaging

PURPOSE

To describe the neuroanatomical correlates of unilateral congenital isolated oculomotor palsy by means of high-resolution MRI.

METHODS

Children with a clinical diagnosis of congenital isolated oculomotr palsy and with a high-resolution MRI acquisition targeted on the orbits and cranial nerves were selected and included in the study. An experienced pediatric neuroradiologist evaluated all the exams, assessing the integrity and morphology of extraocular muscles, oculomotor, trochlear and abducens nerves as well as optic nerves and globes. Clinical data and ophthalmologic evaluations were also collected.

RESULTS

Six children (age range: 1-16 years; males: 3) were selected. All patients showed, on the affected side (left:right = 5:1), anomalies of the III nerve and extraocular muscles innervated by the pathological nerve. One patient had complete nerve agenesis, two patients showed a diffuse thinning of the nerve, from the brainstem to the orbit and 3 patients showed a distal thinning of the oculomotor nerve, starting at the level of the cavernous sinus. In all cases atrophy of corresponding muscles was noticed, but the involvement of the affected muscles varied with the nervous pattern of injury.

CONCLUSIONS

High-resolution MRI represents a valuable tool for the diagnosis of III nerve anomalies in unilateral congenital IOP, showing different patterns of nerve involvement and muscular atrophy.

Clinical and genetic characteristics of Chinese patients with congenital cranial dysinnervation disorders

BACKGROUND

Congenital cranial dysinnervation disorders (CCDDs) are a group of diseases with high clinical and genetic heterogeneity. Clinical examinations combined with Magnetic resonance imaging (MRI) and whole exome sequencing (WES) were performed to reveal the phenotypic and genotypic characteristics in a cohort of Chinese CCDDs patients.

RESULTS

A total of 122 CCDDs patients from 96 families were enrolled. All patients showed restrictive eye movements, and 46 patients from 46 families (47.9%, 46/96) were accompanied by multiple congenital malformations. Multi-positional high-resolution MRI was performed in 94 patients from 88 families, of which, all patients had hypoplasia of the cranial nerves except HGPPS patients and 15 patients from 15 families (17.0%,15/88) were accompanied by other craniocerebral malformations. WES was performed in 122 CCDDs patients. Ten pathogenic variants were detected in KIF21A, TUBB3, and CHN1 genes in 43 families. Three variants were unreported, including KIF21A (c.1064T > C, p.F355S), TUBB3 (c.232T > A, p.S78T) and CHN1 (c.650A > G, p.H217R). Of the 43 probands harboring pathogenic variants, 42 were diagnosed with Congenital Fibrosis of Extraocular Muscles (CFEOM) and one was Duane Retraction Syndrome (DRS). No definite pathogenic variants in known candidate genes of CCDDs were found in sporadic DRS, Möbius Syndrome (MBS) and Horizontal Gaze Palsy with Progressive Scoliosis (HGPPS) patients. The CFEOM patients harboring R380C, E410K and R262H variants in TUBB3 gene and F355S variant in KIF21A gene exhibited syndromic phenotypes.

CONCLUSIONS

This study broadened the phenotypic and genotypic spectrums of CCDDs, and it was the largest clinical and genetic investigation for CCDDs patients from China. KIF21A and TUBB3 were the common pathogenic genes in Chinese CFEOM. MRI coupled with WES can provide a supportive diagnosis in patients with clinically suspected CCDDs.

Optic Nerve Head and Retinal Abnormalities Associated with Congenital Fibrosis of the Extraocular Muscles

Congenital fibrosis of the extraocular muscles (CFEOM) is a congenital cranial dysinnervation disorder caused by developmental abnormalities affecting cranial nerves/nuclei innervating the extraocular muscles. Autosomal dominant CFEOM arises from heterozygous missense mutations of KIF21A or TUBB3. Although spatiotemporal expression studies have shown KIF21A and TUBB3 expression in developing retinal ganglion cells, it is unclear whether dysinnervation extends beyond the oculomotor system. We aimed to investigate whether dysinnervation extends to the visual system by performing high-resolution optical coherence tomography (OCT) scans characterizing retinal ganglion cells within the optic nerve head and retina. Sixteen patients with CFEOM were screened for mutations in KIF21A, TUBB3, and TUBB2B. Six patients had apparent optic nerve hypoplasia. OCT showed neuro-retinal rim loss. Disc diameter, rim width, rim area, and peripapillary nerve fiber layer thickness were significantly reduced in CFEOM patients compared to controls (p < 0.005). Situs inversus of retinal vessels was seen in five patients. Our study provides evidence of structural optic nerve and retinal changes in CFEOM. We show for the first time that there are widespread retinal changes beyond the retinal ganglion cells in patients with CFEOM. This study shows that the phenotype in CFEOM extends beyond the motor nerves.

Segmental Imaging of the Trochlear Nerve: Anatomic and Pathologic Considerations

BACKGROUND

The trochlear nerve (the fourth cranial nerve) is the only cranial nerve that arises from the dorsal aspect of the midbrain. The nerve has a lengthy course making it highly susceptible to injury. It is also the smallest cranial nerve and is often difficult to identify on neuroimaging.

EVIDENCE ACQUISITION

High-resolution 3-dimensional skull base MRI allows for submillimeter isotropic acquisition and is optimal for cranial nerve evaluation. In this text, the detailed anatomy of the fourth cranial nerve applicable to imaging will be reviewed.

