Patients with CHARGE association: a model to study saccular function in the human

Congenital deafness and vestibular disorders: a systematic literature review

Introduction

Congenital deafness is a pathological entity that represents an economical and social burden, affecting up to 0.2% of newborns in Europe. Sensorineural hearing loss (SHL) is caused by a variety of factors, including congenital abnormalities, perinatal infectious diseases and genetic syndromes. The inner ear's vestibular system, nestled alongside the auditory organs, is crucial for balance maintenance. Its close connection with the auditory system means that disturbances in one often coincide with disturbances in the other, highlighting their intertwined functions. With this review we aim to describe objective vestibular tests found in literature and to study their use for diagnosis of vestibular disturbances in patients affected by congenital deafness.

Methods

The review is conducted with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) 2020 guidelines. The search string used was: [(congenital deafness) OR (congenital hearing loss) OR (congenital hypoacusia)] AND [(vestibular disorders) OR (vertigo)]. An initial abstract reading selection was made, and a subsequent comprehensive full-text reading. For each article, we identified the type of vestibular test utilized and its corresponding outcome.

Results

Out of the initial-papers identified through the search string-articles met the eligibility criteria for further analysis through abstract and full-text reading. After further selection-articles were chosen for detailed examination, focusing on the data of patients.

Conclusion

Congenital hearing loss profoundly affects a child's development, especially in language and communication skills, and it is frequently associated with a pathological vestibular system. Early identification allows timely intervention with personalized therapies. In current literature, there is still no gold standard test to identify balance disorders in patients with congenital hearing loss. There is considerable variability on the subject due to the inclusion of diverse patients with various diagnoses, alongside a wide range of available technologies. Managing such conditions necessitates collaboration among healthcare providers, ensuring comprehensive care through prompt diagnosis and personalized treatment plans. Ongoing research aims to further improve screening methods and develop precision medicine approaches tailored to individual needs.

Implementing the chick embryo model to study vestibular developmental disorders

Children with congenital vestibular disorders show delayed motor development and challenges in maintaining posture and balance. Computed tomography images reveal that these children have abnormal inner ears in the form of a sac, with the semicircular canals missing or truncated. Little is known about how this inner ear abnormality affects central vestibular development. At present, mice with the chromodomain helicase DNA-binding protein 7 mutation are the most common model for studying congenital vestibular disorders, despite forming multiple diverse inner ear phenotypes and inducing abnormal cerebellar and visual system development. To identify the effects of a sac-like inner ear on central vestibular development, we have designed and implemented a new model, the anterior-posterior axis rotated otocyst (ARO) chick, which forms a sac-like inner ear in 85% of cases. The ARO chick is produced by anterior-posterior rotation of the otocyst at embryonic day 2. Here, we describe for the first time the 15% of ARO chicks that form three small semicircular canals and rename the ARO chicks forming sacs (ARO/s chicks). The basic features of the vestibular sensory organs in ARO/s chicks are similar to those found in patients’ sacs, and ARO/s hatchlings experience balance and walking problems like patients. Thus, ARO/s chicks have a reproducible inner ear phenotype without abnormalities in vestibular-related structures, making the model a relatively simple one to evaluate the relationship between the sac-like inner ear pathology and formation of the central vestibular neural circuitry. Here, we describe unpublished details on the surgical approaches to produce ARO chicks, including pitfalls and difficulties to avoid.

NEW & NOTEWORTHY This paper describes simple techniques for chick otocyst rotation resulting in a sac-like inner ear (85%), the common phenotype in congenital vestibular disorders. We now describe anterior-posterior axis rotated otocyst chicks, which form three small canals (15%), and rename chicks forming a sac (ARO/s chicks). Basic protocols and potential complications of otocyst rotation are described. With the use of ARO/s chicks, it will be possible to determine how the vestibular neural circuit is modified by sac-like inner ear formation.

Adaptation to Steady-State Electrical Stimulation of the Vestibular System in Humans

Objectives:

Efforts are being made toward the development of a vestibular implant. If such a device is to mimic the physiology of the vestibular system, it must first be capable of restoring a baseline or “rest” activity in the vestibular pathways and then modulating it according to the direction and velocity of head movements. The aim of this study was to assess whether a human subject could adapt to continuous electrical stimulation of the vestibular system, and whether it was possible to elicit artificial smooth oscillatory eye movements via modulation of the stimulation.

