Mondini dysplasia and congenital cytomegalovirus infection

Hearing loss associated with enlargement of the vestibular aqueduct: mechanistic insights from clinical phenotypes, genotypes, and mouse models

Enlargement of the vestibular aqueduct (EVA) is one of the most common inner ear malformations associated with sensorineural hearing loss in children. The delayed onset and progressive nature of this phenotype offer a window of opportunity to prevent or retard progression of hearing loss. EVA is not the direct cause of hearing loss in these patients, but rather is a radiologic marker for some underlying pathogenetic defect. Mutations of the SLC26A4 gene are a common cause of EVA. Studies of an Slc26a4 knockout mouse demonstrate that acidification and enlargement of the scala media are early events in the pathogenesis of deafness. The enlargement is driven by fluid secretion in the vestibular labyrinth and a failure of fluid absorption in the embryonic endolymphatic sac. Elucidating the mechanism of hearing loss may offer clues to potential therapeutic strategies.

Human cytomegalovirus (HCMV) and hearing impairment: infection of fibroblast cells with HCMV induces chromosome breaks at 1q23.3, between loci DFNA7 and DFNA49 -- both involved in dominantly inherited, sensorineural, hearing impairment

Human cytomegalovirus (HCMV) infection is the most common congenital infection in developed countries and is responsible for a substantial fraction of sensorineural hearing impairment (SNHI) in children. The risk of hearing impairment is associated with viral load in urine and blood collected during the first postnatal month. However, although inner ear abnormalities are observed in some children with HCMV-induced SNHI, the exact mechanism whereby congenital HCMV infection causes hearing impairment is unknown. Earlier studies using standard cytogenetic mapping techniques showed that infection of S-phase human fibroblast cells with HCMV resulted in two specific, site-directed, chromosome breaks at band positions 1q21 and 1q42 which include loci involved in dominantly and recessively inherited hearing impairment, respectively. These findings suggested that cells infected with HCMV might provide a reservoir for genetic damage and, in a clinical perspective, a scenario could be envisioned whereby hearing impairment could result from early DNA damage of dividing fetal cells rather than viral replication and cell lysis. In this work we demonstrate, using fine mapping techniques, that HCMV infection in S-phase fibroblast cells induces genetic damage at 1q23.3, within a maximal region of 37 kb, containing five low copy repeat (LCR) elements. The breakpoint is situated between two hearing impairment (HI) loci, DFNA49 and DFNA7, and in close proximity to the MPZ gene previously shown to be involved in autosomal dominant Charcot-Marie-Tooth syndrome (CMT1B) with auditory neuropathy.

Audiometric, clinical and educational outcomes in a pediatric symptomatic congenital cytomegalovirus (CMV) population with sensorineural hearing loss

OBJECTIVE

To correlate audiometric findings and outcomes with the clinical, radiological and educational findings in a symptomatic congenital cytomegalovirus (CMV) population with sensorineural hearing loss.

METHODS

A retrospective review of data from 21 symptomatic congenital CMV patients identified in a pediatric hearing impaired database of 1500 patients. Clinical data, audiometric thresholds and outcomes, radiographic abnormalities, communication and educational achievements were used as outcome measures.

RESULTS

Twenty-one patients were identified with symptomatic congenital CMV infection at birth; 5 with unilateral hearing loss and 16 with bilateral hearing loss. The median initial pure-tone average (PTA) for the 21 subjects was 86 dB and the median final PTA was 100 dB. Progression of hearing loss was seen in 9 patients (43%). Neurological and radiological sequelae of symptomatic CMV infection were seen in 81% of affected patients. Children with neurological dysfunction were significantly more likely to rely on special education (p = 0.045). There was a significant correlation between the severity of the initial PTA and the development of a progressive hearing loss (p = 0.0058). Initial hearing thresholds were significantly better in those children with a history of jaundice (p = 0.002), hepatosplenomegaly (HSM) (p = 0.022) and cerebral palsy (CP) (p = 0.013). There was a significant correlation between a less severe final PTA and the presence of CP (p = 0.005). A history of mental retardation in children was significantly associated with poorer communication skills (p = 0.043).

CONCLUSIONS

The severity of neurological manifestations in congenital symptomatic CMV infection was positively correlated with the need for total and manual communication and the reliance on special education. Statistical associations between clinical findings such as hepatic dysfunction, CP and hearing level were identified however plausible mechanisms explaining these associations remain ambiguous and are discussed in the context of this complex population of children with congenital symptomatic CMV.

Vestibular-evoked myogenic potentials in three patients with large vestibular aqueduct