RESULTS

Detailed anatomic knowledge of each segment of the trochlear nerve is necessary in patients with trochlear nerve palsy. A systematic approach to identification and assessment of each trochlear nerve segment is essential. Pathologic cases are provided for each segment.

CONCLUSIONS

A segmental approach to high-resolution 3-dimensional MRI for the study of the trochlear nerve is suggested.

Adding evidence to the role of NEUROG1 in congenital cranial dysinnervation disorders

Congenital cranial dysinnervation disorders (CCDDs) are a heterogeneous group of neurodevelopmental phenotypes caused by a primary disturbance of innervation due to deficient, absent, or misguided cranial nerves. Although some CCDDs genes are known, several clinical phenotypes and their aetiologies remain to be elucidated. We describe a 12-year-old boy with hypotonia, developmental delay, sensorineural hearing loss, and keratoconjunctivitis due to lack of corneal reflex. He had a long expressionless face, severe oromotor dysfunction, bilateral agenesis/severe hypoplasia of the VIII nerve with marked atresia of the internal auditory canals and cochlear labyrinth malformation. Trio-exome sequencing identified a homozygous loss of function variant in the NEUROG1 gene (NM_006161.2: c.202G > T, p.Glu68*). NEUROG1 is considered a causal candidate for CCDDs based on (i) the previous report of a patient with a homozygous gene deletion and developmental delay, deafness due to absent bilateral VIII nerves, and severe oromotor dysfunction; (ii) a second patient with a homozygous NEUROG1 missense variant and corneal opacity, absent corneal reflex and intellectual disability; and (iii) the knockout mouse model phenotype which highly resembles the disorder observed in humans. Our findings support the growing compelling evidence that loss of NEUROG1 leads to a very distinctive disorder of cranial nerves development.

Transmembrane Collagens in Neuromuscular Development and Disorders

Neuromuscular development is a multistep process and involves interactions among various extracellular and transmembrane molecules that facilitate the precise targeting of motor axons to synaptogenic regions of the target muscle. Collagenous proteins with transmembrane domains have recently emerged as molecules that play essential roles in multiple aspects of neuromuscular formation. Membrane-associated collagens with interrupted triple helices (MACITs) are classified as an unconventional subtype of the collagen superfamily and have been implicated in cell adhesion in a variety of tissues, including the neuromuscular system. Collagen XXV, the latest member of the MACITs, plays an essential role in motor axon growth within the developing muscle. In humans, loss-of-function mutations of collagen XXV result in developmental ocular motor disorders. In contrast, collagen XIII contributes to the formation and maintenance of neuromuscular junctions (NMJs), and disruption of its function leads to the congenital myasthenic syndrome. Transmembrane collagens are conserved not only in mammals but also in organisms such as C. elegans, where a single MACIT, COL-99, has been documented to function in motor innervation. Furthermore, in C. elegans, a collagen-like transmembrane protein, UNC-122, is implicated in the structural and functional integrity of the NMJ. This review article summarizes recent advances in understanding the roles of transmembrane collagens and underlying molecular mechanisms in multiple aspects of neuromuscular development and disorders.

Non-classical 1p36 deletion in a patient with Duane retraction syndrome: case report and literature review

Background

Monosomy of 1p36 is considered the most common terminal microdeletion syndrome. It is characterized by intellectual disability, growth retardation, seizures, congenital anomalies, and distinctive facial features that are absent when the deletion is proximal, beyond the 1p36.32 region. In patients with proximal deletions, little is known about the associated phenotype, since only a few cases have been reported in the literature. Ocular manifestations in patients with classical 1p36 monosomy are frequent and include strabismus, myopia, hypermetropia, and nystagmus. However, as of today only one patient with 1p36 deletion and Duane retraction syndrome (DRS) has been reported.

Case presentation

We describe a patient with intellectual disability, facial dysmorphism, and bilateral Duane retraction syndrome (DRS) type 1. Array CGH showed a 7.2 Mb de novo deletion from 1p36.31 to 1p36.21.

Discussion

Our patient displayed DRS, which is not part of the classical phenotype and is not a common clinical feature in 1p36 deletion syndrome; we hypothesized that this could be associated with the overlapping deletion between the distal and proximal 1p36 regions. DRS is one of the Congenital Cranial Dysinnervation Disorders, and a genetic basis for the syndrome has been extensively reported. The HES3 gene is located at 1p36.31 and could be associated with oculomotor alterations, including DRS, since this gene is involved in the development of the 3rd cranial nerve and the 6th cranial nerve’s nucleus. We propose that oculomotor anomalies, including DRS, could be related to proximal 1p36 deletion, warranting a detailed ophthalmologic evaluation of these patients.

Superior Rectus Transposition With Medial Rectus Recession Versus Medial Rectus Recession in Esotropic Duane Retraction Syndrome

PURPOSE

To compare the results of augmented superior rectus transposition (with or without medial rectus recession) with simple medial rectus recession in the treatment of patients with esotropic Duane retraction syndrome.

METHODS

This was a prospective, randomized, and interventional comparative study of 20 patients with esotropic type 1 Duane retraction syndrome. Patients were randomly divided into two groups. In the first group (superior rectus transposition group), superior rectus transposition with or without medial rectus recession was performed. In the second group (non-superior rectus transposition group), unilateral medial rectus recession was performed.