Methods:

One bilaterally deaf patient with bilateral vestibular loss received a custom-modified Med-E1 cochlear implant in which one electrode was implanted in the vicinity of the left posterior ampullary nerve. This electrode was activated with biphasic pulse trains of 400-μs phase duration delivered at a repetition rate of 200 pulses per second. The resulting eye movements were recorded with 2-dimensional binocular video-oculography.

Results:

Successive “on-off” cycles of continuous electrical stimulation resulted in a progressively shorter duration of the nystagmic response. Once the adapted state was reached upon constant stimulation, amplitude or frequency modulations of electrical stimulation produced smooth oscillatory conjugated eye movements.

Conclusions:

Although this is a case study of one patient, the results suggest that humans can adapt to electrical stimulation of the vestibular system without too much discomfort. Once the subject is in the adapted state, the electrical stimulation can be modulated to artificially elicit smooth eye movements. Therefore, the major prerequisites for the feasibility of a vestibular implant for human use are fulfilled.

Vestibulo-ocular reflex (VOR) preserved in bilateral severe vestibular malformations with internal auditory canal stenosis

A 60-year-old woman, who has suffered from bilateral deafness throughout her life, visited our outpatient clinic. Computed tomography (CT) revealed inner ear malformations, which comprise cochlear aplasia with hypoplastic vestibule in the right ear and a common cavity in the left ear, and narrow internal auditory canals. We performed electronystagmography with caloric stimulation and stimulation of earth-vertical axis rotation (EVAR) or off-vertical axis rotation (OVAR), and studied vestibular evoked myogenic potentials (VEMPs) and vestibular ocular reflex (VOR). Slight horizontal nystagmus was induced by the stimulation of EVAR but not by caloric stimulation. Slight vertical nystagmus was observed during OVAR, whereas the VEMP test elicited no response. The result of horizontal or vertical VOR performed in the dark was almost normal. These findings suggest that VOR can be acquired even with severe malformation of the inner ear whose labyrinthine functions markedly reduce bilaterally until nystagmus is slightly induced by rotation stimulation.

Quantitative analysis of limb anomalies in CHARGE syndrome: correlation with diagnosis and characteristic CHARGE anomalies

CHARGE syndrome was initially not thought to involve the limb. Several subsequent reports have shown that limb anomalies are not uncommon. To date, there have been no quantitative studies of limb anomalies in CHARGE syndrome. This study was designed to answer several questions: Do CHARGE patients with limb anomalies represent a subgroup within CHARGE syndrome? Are there correlations between certain CHARGE syndrome anomalies and limb anomalies?Are there differences between the two genders and associated limb anomalies? Are certain types of limb anomalies seen with increased frequency in CHARGE syndrome? All described patients were categorized utilizing the AI/GEN Model 2 Criteria proposed by Mitchell [1985a: J Med Syst 9:425-435]. Patients with chromosomal anomalies or familial CHARGE were excluded, as were patients with inadequate clinical descriptions, and patients in large series where individual characteristics could not be ascertained. Multivariate analysis was performed. One hundred seventy two patients with definite or probable CHARGE syndrome were analyzed. Sixty-four (37.2%) of these patients have at least one limb anomaly. Significant positive associations were seen between limb anomalies and ocular coloboma, urinary tract malformations, and genital anomalies. These associations were not significant when the definite or probable patients were analyzed separately, with the exception of genital anomalies in definite CHARGE. Gender differences were also identified. Females with tracheoesophageal fistula/esophageal atresia, or genital anomalies were more likely to have limb anomalies, while some female subgroups had positive associations between urinary tract malformations, or choanal atresia and limb anomalies. Negative associations were also seen with sensorineural hearing loss and facial paralysis. In contrast, males showed a positive association between coloboma and limb anomalies, while subgroup analysis identified positive associations with DiGeorge sequence or genital anomalies and limb anomalies. Limb anomalies are present in just over one-third of CHARGE syndrome patients. Limb anomalies are seen more frequently in association with certain CHARGE anomalies, and these associations show gender differences. There is not a common limb anomaly seen in CHARGE syndrome.

