Etiologic and diagnostic evaluation: algorithm for severe to profound sensorineural hearing loss in Brazil.

OBJECTIVE: Evaluation of the effectiveness of imaging and genetic testing, and establishment of a cost-effective diagnostic protocol for the etiologic diagnosis of sensorineural hearing loss (SNHL) in Brazil. DESIGN: Prospective cohort study. STUDY SAMPLE: Analysis of 100 unrelated Brazilian patients with severe to profound bilateral SNHL submitted to cochlear implant (CI) between 2002 and 2010 at the University of Campinas hospital. The study was based upon three groups: individuals with congenital, progressive, and sudden SNHL. RESULTS: After the diagnostic investigation, the number of cases with unknown etiology was reduced from 72 to 42 (a 42% reduction); 25% of cases were due to environmental factors, 19% to genetic causes, and 14% to inner-ear abnormalities or other clinical features. The genetic and imaging findings contributed to the diagnosis of SNHL in 19% and 20% of the cases analysed, respectively. Molecular testing mainly contributed to the diagnosis of patients with congenital SNHL, while the contribution of radiologic examination was higher for individuals with progressive or sudden SNHL. A sequential diagnostic protocol was proposed based on these data. CONCLUSIONS: The proposed diagnostic workup algorithm could provide better optimization of etiologic diagnosis, as well as reduced costs, compared to a simultaneous testing approach.

Molecular analysis of SLC26A4 gene in patients with nonsyndromic hearing loss and EVA: identification of two novel mutations in Brazilian patients.

UNLABELLED: The SLC26A4 gene has been described as the second gene involved in most cases of sensorineural non-syndromic hearing loss, since the first is the GJB2 gene. Recessive mutations in the SLC26A4 gene encoding pendrin, an anion transporter, are responsible for non-syndromic hearing loss associated with an enlarged vestibular aqueduct (EVA) and Pendred syndrome, which causes early hearing loss and affects the thyroid gland. Typically, the hearing loss is profound and prelingual. However, in some individuals, hearing impairment may develop later in childhood and then progress. Over 200 different SLC26A4 mutations have been reported, with each ethnic population having its own distinctive mutant allele series including a few prevalent founder mutations. OBJECTIVE: Perform the screening of the 20 coding exons of SLC26A4 gene in Brazilian deaf individuals with EVA. PATIENTS AND METHODS: Among the 23 unrelated non-syndromic hearing loss Brazilian patients with EVA, in whom no deafness-causing mutations of the GJB2 gene, the direct sequencing was performed to screen the 20 exons and their flanking regions of the SLC26A4 gene. RESULTS: The sequencing results revealed 9 cases (39%) carrying 13 different SLC26A4 mutations, including 11 known mutations (279delT, V138F, T193I, IVS8+1G>A, T410M, Q413R, R409H, L445W, IVS15+5G>A, V609G, and R776C) and 2 novel mutation (G149R and P142L). CONCLUSION: The SLC26A4 mutations have a high carrying rate in non-syndromic hearing loss Brazilian patients. The identification of a disease-causing mutation can be used to establish a genotypic diagnosis and provide important information to the patients and their families.

Study of modifiers factors associated to mitochondrial mutations in individuals with hearing impairment.

Hearing impairment is the most prevalent sensorial deficit in the general population. Congenital deafness occurs in about 1 in 1000 live births, of which approximately 50% has hereditary cause in development countries. Non-syndromic deafness can be caused by mutations in both nuclear and mitochondrial genes. Mutations in mtDNA have been associated with aminoglycoside-induced and non-syndromic deafness in many families worldwide. However, the nuclear background influences the phenotypic expression of these pathogenic mutations. Indeed, it has been proposed that nuclear modifier genes modulate the phenotypic manifestation of the mitochondrial A1555G mutation in the MTRNR1 gene. The both putative nuclear modifiers genes TRMU and MTO1 encoding a highly conserved mitochondrial related to tRNA modification. It has been hypothesizes that human TRMU and also MTO1 nuclear genes may modulate the phenotypic manifestation of deafness-associated mitochondrial mutations. The aim of this work was to elucidate the contribution of mitochondrial mutations, nuclear modifier genes mutations and aminoglycoside exposure in the deafness phenotype. Our findings suggest that the genetic background of individuals may play an important role in the pathogenesis of deafness-associated with mitochondrial mutation and aminoglycoside-induced.

Interaction between audiology and genetics in the study of a family: the complexity of molecular diagnosis and genetic counseling.

UNLABELLED: Hearing loss is a multifaceted condition with many etiologies, among which genetic mutation is. Therefore, it is important to connect audiological investigation to etiological diagnosis. AIM: this study aims to establish the audiological and genetic profiles of three non-syndromic children with sensorineural hearing loss. MATERIALS AND METHOD: three brothers aged 3, 5 and 16 were enrolled in this study. They were submitted to behavioral and electrophysiological hearing tests and molecular studies. RESULTS: the hearing tests showed moderate to moderately severe bilateral symmetric sensorineural hearing loss and an accentuated descending slope. Transient and Distortion Product Otoacoustic emissions were absent in the two younger children. ABR showed a bilateral moderately severe to severe sensorineural hearing loss. P300 showed bilateral normal latencies in the older brother. Molecular tests showed that the two younger children were heterozygote for mutation 35delG on gene GJB2. CONCLUSION: The combination of speech and hearing tests and genetic analysis allows for the etiologic diagnosis of seemingly similar hearing loss cases, which however display different genetic backgrounds. Molecular studies must be comprehensive enough to avoid precipitated diagnosis which may impair genetic counseling.