RESULTS

Each group included 10 patients. Esotropia improved from 20.4 prism diopters (PD) preoperatively to 0.6 PD postoperatively in the superior rectus transposition group and from 22.5 PD preoperatively to 0.9 PD postoperatively in the non-superior rectus transposition group. Face turn improved from 11.5° preoperatively to 0.5° postoperatively in the superior rectus transposition group and from 12° preoperatively to 1.5° postoperatively in the non-superior rectus transposition group. Abduction improved in the superior rectus transposition group from -3.9 preoperatively to -3.1 postoperatively and from -3.9 preoperatively to -3.6 postoperatively in the non-superior rectus transposition group. Vertical deviation developed in two cases in the superior rectus transposition group.

CONCLUSIONS

Both superior rectus transposition and medial rectus recession are effective in the elimination of esotropia and face turn in patients with esotropic Duane retraction syndrome. Superior rectus transposition is more effective in improving abduction, but it can be complicated by vertical deviation. [J Pediatr Ophthalmol Strabismus. 2020;57(5):309-318.].

TUBB3 E410K syndrome: Case report and review of the clinical spectrum of TUBB3 mutations

The tubulinopathies refer to a wide range of brain malformations caused by mutations in one of the seven genes encoding different tubulin's isotypes. The β-tubulin isotype III (TUBB3) gene has a primary function in nervous system development and axon generation and maintenance, due to its neuron-specific expression pattern. A recurrent heterozygous mutation, c.1228G > A; p.E410K, in TUBB3 gene is responsible of a rare disorder clinically characterized by congenital fibrosis of the extraocular muscle type 3 (CFEOM3), intellectual disability and a wide range of neurological and endocrine abnormalities. Other mutations have been described spanning the entire gene and genotype-phenotype correlations have been proposed. We report on a 3-year-old boy in whom clinical exome sequencing allowed to identify a de novo TUBB3 E410K mutation as the molecular cause underlying a complex phenotype characterized by a severe bilateral palpebral ptosis refractory to eye surgery, psychomotor delay, absent speech, hypogonadism, celiac disease, and cyclic vomiting. Brain MRI revealed thinning of the corpus callosum with no evidence of malformation cortical dysplasia. We reviewed available records of patients with TUBB3 E410K mutation and compared their phenotype with the clinical outcome of patients with other mutations in TUBB3 gene. The present study confirms that TUBB3 E410K results in a clinically recognizable phenotype, unassociated to the distinct cortical dysplasia caused by other mutations in the same gene. Early molecular characterization of TUBB3 E410K syndrome is critical for targeted genetic counseling and prompt prospective care in term of neurological, ophthalmological, endocrine, and gastrointestinal follow-up.

The clinical characteristics of Duane retraction syndrome in Al-Medina region

Purpose

To assess the clinical characteristics of Duane Retraction Syndrome (DRS) in Al-Medina region, in patients attending a pediatric ophthalmology clinic at Ohud Hospital.

Method

A cross-sectional observational study was conducted from October 2017 to June 2018 at Ohud Hospital, Al-Medina region, Saudi Arabia. Data was collected using a sheet containing eighteen simple items which include demographic data, family history, surgical history, the clinical characteristics of the disease and the physician's treatment plan. Twenty patients were included in this study.

Results

All twenty patients included in the study were diagnosed with DRS type I. Male and female were symmetrical in numbers as both 10 (50.0%) respectively. The mean age of the subjects was 8.7 years (SD 9.6). 95% of the subject were unilaterally affected while five percent of them were affected both sides of the eyes. 75% of the patients were affected on the left eye while 20% were affected on the right side. 35% of the patients had amblyopia in the affected eye. 25% of the patients had an abnormal head position. Abnormal eye movement (upshoot and downshoot) more common when the right eye is affected (p-0.035). 75% of the patients were orthotropic while 30% had esotropia. 75% of patients were positive of parents' consanguinity. 16 patients (80.0%) were from Al-Medina city while four of them (20.0%) were from the different area of Al-Medina region (Al Hejeria, Al Henakia, Omluj, Yatmah).

Conclusion

This cross-sectional observational study is the first one that evaluates DRS in Al-Medina region. Associated abnormal eye movement more common when the right eye is affected. Parents' consanguinity may play a role in the occurrence of DRS as it is not considered as a rare disease in our region. Therefore, more studies are needed to establish the relationship between the occurrence of DRS and parents' consanguinity in our region. Also, further studies are needed to establish the relationship between abnormal eye movement and the involvement of the right eye.

Clinical and Genetic Heterogeneity in Six Tunisian Families With Horizontal Gaze Palsy With Progressive Scoliosis: A Retrospective Study of 13 Cases

Background: Horizontal Gaze Palsy with Progressive Scoliosis (HGPPS) is a rare autosomal recessive congenital disorder characterized by the absence of conjugate horizontal eye movements, and progressive debilitating scoliosis during childhood and adolescence. HGPPS is associated with mutations of the ROBO3 gene. In this study, the objective is to identify pathogenic variants in a cohort of Tunisian patients with HGPPS and to further define ROBO3 genotype-phenotype correlations. Methods: Thirteen Tunisian patients from six unrelated consanguineous families all manifesting HGPPS were genetically investigated. We searched for the causative variants for HGPPS using classical Sanger and whole exome sequencing. Results: Four distinct homozygous mutations were identified in ROBO3 gene. Two of these were newly identified homozygous and non-synonymous mutations, causing effectively damage to the protein by in silico analysis. The other two mutations were previously reported in Tunisian patients with HGPPS. Mutations were validated by Sanger sequencing in parents and affected individuals. Conclusion: To the best of our knowledge, this is the largest ever reported cohort on families with HGPPS in whom ROBO3 mutations were identified. These molecular findings have expanded our knowledge of the ROBO3 mutational spectrum. The relevance of our current study is two-fold; first to assist proper management of the scoliosis and second to protect families at risk.