Congenital aplasia of the semicircular canals

OBJECTIVE

To describe the underrecognized inner ear malformation characterized by complete aplasia of the labyrinthine semicircular canals associated with a relatively well-formed cochlea, to investigate its relationship with known syndromic forms of hearing loss, and to hypothesize regarding the potential embryopathogenesis of this anomaly.

STUDY DESIGN

A retrospective case review consisting of cases of sensorineural hearing loss with radiographic evidence demonstrating agenesis of the semicircular canals associated with a cochlea that was either morphologically normal or sufficiently well developed to accommodate the full insertion of a cochlear implant electrode. Cases were identified by computerized tomography findings that identified the anomaly under study.

SETTING

Departments of otolaryngology and radiology in a tertiary referral center, with a large cochlear implant program serving over 800 patients, more than half of whom are children.

PATIENTS

Fifteen patients with the anomaly under study were identified.

INTERVENTIONS

Each patient underwent a complete otologic examination, audiometric studies, and high resolution computerized tomography of the temporal bone in axial and coronal planes.

MAIN OUTCOME MEASURES

The bony morphology of the cochlea, round and oval windows, vestibule, semicircular canals, and vestibular aqueduct, and the course of the facial nerve were examined. Auditory findings and otologic treatment are presented.

RESULTS

Of the 15 identified patients, 4 were nonsyndromic, 9 had CHARGE association (Coloboma of the eye, congenital Heart defects, choanal Atresia, mental and/or growth Retardation, Genital hypoplasia, and Ear anomalies and/or deafness), 1 met criteria for Noonan's syndrome, and one had features of both these syndromes. Although the cochlea was present in all cases, the cochlear morphology was usually abnormal in the CHARGE association patients. Of the 20 ears in the CHARGE subjects, only 3 ears (15%) were seen to have completely normal development of the cochlea in both the basal and upper turns. The others showed either mild hypoplasia of the upper turns (13 ears, 65%) or an incomplete partition typical of the classic Mondini deformity (4 ears, 20%). In the 4 nonsyndromic cases, one subject had bilateral Mondini dysplasia and the other three had normal cochleae. In the entire group, abnormalities of oval window development were common (20 of 30 ears, 67%), especially in the syndromic cases (18/22, 81%), but the round window was normal in the majority of cases (73%). Seven patients in the CHARGE association group had an anomalous course of the facial nerve, which was particularly severe in three. Four patients had congenital unilateral facial paralysis, although two of these children had normal radiographic anatomy of the facial nerve. One patient had bilateral facial weakness.

CONCLUSIONS

Syndromic and nonsyndromic cases of isolated semicircular canal aplasia were identified. Except for mild to moderate cochlear dysplasia, and the anomalous course of the facial nerve in some CHARGE association patients, both groups of patients were generally suitable for cochlear implantation if indicated. A high incidence of oval window aplasia with normal round window development may help to explain the embryopathogenesis of this anomaly, considering the sequence of inner ear development.

Temporal bone histopathology in CHARGE association

Three temporal bones obtained at autopsy from 2 patients with CHARGE association (Coloboma, congenital Heart disease, Atresia of choanae, mental Retardation and/or central nervous system anomalies, Genital hypoplasia, and Ear anomalies) were examined histopathologically. Both temporal bones from 1 patient showed multiple anomalies in the middle ear, inner ear, and facial nerve. However, the temporal bone obtained from the other patient showed almost normal structures in the inner ear, middle ear, and eustachian tube. These results are different from those of 2 previous reports of temporal bone histopathology regarding CHARGE association. This difference suggests that CHARGE association may arise not from one etiopathogenetic factor, but from complex factors. Special attention to dehiscent facial canal and perilymphatic gusher during otologic surgery in patients with CHARGE association is discussed.

Clinical evaluation of the hearing-impaired infant

Early identification of hearing loss and rapid rehabilitative intervention are the two key elements that will give an infant the best chance to develop normal speech and allow the family members to make appropriate adjustments that will enhance communication in the home environment. Hearing loss in an infant may be only one feature of a syndromic disorder, and the physician must aspire to diagnose and treat the entire dysfunction. While a limited laboratory evaluation and appropriate referrals to related specialties are helpful, a comprehensive history and a complete physical examination are the most effective means to identify syndromic hearing loss and to direct future evaluation and therapy.