Genetic and clinical heterogeneity in Meniere's disease

A Drosophila model for Meniere's disease: Dystrobrevin is required for support cell function in hearing and proprioception

Meniere's disease (MD) is an inner ear disorder characterised by recurrent vertigo attacks associated with sensorineural hearing loss and tinnitus. Evidence from epidemiology and Whole Exome Sequencing (WES) suggests a genetic susceptibility involving multiple genes, including α-Dystrobrevin (DTNA). Here we investigate a Drosophila model. We show that mutation, or knockdown, of the DTNA orthologue in Drosophila, Dystrobrevin (Dyb), results in defective proprioception and impaired function of Johnston's Organ (JO), the fly's equivalent of the inner ear. Dyb and another component of the dystrophin-glycoprotein complex (DGC), Dystrophin (Dys), are expressed in support cells within JO. Their specific locations suggest that they form part of support cell contacts, thereby helping to maintain the integrity of the hemolymph-neuron diffusion barrier, which is equivalent to a blood-brain barrier. These results have important implications for the human condition, and notably, we note that DTNA is expressed in equivalent cells of the mammalian inner ear.

Effects of short- and long-term exposure to air pollution and meteorological factors on Meniere's disease

The association between air pollutants and Meniere’s disease has not been explored. The present study investigated the relationship between meteorological factors and air pollutants on Meniere’s disease. Participants, aged ≥ 40 years, of the Korean National Health Insurance Service-Health Screening Cohort were included in this study. The 7725 patients with Meniere’s disease were matched with 30,900 control participants. The moving average meteorological and air pollution data of the previous 7 days, 1 month, 3 months, and 6 months before the onset of Meniere’s disease were compared between the Meniere’s disease and control groups using conditional logistic regression analyses. Additional analyses were conducted according to age, sex, income, and residential area. Temperature range; ambient atmospheric pressure; sunshine duration; and levels of SO₂, NO₂, O₃, CO, and PM₁₀ for 1 month and 6 months were associated with Meniere’s disease. Adjusted ORs (odds ratios with 95% confidence interval [CI]) for 1 and 6 months of O₃ concentration were 1.29 (95% CI 1.23–1.35) and 1.31 (95% CI 1.22–1.42), respectively; that for the 1 and 6 months of CO concentration were 3.34 (95% CI 2.39–4.68) and 4.19 (95% CI 2.79–6.30), respectively. Subgroup analyses indicated a steady relationship of O₃ and CO concentrations with Meniere’s disease. Meteorological factors and air pollutants were associated with the rate of Meniere’s disease. In particular, CO and O₃ concentrations were positively related to the occurrence of Meniere’s disease.

Are viral-infections associated with Ménière's Disease? A systematic review and meta-analysis of molecular-markers of viral-infection in case-controlled observational studies of MD

Despite considerable research, it remains controversial as to whether viral-infections are associated with Meniere’s Disease (MD), a clinically heterogeneous set of chronic inner-ear disorders strongly associated with endolymphatic hydrops. Here, we investigated whether viral-infections are associated with MD through a systematic review and meta-analysis of observational clinical studies using molecular-diagnostics. Eligible for inclusion were case-controlled studies which ascertained molecular-determinants of past or present viral-infection through either viral nucleic acids or host serological marker in MD cases and non-MD controls. Across online databases and grey literature, we identified 210 potentially relevant articles in the English language, from which a total of 14 articles fully satisfied our eligibility criteria such that meta-groups of 611 MD-cases and 373 controls resulted. The aggregate quality of the modest-sized (14 studies) body of evidence was limited and varied considerably with regards to participant selection, matching, and ascertainment(s) and determinant(s) of viral-infection. Most data identified concerned the human cytomegalovirus (CMV), and meta-analysis of eligible studies revealed that evidence of CMV-infection was associated approximately three-fold with MD compared to controls, however the timing of the infections was indeterminate as the pooled analyses combined antiviral serological markers with viral nucleic acid markers. No association was found for any of HSV-1, -2, VZV, or EBV. Associative analyses of any viral species not aforementioned were precluded by limited data, and thus potential associations between other viral species and MD, especially other than Herpesviridae, are yet to be characterised. Overall, we have found a small association between CMV-infection and MD, however it is to be determined for what sub-groups of MD this finding may be relevant, and ideally the reported association remains would be reproduced by a greater volume of higher quality evidence.

