Margriet Verstreken

Hearing impairment and neurological dysfunction associated with a mutation in the mitochondrial tRNA^{Ser(UCN)} gene

We studied a large Dutch family with maternally inherited, progressive, sensorineural hearing loss in 27 patients. Only in a single family member was the hearing loss accompanied by neurological symptoms including ataxia and dysarthria. DNA analysis of the mitochondrial genome revealed the insertion of a C at nucleotide position 7472 in the tRNASer(UCN) gene (7472insC mutation). We determined the percentage of mutant DNA (heteroplasmy) in blood from all family members, and found no correlation between hearing loss and leucocyte heteroplasmy. The 7472insC mutation was previously identified in a smaller family from Sicily with sensorineural hearing loss in 9 family members, six of them also presenting neurologically with ataxia and myoclonus. The presence of the 7472insC mutation in two different pedigrees strongly supports its pathogenicity. However, the interfamilial difference in penetrance of the neurologic abnormalities is most likely to be strongly influenced by secondary factors different from the 7472insC mutation, as heteroplasmy or age of the patients were similar in both families. This mutation should therefore be analysed in families with maternally inherited hearing loss, irrespective of whether the hearing loss is non-syndromic or accompanied by neurologic abnormalities.

Otosclerosis: a genetically heterogeneous disease involving at least three different genes

Otosclerosis is caused by abnormal bone homeostasis of the otic capsule, resulting in hearing impairment in 0.3%-0.4% of the white population. The etiology of the disease remains unclear and environmental as well as genetic factors have been implicated. We localized the first autosomal-dominant locus to chromosome 15 in 1998 (OTSC1) in an Indian family and, recently, we reported the localization of a second gene for otosclerosis to a 16 cM interval on chromosome 7q (OTSC2). In this study, we recruited and analyzed nine additional families (seven Belgian and two Dutch families with 53 affected and 20 unaffected subjects) to investigate the importance of these loci in autosomal-dominant otosclerosis. We completed linkage analysis with three microsatellite markers of chromosome 15 (D15S652, D15S1004, D15S657) and five microsatellite markers of chromosome 7 (D7S495, D7S2560, D7S684, D7S2513, D7S2426). In two families, results compatible with linkage to OTSC2 were found, but in the seven remaining families OTSC1 and OTSC2 were excluded. Heterogeneity testing provided significant evidence for genetic heterogeneity, with an estimated 25% of families linked to OTSC2. These results indicate that, besides OTSC1 and OTSC2, there must be at least one additional otosclerosis locus.

A gene for autosomal dominant hearing impairment (DFNA14) maps to a region on chromosome 4p16.3 that does not overlap the DFNA6 locus

Non-syndromic hearing impairment is one of the most heterogeneous hereditary conditions, with more than 40 reported gene localisations. We have identified a large Dutch family with autosomal dominant non-syndromic sensorineural hearing impairment. In most patients, the onset of hearing impairment is in the first or second decade of life, with a slow decline in the following decades, which stops short of profound deafness. The hearing loss is bilateral, symmetrical, and only affects low and mid frequencies up to 2000 Hz. In view of the phenotypic similarities of this family with an American family that has been linked to chromosome 4p16.3 (DFNA6), we investigated linkage to the DFNA6 region. Lod score calculations confirmed linkage to this region with two point lod scores above 6. However, as haplotype analysis indicated that the genetic defect in this family is located in a 5.6 cM candidate region that does not overlap the DFNA6 region, the new locus has been named DFNA14.

Hereditary otovestibular dysfunction and Ménière's disease in a large Belgian family is caused by a missense mutation in the COCH gene

