Growth Hormone and the Auditory Pathway: Neuromodulation and Neuroregeneration.

Growth hormone (GH) plays an important role in auditory development during the embryonic stage. Exogenous agents such as sound, noise, drugs or trauma, can induce the release of this hormone to perform a protective function and stimulate other mediators that protect the auditory pathway. In addition, GH deficiency conditions hearing loss or central auditory processing disorders. There are promising animal studies that reflect a possible regenerative role when exogenous GH is used in hearing impairments, demonstrated in in vivo and in vitro studies, and also, even a few studies show beneficial effects in humans presented and substantiated in the main text, although they should not exaggerate the main conclusions.

Assessment of the latest NGS enrichment capture methods in clinical context.

Enrichment capture methods for NGS are widely used, however, they evolve rapidly and it is necessary to periodically measure their strengths and weaknesses before transfer to diagnostic services. We assessed two recently released custom DNA solution-capture enrichment methods for NGS, namely Illumina NRCCE and Agilent SureSelect(QXT), against a reference method NimbleGen SeqCap EZ Choice on a similar gene panel, sharing 678 kb and 110 genes. Two Illumina MiSeq runs of 12 samples each have been performed, for each of the three methods, using the same 24 patients (affected with sensorineural disorders). Technical outcomes have been computed and compared, including depth and evenness of coverage, enrichment in targeted regions, performance in GC-rich regions and ability to generate consistent variant datasets. While we show that the three methods resulted in suitable datasets for standard DNA variant discovery, we describe significant differences between the results for the above parameters. NimbleGen offered the best depth of coverage and evenness, while NRCCE showed the highest on target levels but high duplicate rates. SureSelect(QXT) showed an overall quality close to that of NimbleGen. The new methods exhibit reduced preparation time but behave differently. These findings will guide laboratories in their choice of library enrichment approach.

Knowledge-based analysis of functional impacts of mutations in microRNA seed regions.

MicroRNAs are a class of important post-transcriptional regulators. Genetic and somatic mutations in miRNAs, especially those in the seed regions, have profound and broad impacts on gene expression and physiological and pathological processes. Over 500 SNPs were mapped to the miRNA seeds, which are located at position 2-8 of the mature miRNA sequences. We found that the central positions of the miRNA seeds contain fewer genetic variants and therefore are more evolutionary conserved than the peripheral positions in the seeds. We developed a knowledgebased method to analyse the functional impacts of mutations in miRNA seed regions. We computed the gene ontology-based similarity score GOSS and the GOSS percentile score for all 517 SNPs in miRNA seeds. In addition to the annotation of SNPs for their functional effects, in the present article we also present a detailed analysis pipeline for finding the key functional changes for seed SNPs. We performed a detailed gene ontology graph-based analysis of enriched functional categories for miRNA target gene sets. In the analysis of a SNP in the seed region of hsa-miR-96 we found that two key biological processes for progressive hearing loss 'Neurotrophin TRK receptor signaling pathway' and 'Epidermal growth factor receptor signaling pathway' were significantly and differentially enriched by the two sets of allele-specific target genes of miRNA hsa-miR-96.

Epigenome-wide DNA methylation in hearing ability: new mechanisms for an old problem.

Epigenetic regulation of gene expression has been shown to change over time and may be associated with environmental exposures in common complex traits. Age-related hearing impairment is a complex disorder, known to be heritable, with heritability estimates of 57-70%. Epigenetic regulation might explain the observed difference in age of onset and magnitude of hearing impairment with age. Epigenetic epidemiology studies using unrelated samples can be limited in their ability to detect small effects, and recent epigenetic findings in twins underscore the power of this well matched study design. We investigated the association between venous blood DNA methylation epigenome-wide and hearing ability. Pure-tone audiometry (PTA) and Illumina HumanMethylation array data were obtained from female twin volunteers enrolled in the TwinsUK register. Two study groups were explored: first, an epigenome-wide association scan (EWAS) was performed in a discovery sample (n=115 subjects, age range: 47-83 years, Illumina 27 k array), then replication of the top ten associated probes from the discovery EWAS was attempted in a second unrelated sample (n=203, age range: 41-86 years, Illumina 450 k array). Finally, a set of monozygotic (MZ) twin pairs (n = 21 pairs) within the discovery sample (Illumina 27 k array) was investigated in more detail in an MZ discordance analysis. Hearing ability was strongly associated with DNA methylation levels in the promoter regions of several genes, including TCF25 (cg01161216, p = 6.6 × 10(-6)), FGFR1 (cg15791248, p = 5.7 × 10(-5) and POLE (cg18877514, p= 6.3 × 10(-5)). Replication of these results in a second sample confirmed the presence of differential methylation at TCF25 (p(replication)=6 × 10(-5)) and POLE (p(replication) =0.016). In the MZ discordance analysis, twins' intrapair difference in hearing ability correlated with DNA methylation differences at ACP6 (cg01377755, r= -0.75, p=1.2 × 10(-4)) and MEF2D (cg08156349, r= -0.75, p=1.4 × 10(-4)). Examination of gene expression in skin, suggests an influence of differential methylation on expression, which may account for the variation in hearing ability with age.

Linkage study and exome sequencing identify a BDP1 mutation associated with hereditary hearing loss.