Congenital fibrosis of the extra-ocular muscles (CFEOM) and the cranial dysinnervation disorders

Congenital fibrosis of the extraocular muscles (CFEOM) is one of the congenital cranial dysinnervation disorders (CCDDs). This review discusses the characteristics of the CFEOM phenotypes and the CCDDs, the fibrosis associated with these disorders and the processes, and genes involved in the embryological development of cranial neuromuscular units. In particular, it focuses on the genetics of neural crest identity, axon guidance, and axon construction in relation to the CFEOMs and some consideration of treatment strategies.

Magnetic Resonance Imaging in 14 Patients with Congenital Oculomotor Nerve Palsy

PURPOSE

To elucidate the imaging findings of congenital oculomotor nerve palsy by evaluating the oculomotor nerve and extraocular muscles on magnetic resonance (MR) imaging in a relatively large series of 14 patients with congenital oculomotor nerve palsy.

METHODS

Ophthalmologic examination of 14 consecutive patients diagnosed with congenital oculomotor nerve palsy, and MR imaging of the orbit and oculomotor nerves were performed.

RESULTS

Of the 14 patients with congenital oculomotor nerve palsy, 13 patients (93%) were unilateral and 12 patients (86%) had incomplete palsy. On MR imaging, 5 patients (36%) had hypoplasia or aplasia of the oculomotor nerve with variable degrees of extraocular muscle atrophy on the affected side. Of the 14 patients, nine (64%) had normal-sized oculomotor nerves with or without muscle atrophy. The most frequently involved muscles were the inferior rectus (64%) and medial rectus (50%), followed by the superior rectus (29%) and inferior oblique muscles (14%). None of the 14 patients showed an abnormal abducens nerve.

CONCLUSION

Congenital oculomotor nerve palsy was mostly incomplete and hypoplasia or aplasia of the oculomotor nerve was apparent in one third of patients showing variable degrees of extraocular muscle atrophy, mostly of the medial rectus and inferior rectus muscles.

Ophthalmoplegia and Congenital Cranial Dysinnervation Disorders

Some forms of ophthalmoplegia are congenital and fall into the category of Congenital Cranial Dysinnervation Disorders (CCDDs). These disorders arise from a primary defect of cranial nucleus/nerve development or guidance. Many have substantial limitations of ocular motility with or without other associated features. The type and degree of ophthalmoplegia can be similar between CCDD subtypes as well as with non-congenital forms of ophthalmoplegia. Therefore diagnostic confirmation often requires neuro-imaging and/or genetic investigations. The clinician should consider this category in cases of ophthalmoplegia that are congenital and nonprogressive in nature.

Ocular congenital cranial dysinnervation disorders (CCDDs): insights into axon growth and guidance

Unraveling the genetics of the paralytic strabismus syndromes known as congenital cranial dysinnervation disorders (CCDDs) is both informing physicians and their patients and broadening our understanding of development of the ocular motor system. Genetic mutations underlying ocular CCDDs alter either motor neuron specification or motor nerve development, and highlight the importance of modulations of cell signaling, cytoskeletal transport, and microtubule dynamics for axon growth and guidance. Here we review recent advances in our understanding of two CCDDs, congenital fibrosis of the extraocular muscles (CFEOM) and Duane retraction syndrome (DRS), and discuss what they have taught us about mechanisms of axon guidance and selective vulnerability. CFEOM presents with congenital ptosis and restricted eye movements, and can be caused by heterozygous missense mutations in the kinesin motor protein KIF21A or in the β-tubulin isotypes TUBB3 or TUBB2B. CFEOM-causing mutations in these genes alter protein function and result in axon growth and guidance defects. DRS presents with inability to abduct one or both eyes. It can be caused by decreased function of several transcription factors critical for abducens motor neuron identity, including MAFB, or by heterozygous missense mutations in CHN1, which encodes α2-chimaerin, a Rac-GAP GTPase that affects cytoskeletal dynamics. Examination of the orbital innervation in mice lacking Mafb has established that the stereotypical misinnervation of the lateral rectus by fibers of the oculomotor nerve in DRS is secondary to absence of the abducens nerve. Studies of a CHN1 mouse model have begun to elucidate mechanisms of selective vulnerability in the nervous system.

What's new for us in strabismus?

Strabismus is one of the most challenging subspecialties encountered in the field of ophthalmology. The concept of etiology of strabismus is being advanced with the development of newer imaging modalities and increased understanding of the genetics of strabismus. Imaging is also being used to aid in the planning of strabismus surgery. Newer horizons are being explored in the amblyopia management. The good old eye-pad is being replaced with the iPad. Early detection of loss of stereopsis is being used to decide the timing for strabismus surgery. Improvement of binocular summation has been discovered as a benefit of corrective strabismus surgery. Newer surgical techniques such as new transposition procedures are being developed to correct complex strabismus. Strabismus surgeries aided by adjustable sutures have increased the precision of a strabismologist. A new light has been thrown on the psychosocial impact of strabismus. A present-day strabismologist has advanced from the goal of ocular alignment to a bigger perspective "to regain the paradise lost: stereopsis."