Objective To report the clinical, auditory, and vestibular characteristics of a nonsyndromic otovestibular dysfunction in a large Belgian family caused by a missense mutation of the DFNA9 gene: COCH. Study Design Retrospective study of the clinical, audiologic, and vestibular data of 60 genetically affected cases. Setting Tertiary referral center. Patients All members of a Belgian kindred who carry the genetic (P51S) defect linked to the inherited hearing and vestibular impairment. Interventions Diagnostic otologic, audiometric, and vestibular analysis and imaging. Main Outcome Measures Pure tone audiometry, supraliminary audiometry. and vestibular investigation. Results The autosomal dominant inherited impairment was characterized by peripheral degeneration of the inner ear, leading to total deafness and bilateral vestibular areflexia. Conclusions The genetically affected persons of a Belgian family shared a progressive sensorineural hearing loss starting between the third and sixth decade. Vestibular symptoms started at about the same age as the hearing loss. The vestibular symptoms consisted of instability in darkness, a tendency to fall sideways, light-headiness, a drunken feeling, and attacks of vertigo. Most of the patients reported tinnitus, and half of them reported pressure in the ears. Clinically, 9 of the 60 patients met the criteria for definite Ménières disease, and another 13 and 17 patients met the criteria for probable or possible Ménières disease, respectively. All 9 were older than the age of 35, but only 1 was older than 55 years, so more than 30% of the patients were between 35 and 55 years old. A specific pattern could be recognized in the evolution of the otovestibular impairment. Under the age of 35 years, almost all the affected family members had normal hearing, whereas above the age of 55 years, the hearing loss was at least moderate, and vestibular hypofunction occurred. In between, there was a transition period of two to three decades, when deterioration of the cochleovestibular function occurred, with a temporary audiometric and vestibular asymmetry.

Stapedotomy with Microdrill or Carbon Dioxide Laser: Influence on Inner Ear Function

Objectives: A prospective randomized audiological analysis of 336 otosclerosis operations was conducted to compare the evolution of bone conduction thresholds after primary stapedotomy with Two different techniques to open the footplate: microdrill and carbon dioxide laser stapedotomy. Methods: To monitor the inner ear function, we compared the preoperative bone conduction thresholds with the postoperative levels at day 2, week 2, week 6, and month 6. Evolution of the bone conduction was compared for the Two studied groups (laser versus microdrill). Results: An average bone conduction loss of 1.8 dB was measured at day 2 for the middle frequencies (0.5, 1, and 2 kHz). At 4 kHz, a bone conduction loss of 7 dB was found. The bone conduction thresholds measured in the first and second months after surgery showed a gradual recovery with overclosure as the end result. Conclusions: Our results confirm the transient depression of inner ear function in the immediate postoperative period, with recovery within the first weeks after surgery. In the studied population, no statistically significant difference was found between the Two techniques that were used to make the calibrated hole (laser versus microdrill). These results demonstrate that both techniques possess the same early effect regarding inner ear function. The authors hypothesize that an early inflammatory reaction could be the cause of the transient bone conduction shift.

DNA Diagnostics of Hereditary Hearing Loss: A Targeted Resequencing Approach Combined with a Mutation Classification System

Although there are nearly 100 different causative genes identified for nonsyndromic hearing loss (NSHL), Sanger sequencing‐based DNA diagnostics usually only analyses three, namely, GJB2, SLC26A4, and OTOF. As this is seen as inadequate, there is a need for high‐throughput diagnostic methods to detect disease‐causing variations, including single‐nucleotide variations (SNVs), insertions/deletions (Indels), and copy‐number variations (CNVs). In this study, a targeted resequencing panel for hearing loss was developed including 79 genes for NSHL and selected forms of syndromic hearing loss. One‐hundred thirty one presumed autosomal‐recessive NSHL (arNSHL) patients of Western‐European ethnicity were analyzed for SNVs, Indels, and CNVs. In addition, we established a straightforward variant classification system to deal with the large number of variants encountered. We estimate that combining prescreening of GJB2 with our panel leads to a diagnosis in 25%–30% of patients. Our data show that after GJB2, the most commonly mutated genes in a Western‐European population are TMC1, MYO15A, and MYO7A (3.1%). CNV analysis resulted in the identification of causative variants in two patients in OTOA and STRC. One of the major challenges for diagnostic gene panels is assigning pathogenicity for variants. A collaborative database collecting all identified variants from multiple centers could be a valuable resource for hearing loss diagnostics.

Involvement of T-cell receptor-\beta alterations in the development of otosclerosis linked to **OTSC2**

Otosclerosis is a common form of hearing loss, characterized by disordered bone remodeling in the otic capsule. Within the otosclerotic foci, several immunocompetent cells and immune-modulating factors can be found. Different etiological theories involving the immune system have been suggested. However, a genetic component is clearly present. In large otosclerosis families, seven autosomal-dominant loci have been found, but none of the disease-causing genes has been identified. This study focused on the exploration of the second otosclerosis locus on chromosome 7q34-36 (OTSC2), holding the T-cell receptor beta locus (TRB locus). A significantly lower T-cell receptor-β (TCR-β) mRNA expression and percentage of blood circulating TCR-αβ+ T cells was detected in OTSC2 patients compared with controls and patients with the complex form of the disease. Further analysis illustrated more significant disturbances in specific T-cell subsets, including an increased CD28null cell population, suggesting a disturbed T-cell development and ageing in OTSC2 patients. These disturbances could be associated with otosclerotic bone remodeling, given the known effects of immunocompetent cells on bone physiology. These data implicate the TRB locus as the causative gene in the OTSC2 region and represent an important finding in the elucidation of the disease pathology.