Nonsyndromic Hereditary Hearing Loss is a common disorder accounting for at least 60% of prelingual deafness. GJB2 gene mutations, GJB6 deletion, and the A1555G mitochondrial mutation play a major role worldwide in causing deafness, but there is a high degree of genetic heterogeneity and many genes involved in deafness have not yet been identified. Therefore, there remains a need to search for new causative mutations. In this study, a combined strategy using both linkage analysis and sequencing identified a new mutation causing hearing loss. Linkage analysis identified a region of 40 Mb on chromosome 5q13 (LOD score 3.8) for which exome sequencing data revealed a mutation (c.7873 T>G leading to p.*2625Gluext*11) in the BDP1 gene (B double prime 1, subunit of RNA polymerase III transcription initiation factor IIIB) in patients from a consanguineous Qatari family of second degree, showing bilateral, post-lingual, sensorineural moderate to severe hearing impairment. The mutation disrupts the termination codon of the transcript resulting in an elongation of 11 residues of the BDP1 protein. This elongation does not contain any known motif and is not conserved across species. Immunohistochemistry studies carried out in the mouse inner ear showed Bdp1 expression within the endothelial cells in the stria vascularis, as well as in mesenchyme-derived cells surrounding the cochlear duct. The identification of the BDP1 mutation increases our knowledge of the molecular bases of Nonsyndromic Hereditary Hearing Loss and provides new opportunities for the diagnosis and treatment of this disease in the Qatari population.

The role of a family history in King Kopetzky Syndrome (obscure auditory dysfunction).

King Kopetzky Syndrome (KKS) is a common condition in which individuals with normal audiograms complain of hearing difficulties, particularly in noisy places. Several studies have shown many patients with KKS to have a family history of hearing problems. In 82 consecutive patients with KKS and normal middle ear function, we compared the performance of those with and without a family history of hearing impairment on a number of sensitized tests. Those with a family history were more likely to have notches on Audioscan testing (p < 0.005) and these notches were broader than those found in patients with no family history (p < 0.05). There was also a tendency for those with a family history to be more likely to have notches on DPOAEs (p < 0.07), and the reproducibility of the TOAEs was poorer in those with a family history. Psychological testing showed males with a family history to have higher scores on free-floating anxiety (p < 0.01) and obsessionality (p < 0.05).

A stepwise approach to the diagnosis and treatment of hereditary hearing loss.

What To Do Do suspect a genetic cause in all cases of hearing loss. Do develop a working knowledge of common types of HHI that you may draw on to aid in diagnosis. Do think of HHI when the audiogram reveals a hearing loss with a "cookie bite" configuration. Do refer the infant to a geneticist in cases where you suspect a syndromic HHI, a nonsyndromic HHI, and in cases of "cryptogenic" hearing loss where an underlying HHI may be present. Often, the associated symptoms are subtle and best detected by a professional who deals with these issues on a daily basis. Do get the infant or family plugged into an audiologist or otolaryngologist and speech pathologist who will preferably work as a team to maximize aural rehabilitation and ensure serial follow-up. It is never too early to fit a child with hearing aids. Do refer to the HHIRR center at Boys Town. Do refer to the correct "deaf" organization or "blind-deaf" organization. Do think about working up other siblings or family members. Do keep in mind that some members of the "deaf society" may regard deafness as an alternative lifestyle and may not be amenable to their child's referral for additional workup and aural rehabilitation. What Not To Do Do not assume the child is deaf and nothing can be done. Do not wait until the child is older to refer to an otolaryngologist, speech therapist, and audiologist. Do not order a sonogram. Do not order a temporal bone CT scan on newborns. Do not forget about other siblings who may have a similar pathology. Do not forget that some forms of HHI can present beyond infancy. The pediatrician is the front line and can play a major role in the diagnosis, workup, and treatment of HHI. Armed with the proper degree of suspicion, careful elicitation of family history, meticulous physical examination, evaluation of the audiogram, and adequate fund of knowledge of common types of genetic deafness, the pediatrician can make a timely diagnosis and appropriate referrals. This avoids delay in detection of significant hearing impairment and the associated lack of essential skills in speech, language, and social interaction. No child is too young to have some type of hearing assessment. Early detection and intervention are best done with a multidisciplinary team approach with a neonatologist or pediatrician, audiologist, speech therapist, and otolaryngologist. In the future, blood tests using genetic probes may be available to screen for many types of HHI.

Localization of a gene for non-syndromic hearing loss (DFNA5) to chromosome 7p15.

Progressive hearing loss affects approximately 50% of the elderly by the age of 80, and is most likely caused by an interaction of genetic and environmental factors. Identification of the genes responsible for hereditary hearing loss is therefore important. Families with pure genetic degenerative hearing disorders may be helpful as the same genes may be also involved in age-related hearing loss in general. In this study we have performed a genome search in an extended Dutch family with autosomal dominant progressive hearing loss starting in the high frequencies. The gene causing hearing loss in this family was localized to the short arm of chromosome 7, in a 15 cM interval between markers D7S493 and D7S632.

Inherited hearing defects in mice.

Mouse mutants with hearing impairment are useful for elucidating the pathological processes underlying auditory system defects, as well as for understanding the normal process of auditory development and sensory transduction. Deaf mouse mutants are also valuable for identifying the responsible genes by positional cloning, and are used to expedite the search for genes involved in human deafness. The distribution of candidate genes for deafness across the mouse genome is presented, together with a summary of the key features of the mutants involved. Genetic defects affecting hearing can be grouped into broad categories according to their pathological features. These categories include middle ear defects, morphogenetic inner ear defects, central auditory system defects, peripheral neural defects, neuroepithelial defects, cochleo-saccular defects, and late onset hearing loss. The biological features and molecular basis of each type of hearing impairment are described. Finally, the effects of mutations in orthologous genes involved in the auditory system in humans and mice are compared.