Clinical correlation of imaging findings in congenital cranial dysinnervation disorders involving abducens nerve

PURPOSE

High-resolution magnetic resonance imaging (MRI) of intracranial parts of sixth nerve and seventh nerve and the extraocular muscles (EOMs) in orbit to correlate the clinical characteristics in patients with two special forms of strabismus in congenital cranial dysinnervation disorders which are Duane's retraction syndrome (DRS) and Mobius syndrome.

MATERIALS AND METHODS

Morphological analysis by 3T MRI of orbit (using surface coils) and brain (using 32 channel head coil) was performed on 6 patients with clinical DRS (1 bilateral), 2 cases with Mobius syndrome, and 1 case with congenital sixth nerve palsy. These were compared with findings in five controls.

RESULTS

We observed absence/hypoplasia of sixth nerve in five out of seven eyes with DRS (71.42%), anomalous course in one eye, sixth and seventh nerve absence/hypoplasia in affected eyes with Mobius syndrome and bilateral absence/hypoplasia of the sixth nerve in congenital sixth nerve palsy. For EOMs we calculated maximum diameter, area, and circumference of muscles using Osirix software, and noticed significant hypoplasia of lateral rectus in comparison to controls (P < 0.001).

CONCLUSIONS

MRI gives useful information regarding confirmation of clinical diagnosis and its neurological anomalies in complex cases and helps to plan tailor made surgical management.

Eyelid Retraction in Isolated Unilateral Congenital Blepharoptosis

Isolated unilateral congenital ptosis is encountered relatively infrequently in clinical practice. It typically consists of a unilateral droopy eyelid, weak levator palpebrae superioris muscle function, lid lag, and an absent upper lid crease with no other abnormalities on examination. We present a four-and-a-half-year-old girl with isolated and mild unilateral congenital ptosis who unexpectedly demonstrated a static upper eyelid on downgaze in conjunction with a well-formed upper lid skin crease. We attribute this uncommon sign in congenital ptosis to stiffness and presumed fibrosis of the levator muscle. Examining the function of the eyelids in all directions of gaze is important in patients with abnormalities of lid position, since additional useful information can be gleaned about the status of the levator muscle including, aberrant regeneration or fibrosis.

Imaging of Cranial Nerves III, IV, VI in Congenital Cranial Dysinnervation Disorders

Congenital cranial dysinnervation disorders are a group of diseases caused by abnormal development of cranial nerve nuclei or their axonal connections, resulting in aberrant innervation of the ocular and facial musculature. Its diagnosis could be facilitated by the development of high resolution thin-section magnetic resonance imaging. The purpose of this review is to describe the method to visualize cranial nerves III, IV, and VI and to present the imaging findings of congenital cranial dysinnervation disorders including congenital oculomotor nerve palsy, congenital trochlear nerve palsy, Duane retraction syndrome, Möbius syndrome, congenital fibrosis of the extraocular muscles, synergistic divergence, and synergistic convergence.

Clinical presentation and management of congenital ptosis

Congenital ptosis is a rare condition characterized by lower positioning of the upper eyelid that is present at birth and is a clinical condition that is persistent if not treated. It may be unilateral or bilateral and may be associated with other ocular disorders or systemic conditions, including Marcus Gunn, Horner, and Duane syndromes. It is a benign condition but causes functional, cosmetic, and psychological problems in children. However, not all patients need to undergo surgery, and usually only patients at risk of amblyopia need a prompt surgical correction, while in other cases, surgery can be postponed. The grade of ptosis, the eyelid function, and the amblyopic risk are the parameters that affect the ophthalmologist’s decision on timing of surgery and the surgical technique to be used. In fact, there are several types of surgical techniques to correct a congenital ptosis, although very often more than one is needed to obtain an acceptable result. This paper reviews the causes of congenital ptosis and associated diseases. Particular emphasis is given to surgical management and different procedures available to correct the upper eyelid anomaly and avoid permanent damage to visual function.

Congenital cranial dysinnervation disorders

The European Neuromuscular Centre (ENMC) derived the term Congenital Cranial Dysinnervation Disorders in 2002 at an international workshop for a group of congenital neuromuscular diseases. CCDDs are congenital, non-progressive ophthalmoplegia with restriction of globe movement in one or more fields of gaze. This group of sporadic and familial strabismus syndromes was initially referred to as the 'congenital fibrosis syndromes' because it was assumed that the primary pathologic process starts in the muscles of eye motility. Over the last few decades, evidence has accumulated to support that the primary pathologic process of these disorders is neuropathic rather than myopathic. This is believed that for normal development of extra ocular muscles and for preservation of muscle fiber anatomy, normal intra-uterine development of the innervation to these muscles is essential. Congenital dysinnervation to these EOMs can lead to abnormal muscle structure depending upon the stage and the extent of such innervational defects. Over last few years new genes responsible for CCDD have been identified, permitting a better understanding of associated phenotypes, which can further lead to better classification of these disorders. Introduction of high-resolution MRI has led to detailed study of cranial nerves courses and muscles supplied by them. Thus, due to better understanding of pathophysiology and genetics of CCDDs, various treatment modalities can be developed to ensure good ocular alignment and better quality of life for patients suffering from the same.