Ménière's Disease: Molecular Analysis of Aquaporins 2, 3 and Potassium Channel KCNE1 Genes in Brazilian Patients

OBJECTIVES

Ménière's disease (MD) is a complex disease of unknown etiology characterized by a symptomatic tetrad of vertigo, hearing loss, tinnitus, and aural fullness. In addition to factors related to homeostasis of the inner ear, genetic factors have been implicated in its pathophysiology, including genes related to the transport of water and ionic composition maintenance of the endolymph, such as the aquaporin genes AQP2 and AQP3, and the potassium channel gene KCNE1. The aim of this study was to identify polymorphisms of these genes and determine their association with clinical characteristics of patients with MD.

DESIGN

A case-control genetic association study was carried out, including 30 patients with definite Ménière's disease and 30 healthy controls. The coding regions of the target genes were amplified from blood samples by polymerase chain reaction (PCR), followed by direct sequencing. The associations of polymorphisms with clinical characteristics were analyzed with logistic regression.

RESULTS

Five polymorphisms were identified: rs426496 in AQP2; rs591810 in AQP3; and rs1805127, rs1805128, and rs17173510 in KCNE1. After adjustment, rs426496 was significantly associated with tinnitus during the initial crisis and with altered electronystagmography, and rs1805127 was significantly associated with nephropathy.

CONCLUSIONS

The genetic variant rs426496 in AQP2; rs591810 in AQP3 and rs1805127, rs1805128, and rs17173510, in KCNE1 were found in patients with Ménière's disease. The polymorphism rs426496, in AQP2, is associated with tinnitus at the onset of Ménière's disease and altered electronystagmography. In addition, rs1805127, in KCNE1, is associated with the presence of nephropathy.

The genetics of Ménière's disease

Our understanding of the genetic basis of Ménière’s disease (MD) is still limited. Although the familial clustering and the geographical and racial differences in incidence strongly suggest a certain role for genetic factors in the development of MD, no convincing evidence for an association with any gene exists, at present. In this review, starting from rational bases for a genetic approach to MD, we explored the numerous reports published in literature and summarize the recent advances in understanding of the genetic fundaments of the disease.

Identification of two novel mutations in FAM136A and DTNA genes in autosomal-dominant familial Meniere's disease

Meniere's disease (MD) is a chronic disorder of the inner ear defined by sensorineural hearing loss, tinnitus and episodic vertigo, and familial MD is observed in 5-15% of sporadic cases. Although its pathophysiology is largely unknown, studies in human temporal bones have found an accumulation of endolymph in the scala media of the cochlea. By whole-exome sequencing, we have identified two novel heterozygous single-nucleotide variants in FAM136A and DTNA genes, both in a Spanish family with three affected cases in consecutive generations, highly suggestive of autosomal-dominant inheritance. The nonsense mutation in the FAM136A gene leads to a stop codon that disrupts the FAM136A protein product. Sequencing revealed two mRNA transcripts of FAM136A in lymphoblasts from patients, which were confirmed by immunoblotting. Carriers of the FAM136A mutation showed a significant decrease in the expression level of both transcripts in lymphoblastoid cell lines. The missense mutation in the DTNA gene produces a novel splice site which skips exon 21 and leads to a shorter alternative transcript. We also demonstrated that FAM136A and DTNA proteins are expressed in the neurosensorial epithelium of the crista ampullaris of the rat by immunohistochemistry. While FAM136A encodes a mitochondrial protein with unknown function, DTNA encodes a cytoskeleton-interacting membrane protein involved in the formation and stability of synapses with a crucial role in the permeability of the blood-brain barrier. Neither of these genes has been described in patients with hearing loss, FAM136A and DTNA being candidate gene for familiar MD.