An enlarged vestibular aqueduct (LVA) is a common congenital inner ear anomaly responsible for some unusual vestibular and audiological symptoms. Most of the cases show bilateral early onset and progressive hearing loss in children. The gross appearance on CT scan of the inner ear is generally normal. However, precise measurements of the inner ear components reveal abnormal dimensions, which may account for the accompanying auditory and vestibular dysfunction. Despite extensive studies on hearing and the vestibular apparatus, saccular function is not studied. To our knowledge this is the first report of saccular malfunction in three patients with LVA by means of vestibular evoked myogenic potentials. Conventional audiograms revealed bilateral severe sensorineural hearing loss in two patients and mixed type hearing loss in one patient. Two of the patients complained about vertigo and dizziness but vestibular assessments of the patients showed normal results. The diagnosis had been made by high-resolution CT scans and MR images of the skull that showed LVA in the absence of other anomalies. The VEMP threshold measured from the ear with LVA in two patients with unilateral enlargement of the vestibular aqueduct was 75-80 dB nHL whereas the threshold from normal ears was 95 dB nHL. The third patient with mixed type hearing loss and bilateral LVA had VEMP responses despite a big air-bone gap in the low frequency range. The VEMP in this patient was greater in amplitude and lower in threshold in the operated ear (the patient had a tympanoplasty which did not improve her hearing). These findings and results of other patients with Tullio phenomenon and superior semicircular canal dehiscence, who also showed lower VEMP threshold, confirmed the theory of a 'third window' that allows volume and pressure displacements, and thus larger deflection of the vestibular sensors, which would cause the vestibular organ to be more responsive to sound and pressure changes.

Vestibular disturbance in patients with large vestibular aqueduct syndrome (LVAS)

Large vestibular aqueduct syndrome (LVAS) is a common inner ear anomaly responsible for some unusual vestibular and audiological symptoms. The gross appearance of CT scan of the inner ear is generally normal. However, precise measurement of the inner ear components reveals abnormal dimensions, which may account for accompanying auditory or vestibular dysfunction. It has been reported that sudden increase in cerebrospinal fluid pressure can cause further deterioration of hearing due to transmission of pressure to the inner ear through the enlarged vestibular aqueduct. However, vestibular function is not often studied. In this report, audiovestibular function of 10 patients with large vestibular aqueducts was analysed and compared with the severity of the radiological deformity. The literature was reviewed and typical findings were discussed to emphasize varying aspects of audiovestibular function. It was found that some patients with LVAS have some spontaneous or provoked vestibular disturbance such as vertigo after watching revolving objects. The mean value of electronystagmographic abnormality in patients with hearing loss is greater than in patients with normal hearing. However, there is no statistical correlation between the level of hearing loss, electronystagmographic abnormality and severity of radiological deformity.

Progressive sensorineural hearing loss in childhood

A progressive sensorineural hearing loss in childhood, with an extremely variable prevalence (from 4% to 30%), has been reported in the literature. This wide range of reported figures could depend on the different criteria used for identifying the deterioration, the groups, and the examined age ranges. The most frequent etiology of progressive sensorineural hearing loss in childhood includes hereditary causes, both syndromic and nonsyndromic, and developmental and infectious causes, whereas metabolic, toxic, autoimmune, traumatic, and vascular etiologies are less common; however, the origin of the hearing impairment often remains unknown. The population for this study consisted of 178 children with bilateral sensorineural hearing loss who were examined between 1971 and 1993 using audiologic tests. Syndromal genetic hearing loss was excluded from the study. A progressive loss of acuity was found in 11 subjects, with a prevalence of 6.2%. The etiology was hereditary deafness in five patients, congenital infection in one, and congenital inner ear anomaly in another patient; in the last four children the etiology was unknown. Onset of deterioration was after 4 years of age in 73% of the patients. The progressive evolution was binaural in almost all patients (10 of 11) and asymmetric in most, with a tendency to a greater deterioration at the frequencies initially least affected.

Single gene influences on radiologically-detectable malformations of the inner ear

Inner ear malformations associated with hearing loss or vestibular dysfunction are discussed from the viewpoint of the etiologies of the malformation. Symptoms of classification of inner ear malformations are discussed. The significance of malformations of the cochlea and vestibular aqueduct to auditory function are discussed. Genetics features and characteristics of Branchio-oto-renal, Waardenburg's, Pendred's, DiGeorge's, Wildervanck, Fountain, and Treacher Collins syndromes are discussed in relation to ear abnormalities and hearing. Similar attention is given to genetic studies of nonsyndromic hearing loss.

Audiovestibular sequelae of congenital cytomegalovirus infection in 3 children presumably representing 3 symptomatically different types of delayed endolymphatic hydrops

Three cases of congenital cytomegalovirus (CMV) infection with long-term audiovestibular sequelae are presented. Case 1 had no hearing in one ear and severe progressive hearing loss in the other ear; he showed vestibular symptoms at the age of 4.5 years. Case 2 had severe but stationary hearing loss in one ear and showed hearing impairment symptoms in the other ear at 9-13 years of age. Case 3 did not have hearing impairment symptoms, or vestibular symptoms, but was found to have severe progressive hearing loss from the age of 15 months onwards, which led to profound deafness at the age of 2 years and vestibular areflexia at or before the age of 4 years. These cases may represent 3 symptomatically different types of delayed endolabyrinthine hydrops. Type 1 (ipsilateral hydrops) incorporates vestibular symptoms only because of a lack of hearing in the offending labyrinth. Type 2 (contralateral hydrops) incorporates hearing impairment symptoms only because of a lack of vestibular function on both sides and type 3 does not incorporate hearing impairment symptoms or vestibular symptoms (other than those relating to a complete lack of function). Given the present findings, those described by Weiss and Ronis (Trans. Pa. Acad. Opthalmol. Otolaryngol., 30 (1977) 52-54) in one case and other reported findings relating to histopathological or imaging methods in somewhat similar cases, it seems appropriate to include congenital CMV infection in the differential diagnosis of delayed endolymphatic hydrops.