Transient Depression of Inner Ear Function after Stapedotomy: Skeeter versus CO2 Laser Technique

Performing stapes surgery for otosclerosis is known to be potentially irreversibly harmful to the inner ear function in about 1% of the cases. An early postoperative transient depression of the bone conduction thresholds is frequently detected after stapes surgery. The purpose of this study was to compare the evolution of bone conduction thresholds after primary stapedotomy with two different techniques: skeeter versus CO(2) laser stapedotomy. Audiological data of 336 otosclerosis operations performed by 2 surgeons between 1997 and 2003 were subjected to analysis. The calibrated hole in the footplate was performed randomly either with the skeeter drill or with the CO(2) laser. Preoperative bone conduction thresholds were compared with the postoperative levels (day 2-3, week 2, week 6 and month 6) in all patients. Evolution of the bone conduction was compared for the two studied subgroups (laser versus skeeter).

Bilateral otospongiosis and a unilateral vestibular schwannoma in a patient with Myhre syndrome.

Myhre syndrome is a rare disorder characterized by facial dysmorphism, short stature, generalized muscle hypertrophy, skeletal anomalies, and limited joint mobility (1). Hearing loss is frequently reported. The clinical findings have been described in 22 cases till date, and recently, a de novo dominant mutation in the SMAD4 gene was discovered in 19 patients (2). We report a case of Myhre syndrome with bilateral mixed hearing loss and bilateral fenestral otospongiosis on cone-beam computed tomography (CBCT). Magnetic resonance imaging (MRI) also revealed a nodule in the right internal auditory canal (IAC) compatible with a vestibular schwannoma (VS). No high resolution images of the temporal bone in patients with Myhre syndrome have been published, to the best of our knowledge.

Enhancement of the otic capsule in active retrofenestral otosclerosis.

Otosclerosis is the most common primary osseous lesion of the temporal bone. Diagnosis is based on clinical findings, audiometric testing, and family history, but there is an increasing demand for confirmation by medical imaging. Otosclerosis occurs in two phases: an early, active phase, during which bone resorption occurs (otospongiotic stage) and a later, inactive phase (sclerotic stage). In the active phase, osteolytic lesions appear in the endochondral layer of the otic capsule, resulting in disorganized formation of woven bone with marrow spaces containing osteoblasts, osteocytes, connective tissue, and blood vessels. The lytic areas are filled with soft tissue and are much less dense than normal labyrinthine bone. In time, lesions undergo diminution of cellularity, obliteration of blood vessels, remineralization, and reorganization to sclerotic lamellar bone. Both phases of the process may simultaneously be present. In otosclerosis, three major patterns of involvement are discerned: fenestral, retrofenestral, and mixed (1). In the fenestral type, lesions are located at the oval window (most commonly near the fissula ante fenestram, with possible involvement of the stapes footplate) and the lateral wall of the labyrinth (including the round window and promontory). The retrofenestral or cochlear type has typical irregular and discontinuous hypodensities caused by demineralization in the endochondral bone of the otic capsule. In the mixed type, there is involvement of the pericochlear otic capsule together with stapes footplate thickening. On high-resolution computed tomography, the spongiotic phase of retrofenestral otosclerosis presents as a partial or complete band of demineralization in the otic capsule surrounding the cochlea (so-called fourth coil or double-ring sign) (Fig. 1). Differential diagnosis includes osteogenesis imperfecta, labyrinthitis ossificans, and Paget’s disease (1). On magnetic resonance imaging (MRI), enhancement of the otic capsule has been reported in patients with active otosclerosis (2,3) and osteogenesis imperfecta Type I (4). Enhancement is presumably caused by pooling of contrast medium in the blood vessels and lacunae of the otospongiotic (active) foci (3,5). A correlation