Abducens Nerve in Patients with Type 3 Duane's Retraction Syndrome

Background

We have previously reported that the presence of the abducens nerve was variable in patients with type 3 Duane’s retraction syndrome (DRS), being present in 2 of 5 eyes (40%) and absent in 3 (60%) on magnetic resonance imaging (MRI). The previous study included only 5 eyes with unilateral DRS type 3.

Objectives

To supplement existing scarce pathologic information by evaluating the presence of the abducens nerve using high resolution thin-section MRI system in a larger number of patients with DRS type 3, thus to provide further insight into the pathogenesis of DRS.

Data Extraction

A retrospective review of medical records on ophthalmologic examination and high resolution thin-section MRI at the brainstem level and orbit was performed. A total of 31 patients who showed the typical signs of DRS type 3, including abduction and adduction deficit, globe retraction, narrowing of fissure on adduction and upshoot and/or downshoot, were included. The abducens nerve and any other extraocular muscle abnormalities discovered by MRI were noted.

Results

DRS was unilateral in 26 patients (84%) and bilateral in 5 patients (16%). Two out of 5 bilateral patients had DRS type 3 in the right eye and DRS type 1 in the left eye. Of the 34 affected orbits with DRS type 3 in 31 patients, the abducens nerve was absent or hypoplastic in 31 eyes (91%) and present in 3 eyes (9%). Patients with a present abducens nerve showed more limitation in adduction compared to patients with an absent abducens nerve (P = 0.030).

Conclusions

The abducens nerve is absent or hypoplastic in 91% of DRS type 3. Patients with a present abducens nerve showed more prominent limitation of adduction. As DRS type 3 partly share the same pathophysiology with type 1 and 2 DRS, the classification of DRS may have to be revised according to MRI findings.

A rare case of congenital fibrosis of extraocular muscle type 1A due to KIF21A mutation with Marcus Gunn jaw-winking phenomenon

BACKGROUND

Congenital fibrosis of the extraocular muscles (CFEOM1) is classically a congenital, non-progressive, restrictive strabismus syndrome characterized by bilateral ptosis and ophthalmoplegia with an infraducted position of the globes. This autosomal dominant syndrome is caused by mutations in the KIF21A gene.

METHODS AND RESULTS

In this report we describe a 5-year-old boy, and his mother, both of whom have a mutation in the KIF21A gene, who possesses typical features of CFEOM1 syndrome. Besides displaying typical features of CFEOM1, he demonstrated Marcus Gunn jaw-winking phenomenon. The patient additionally had a positive family history of such features.

CONCLUSION

This is first report of the coexistence of CFEOM and Marcus Gunn jaw-winking phenomenon in a patient with a KIF21A mutation from Turkey. We explain the phenotypic findings associated with mutations in KIF21A including CFEOM1A and Marcus Gunn jaw-winking phenomenon.

Considerations on the etiology of congenital Brown syndrome

PURPOSE OF REVIEW

Brown syndrome is an ocular motility disorder characterized by limited volitional and passive elevation of the eye in adduction. Although originally thought due to abnormalities in the trochlea or tendon sheath (limiting the free movement of the tendon through the trochlea), recent evidence suggests that some cases of congenital Brown syndrome may be related to neurodevelopmental abnormalities of the extraocular muscles (congenital cranial dysinnervation disorders, CCDD).

RECENT FINDINGS

CCDD is a term encompassing congenital abnormalities of eye movements caused by congenital innervational abnormalities. The abnormal development of cranial nerve nuclei or abnormalities in cranial nerve axonal transport affects the development of the extraocular muscle(s). Currently, congenital fibrosis of the extraocular muscles, Duane syndrome, Moebius syndrome, Horizontal gaze palsy and progressive scoliosis, and synergistic divergence are included as CCDDs. In addition, congenial ptosis, Jaw Wink ptosis, and congenital superior oblique palsy are also included. Recently, it has been suggested that some cases of congenital Brown syndrome and congenital superior oblique paresis are related, and these entities may be part of the CCDDs spectrum.

SUMMARY

Important findings regarding the cause of congenital Brown syndrome will be reviewed.

The congenital cranial dysinnervation disorders

Congenital cranial dysinnervation disorders (CCDD) encompass a number of related conditions and includes Duane syndrome, congenital fibrosis of the external ocular muscles, Möbius syndrome, congenital ptosis and hereditary congenital facial paresis. These are congenital disorders where the primary findings are non-progressive and are caused by developmental abnormalities of cranial nerves/nuclei with primary or secondary dysinnervation. Several CCDD genes have been found, which enhance our understanding of the mechanisms involved in brain stem development and axonal guidance.

Magnetic resonance imaging in congenital Brown syndrome

AIMS

Our aim was to elucidate the etiology of Brown syndrome by evaluating the trochlea position, morphologic characteristics of the extraocular muscles including superior oblique muscle/tendon complex, and the presence of the cranial nerves (CN) III, IV, and VI using magnetic resonance imaging (MRI) in eight patients with unilateral congenital Brown syndrome and one patient with bilateral congenital Brown syndrome.

METHODS

Nine consecutive patients diagnosed with congenital Brown syndrome had a comprehensive ocular examination and MRI for the CN III, CN VI, and the extraocular muscles. Five of the nine patients underwent additional high resolution MRI for CN IV. The distance from the annulus of Zinn to the trochlea was measured.

