Are MYO1C and MYO1F associated with hearing loss?

The role of myosins in the pathogenesis of hearing loss is well established: five genes encoding unconventional myosins and two genes encoding nonmuscle conventional myosins have so far been described to be essential for normal auditory function and mutations in these genes associated with hearing impairment. To better understand the role of this gene family we performed a mutational screening on two candidate genes, MYO1C and MYO1F, analyzing hundreds of patients, affected by bilateral sensorineural hearing loss and coming from different European countries. This research activity led to the identification of 6 heterozygous missense mutations in MYO1C and additional 5 heterozygous missense mutations in MYO1F. Homology modelling suggests that some of these mutations could have a potential influence on the structure of the ATP binding site and could probably affect the ATPase activity or the actin binding process of both myosins. This study suggests a role of the above mentioned myosin genes in the pathogenesis of hearing loss.

Modeling the effect of 3 missense AGXT mutations on dimerization of the AGT enzyme in primary hyperoxaluria type 1.

INTRODUCTION: Mutations of the AGXT gene encoding the alanine:glyoxylate aminotransferase liver enzyme (AGT) cause primary hyperoxaluria type 1 (PH1). Here we report a molecular modeling study of selected missense AGXT mutations: the common Gly170Arg and the recently described Gly47Arg and Ser81Leu variants, predicted to be pathogenic using standard criteria. METHODS: Taking advantage of the refined 3D structure of AGT, we computed the dimerization energy of the wild-type and mutated proteins. RESULTS: Molecular modeling predicted that Gly47Arg affects dimerization with a similar effect to that shown previously for Gly170Arg through classical biochemical approaches. In contrast, no effect on dimerization was predicted for Ser81Leu. Therefore, this probably demonstrates pathogenic properties via a different mechanism, similar to that described for the adjacent Gly82Glu mutation that affects pyridoxine binding. CONCLUSION: This study shows that the molecular modeling approach can contribute to evaluating the pathogenicity of some missense variants that affect dimerization. However, in silico studies--aimed to assess the relationship between structural change and biological effects--require the integrated use of more than 1 tool.

Genetic variant of C1GalT1 contributes to the susceptibility to IgA nephropathy.

BACKGROUND: IgA nephropathy (IgAN) is a common form of primary glomerulonephritis characterized by diffuse glomerular mesangial IgA1 deposition that leads to mesangial proliferation and chronic glomerular inflammation. Analyses of serum IgA1 from IgAN patients revealed an abnormal galactosylation of the O-linked carbohydrate moieties of IgA that may be a result of altered activity of core 1 beta1,3-galactosyltransferase (C1GalT1). To evaluate the association between C1GalT1 single nucleotide polymorphisms (SNPs) and IgAN, we performed a case control study on cohorts from the Italian population. METHODS: We sequenced C1GalT1 coding and promoter regions in 284 IgAN patients and 210 healthy controls. The functional role of 3' untranslated region (3'UTR) SNPs was studied using electrophoretic mobility shift assays and real-time quantitative PCR. RESULTS: We analyzed 8 SNPs in the C1GalT1 gene: 5 SNPs were in the promoter region and 3 SNPs in the 3'UTR. The allele 1365G in the 3'UTR was significantly more frequent in IgAN patients than in healthy controls. CONCLUSION: The 1365G allele and 1365G/G genotype seem to confer susceptibility to IgAN.

Age-related hearing loss in four Italian genetic isolates: an epidemiological study.

The objective of this study was to estimate the prevalence of hearing impairment in four genetically isolated Italian villages (Carlantino, Campora, Gioi-Cardile, and Stoccareddo), 1682 subjects were recruited from all the individuals participating in a multidisciplinary study. They underwent otoscopy and pure-tone audiometry and completed a questionnaire. The audiological data show that the percentage of impaired people increases with age and in particular becomes relevant aged over 40. For this reason we decided to compare the PTA values of individuals aged 40 or older. The PTA values of Stoccareddo and Carlantino are statistically different from PTAs of the other villages. Campora and Gioi-Cardile, both located within the Cilento National Park, have similar middle-low frequency PTA values while some differences are present at high frequencies. Using pedigrees it was possible to calculate the heritability of the trait. For Carlantino and Gioi-Cardile the percentage of the phenotype variation attributable to genetic variation is not significant, while for Campora the heritability value is 0.49 (p = 0.01) suggesting that genetic factors may have an important role.

Lactase non-persistent genotype distribution in Italy.

BACKGROUND: Adult-type hypolactasia is a frequent condition of lactose malabsorption; in Europe the distribution of adult-type hypolactasia have been shown to display a North-South gradient. Genotyping for LCT-13910 C>T polymorphism has been proposed as a useful diagnostic marker of adult-type hypolactasia. Data concerning lactase non-persistent genotype distribution in Italy are confused and not well characterized. The aim of this study was to determine the prevalence of CC-genotype corresponding to lactase non-persistence in Italian population. METHODS: We genotyped 1312 adult Italian subjects for LCT-13910 C>T polymorphism by KASPar chemistry (KBioscience Ltd., Hoddesdon, England, UK). RESULTS: The frequency of the lactase non-persistence genotype of our sample was 62.3% that was higher than the values published for adult hypolactasia in Italy. In our study a frequency of 58.6%, 74.1% and 67.1% was detected in the three main macro-regions of Italy (North, Center, and South), respectively. CONCLUSIONS: For the first time we analyzed the distribution of the LCT-13910 CC genotype in a big population of Italian subjects. Our data did not validate the presence of a North-South gradient for adult hypolactasia along the Italian peninsula.

Five new OTOF gene mutations and auditory neuropathy.

OBJECTIVE: Purpose of this paper is to analyse OTOF gene in a series of subjects affected by auditory neuropathy. METHODS: Four children showing mild to profound prelingual deafness, confirmed by the absence of a clear and detectable responses at auditory brainstem responses (ABR), associated with the presence of bilateral OAE, were enrolled in the study. RESULTS AND CONCLUSIONS: Genetic analysis identified five new mutations (a nonsense, a small and a large deletion and two splicing site mutations), and one missense mutation (F1795C) previously described. These results further confirm the role of OTOF gene in auditory neuropathy. In the absence of a context of neurological syndrome, the combination of absent ABR and positive OAE responses should lead to an auditory neuropathy diagnosis and to a mutational screening in OTOF.

Vezatin, an integral membrane protein of adherens junctions, is required for the sound resilience of cochlear hair cells.

Loud sound exposure is a significant cause of hearing loss worldwide. We asked whether a lack of vezatin, an ubiquitous adherens junction protein, could result in noise-induced hearing loss. Conditional mutant mice bearing non-functional vezatin alleles only in the sensory cells of the inner ear (hair cells) indeed exhibited irreversible hearing loss after only one minute exposure to a 105 dB broadband sound. In addition, mutant mice spontaneously underwent late onset progressive hearing loss and vestibular dysfunction related to substantial hair cell death. We establish that vezatin is an integral membrane protein with two adjacent transmembrane domains, and cytoplasmic N- and C-terminal regions. Late recruitment of vezatin at junctions between MDCKII cells indicates that the protein does not play a role in the formation of junctions, but rather participates in their stability. Moreover, we show that vezatin directly interacts with radixin in its actin-binding conformation. Accordingly, we provide evidence that vezatin associates with actin filaments at cell-cell junctions. Our results emphasize the overlooked role of the junctions between hair cells and their supporting cells in the auditory epithelium resilience to sound trauma.