RESULTS

Normal sized CN III, IV, and VI, as well as all extraocular muscles, could be identified bilaterally in all patients with available MRI. The distance from the annulus of Zinn to the trochlea was the same in both eyes.

CONCLUSIONS

The findings for our patients, particularly in those who underwent additional high resolution MRI, did not provide evidence of a lack of CN IV as a cause of Brown syndrome.

Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder

Abnormal ocular motility is a common clinical feature in congenital cranial dysinnervation disorder (CCDD). To date, eight genes related to neuronal development have been associated with different CCDD phenotypes. By using linkage analysis, candidate gene screening, and exome sequencing, we identified three mutations in collagen, type XXV, alpha 1 (COL25A1) in individuals with autosomal-recessive inheritance of CCDD ophthalmic phenotypes. These mutations affected either stability or levels of the protein. We further detected altered levels of sAPP (neuronal protein involved in axon guidance and synaptogenesis) and TUBB3 (encoded by TUBB3, which is mutated in CFEOM3) as a result of null mutations in COL25A1. Our data suggest that lack of COL25A1 might interfere with molecular pathways involved in oculomotor neuron development, leading to CCDD phenotypes.

Congenital and Genetic Ocular Motility Disorders: Update and Considerations

Concepts regarding certain forms of congenital eye movement disorders have recently changed, due in large part to new genetic evidence identifying causative genes and their role in the development of extraocular muscle innervation. This group is now referred to as the Congenital Cranial Dysinnervation Disorders (CCDDs). Careful assessment of phenotypic features that include both ophthalmological and non-ophthalmological features in genetically defined individuals has led to the development of a more robust classification system. Correlating phenotypes with new genetically defined syndromes has improved the ability of the clinician/researcher to better determine a definitive diagnosis in patients with complex ocular motility disorders. Nevertheless, more work is still required.

The ECEL1-related strabismus phenotype is consistent with congenital cranial dysinnervation disorder

BACKGROUND

Congenital cranial dysinnervation disorders (CCDDs) are phenotypes of congenital incomitant strabismus and/or ptosis related to orbital dysinnervation. CCDDs have been associated with dominant or recessive monogenic mutations in at least 7 different genes (CHN1, SALL4, HOXA1, KIF21A, PHOX2A, TUBB3, ROBO3) that cause phenotypes such as Duane retraction syndrome, congenital fibrosis of the extraocular muscles, and horizontal gaze palsy with progressive scoliosis. Recently, arthrogryposis with or without strabismus has been shown to be caused by recessive mutations in ECEL1, a gene likely involved in neuromuscular junction formation. The strabismus phenotype in ECEL1-related cases has not always been detailed but may be a form of CCDD. To better define the ECEL1-related ophthalmic phenotype, we detail ophthalmic findings in 4 affected siblings from a consanguineous family and review documented ophthalmic findings for other reported mutation-positive cases.

METHODS

Affected family members were prospectively examined and the relevant literature was reviewed.

RESULTS

Ophthalmic findings were present in 3 of the 4 siblings with ECEL1-related distal arthrogryposis: bilateral ptosis with bilateral congenital fibrosis of the extraocular muscles, right ptosis with ipsilateral Y exotropia (exotropia increasing in upgaze), and right ptosis with ipsilateral Duane retraction syndrome. The fourth affected sibling, who had the mildest arthrogryposis, had no ophthalmic abnormalities. Of 26 other reported recessive ECEL1 mutation cases (14 families), all had arthrogryposis, 19 had documented ptosis, and 4 had documented complex strabismus. One of these cases had both documented ptosis and complex strabismus.

CONCLUSIONS

Our clinical findings are consistent with recessive ECEL1 mutations causing variably penetrant orbital dysinnervation phenotypes (ptosis and/or complex strabismus with abnormal synkinesis) in the context of arthrogryposisis, that is, with the ECEL1-related ophthalmic phenotype being a form of CCDD.

Limited ocular motility in a child with 3q23 microdeletion ("blepharophimosis syndrome plus")

Blepharophimosis syndrome is a recognizable ocular phenotype (blepharophimosis, telecanthus, ptosis, and epicanthus inversus) caused by heterozygous (dominant) intragenic mutation in FOXL2 (chromosome 3q23), which can also cause premature ovarian failure. A deletion that involves not only FOXL2 but also adjacent genes can result in additional clinical features ("blepharophimosis syndrome plus"). Studies of such patients are useful because observed additional clinical features suggest potential functions of genes adjacent to FOXL2. The authors describe a boy with blepharophimosis syndrome plus from a de novo heterozygous 3q22.3-q24 11.2 Mb microdeletion. Among his additional clinical features was bilateral limitation of abduction and supraduction, which suggests that the deleted area includes a gene responsible for ocular motility.

Retinal Dysfunction in Patients with Congenital Fibrosis of the Extraocular Muscles Type 2

INTRODUCTION

Congenital fibrosis of the extraocular muscles type 2 (CFEOM2) is a distinct non-syndromic form of congenital incomitant strabismus secondary to orbital dysinnervation from recessive mutations in the gene PHOX2A. The phenotype includes bilateral ptosis, very large angle exotropia, ophthalmoplegia, and poorly-reactive pupils. Other than amblyopia, afferent visual dysfunction has not been considered part of CFEOM2; however, we have repeatedly observed non-amblyopic subnormal vision in affected patients. The purpose of this study was to document this recurrent feature of the phenotype.

METHODS

A retrospective case series (2002-2012).

RESULTS

Eighteen patients (four families) were identified; all affected individuals had confirmed homozygous recessive PHOX2A mutations except one individual for whom genetic testing was not done because of multiple genetically confirmed family members. Age at assessment ranged from 5-62 years old (median 10 years old). All patients had decreased best-corrected visual acuity not completely explainable by amblyopia in both the preferred and non-preferred eye. In those patients who had further ancillary testing, visual fields (five patients) and electroretinography (10 patients) confirmed abnormalities not ascribable to amblyopia.

CONCLUSIONS

In addition to a distinct form of congenital incomitant strabismus, the phenotype of CFEOM2 includes subnormal vision consistent with retinal dysfunction. This could be the direct result of PHOX2A mutations or a secondary effect of orbital dysinnervation.

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.

Fourth cranial nerve palsy and Brown syndrome: two interrelated congenital cranial dysinnervation disorders?

Based on neuroimaging data showing absence of the trochlear nerve, congenital superior oblique palsy is now classified as a congenital cranial dysinnervation disorder. A similar absence of the abducens nerve is accompanied by misinnervation to the lateral rectus muscle from a branch of oculomotor nerve in the Duane retraction syndrome. This similarity raises the question of whether some cases of Brown syndrome could arise from a similar synkinesis between the inferior and superior oblique muscles in the setting of congenital superior oblique palsy. This hypothesis has gained support from the confluence of evidence from a number of independent studies. Using Duane syndrome as a model, we critically review the accumulating evidence that some cases of Brown syndrome are ultimately attributable to dysgenesis of the trochlear nerve.

Expanding the phenotypic spectrum of ECEL1-related congenital contracture syndromes

Using a combination of homozygosity mapping and whole-exome sequencing (WES), we identified a novel missense c.1819G>A mutation (G607S) in the endothelin-converting enzyme-like 1 (ECEL1) gene in a consanguineous pedigree of Turkish origin presenting with a syndrome of camptodactyly, scoliosis, limited knee flexion, significant refractive errors and ophthalmoplegia. ECEL1 mutations were recently reported to cause recessive forms of distal arthrogryposis. This report expands on the molecular basis and the phenotypic spectrum of ECEL1-associated congenital contracture syndromes.

Inherited KIF21A and PAX6 gene mutations in a boy with congenital fibrosis of extraocular muscles and aniridia

Background

Mutations in the KIF21A gene are detected in the patients with congenital fibrosis of the extraocular muscles. Mutations in the PAX6 gene are detected in the patients with congenital aniridia.

Case presentation

Herein we report a boy with both congenital fibrosis of extraocular muscles and aniridia. Sequence analysis of his KIF21A and PAX6 genes reveals a 1-bp deletion (c.745delC) in the PAX6 gene and a missense mutation of c.2860C > T (p.Arg954Trp) in KIF21A.

Conclusions

This study demonstrates that the occurrence of independent mutations in more than a single gene in a patient may lead to a complex phenotype.

Midbrain and hindbrain malformations: advances in clinical diagnosis, imaging, and genetics

Historically, the midbrain and hindbrain have been considered of secondary importance to the cerebrum, which has typically been acknowledged as the most important part of the brain. In the past, radiologists and pathologists did not regularly examine these structures-also known as the brainstem and cerebellum-because they are small and difficult to remove without damage. With recent developments in neuroimaging, neuropathology, and neurogenetics, many developmental disorders of the midbrain and hindbrain have emerged as causes of neurodevelopmental dysfunction. These research advances may change the way in which we treat these patients in the future and will enhance the clinical acumen of the practising neurologist and thereby improve the diagnosis and treatment of these patients.

A boy with homozygous microdeletion of NEUROG1 presents with a congenital cranial dysinnervation disorder [Moebius syndrome variant]

Background

We report on a 6-year-old Turkish boy with profound sensorineural deafness, balance disorder, severe disorder of oral motor function, and mild developmental delay. Further findings included scaphocephaly, plagiocephaly, long palpebral fissures, high narrow palate, low-set posteriorly rotated ears, torticollis, hypoplastic genitalia and faulty foot posture. Parents were consanguineous.

Methods and results

Computed tomography and magnetic resonance imaging showed bilateral single widened cochlear turn, narrowing of the internal auditory canal, and bilateral truncation of the vestibulo-cochlear nerve. Microarray analysis and next generation sequencing showed a homozygous deletion of chromosome 5q31.1 spanning 115.3 kb and including three genes: NEUROG1 (encoding neurogenin 1), DCNP1 (dendritic cell nuclear protein 1, C5ORF20) and TIFAB (TIFA-related protein). The inability to chew and swallow, deafness and balance disorder represented congenital palsies of cranial nerves V (trigeminal nerve) and VIII (vestibulo-cochlear nerve) and thus a congenital cranial dysinnervation disorder.

Conclusions

Based on reported phenotypes of neurog1 null mutant mice and other vertebrates, we strongly propose NEUROG1 as the causative gene in this boy. The human NEUROG1 resides within the DFNB60 locus for non-syndromic autosomal recessive deafness on chromosome 5q22-q31, but linkage data have excluded it from being causative in the DFNB60 patients. Given its large size (35 Mb, >100 genes), the 5q22-q31 area could harbor more than one deafness gene. We propose NEUROG1 as a new gene for syndromic autosomal recessive hearing loss and congenital cranial dysinnervation disorder including cranial nerves V and VIII.