Hereditary deafness: the genetic defects unravelled
Hannie Kremer (PI, ENT Department and Genetics Department)(Supervisor), Margit Schraders (Postdoc), Jaap Oostrik (Research Technician), Ilse Feenstra (Clinical Geneticist; Genetics Department), Ronald Admiraal (Otorhinolaryngolist), Patrick Huygen (Senior Researcher), Dirk Kunst (Otorhinolaryngologist), Ronald Pennings (Otorhinolaryngologist), Celia Zazo Seco (PhD student), Eline van Beelen (PhD student), Anne Oonk (PhD student).
Hereditary hearing impairment (or deafness) is among the most common monogenic disorders but can also be multifactorial as is the case for age-related hearing loss. Clinical and genetic heterogeneity of hearing impairment is enormous. We largely concentrate on the genetics of nonsyndromic deafness. Dominant, recessive, X-linked, Y-linked and mitochondrial inheritance patterns can be seen. Although more than 60 deafness genes are known already, it is estimated that more than hundred additional genes await identification. The aim of our studies is to identify genetic defects that underlie hereditary hearing impairment in the Netherlands and to unravel the molecular pathogenesis. To reach this goal, we include families from Pakistan and Turkey via collaborations with researchers in these countries. Hearing impairment often has a genetic cause also when there is only one hearing impaired individual in a family. Therefore, we study hearing impairment in families and in single cases. Linkage analysis, homozygosity mapping, and whole exome sequencing are performed and combined by using state-of-the-art techniques. Clinical characterization of the hearing loss in families enables us to establish genotype-phenotype correlations for hearing loss. The function of novel deafness genes is unraveled by studying the encoded protein with several techniques including the search for interaction partners. Identification of deafness genes facilitates adequate counseling of patients and their families and provides knowledge on inner ear function. Furthermore, it will provide handles for the development of future therapy. The research is a close collaboration between the ENT department and the departments of Human Genetics.
A comprehensive overview of genes involved in hearing impairment can be found at Hereditaryhearingloss.org
. The structure and function of the inner ear is extensively illustrated at Cochlear.com
Usher Syndrome: Genetics, Functional Genomics and Therapeutic Strategies
Hannie Kremer (PI, ENT Department and Genetics Department)(Supervisor), Erwin van Wijk (Postdoc), Theo Peters (Postdoc), Erik de Vrieze (Postdoc), Margo Dona (PhD student), Ralph Slijkerman (PhD student), Lisette Hetterschijt (Research Technician), Ronald Pennings (Otorhinolaryngologist), Bas Hartel (PhD student), Ronald Roepman (Molecular Biologist; Genetics Department), Jan Keunen (Ophthalmologist; Dept Ophthalmology), Helger Yntema (Clinical Molecular Geneticist; Genetics Department).
Patients suffering from Usher syndrome (USH) live an isolated life in a society that is based on fast communication and mobility. USH is a severe genetic disorder characterized by hearing impairment, occasionally vestibular impairment, and progressive retina degeneration. The hearing loss can be partly compensated by providing patients with hearing aids or cochlear implants but for the loss of vision currently no treatment is available. However, since the retina degeneration is slowly progressive, there is a time window for therapeutic intervention. Usher syndrome type IIa (USH2a), the most common type, is caused by mutations in the USH2A gene. Other genes involved in Usher syndrome are MYO7A, USH1C, CDH23, PCDH15 and USH1G (type I), GPR98 and DFNB31 (type II) and USH3A (type III). Also, defects in the USH2A gene are an important cause of non-syndromic retinitis pigmentosa. Usher proteins co-function in a protein network which explains why defects in genes encoding functionally different proteins are causative for one and the same disorder. We have a specific interest in the USH2A protein and whirlin.
Our Usher syndrome research focuses on two lines of research:
1) Unravelling the pathogenic mechanisms underlying the disorder;
2) Therapeutic development.
Recently, we have shown that NINL, which we identified as an interaction partner of USH2A, connects proteins involved in different retinal degeneration disorders (Usher syndrome, Leber congenital amaurosis and Joubert syndrome). This suggests an overlap in the molecular pathogenesis of these disorders. Further unravelling of the USH protein network is ongoing by using yeast two-hybrid screening and tandem affinity purification (TAP). The mechanisms of hearing impairment in Usher syndrome are (at least partly) understood. Those of retinal degeneration in Usher syndrome are largely unknown but the localization of the Usher proteins in the region of the connecting cilium of photoreceptor cells suggests that dysfunction of this structure which heavily functions in transport, is involved.
The therapeutic potential of three strategies is currently being explored: antisense oligonucleotide (AON)-based therapy, gene augmentation therapy using mini-genes, and interfering with the USH disease mechanism using chemical compounds. For further information please visit our EUR-USH consortium website: http://eur-ush.eu/.
To assess the efficacy of potential therapies at the level of the organism, animal models are needed. Although mutant mouse models are commonly used to study inherited disorders, in several cases the retinal phenotype in these models does not mimic that of patients with mutations in the orthologous gene (e.g. Ush2a knock-out mice). Zebrafish has emerged as a pre-eminent model for studying inherited retinal disease. They are easy to genetically manipulate, have a retinal structure comparable to humans, and are ideal for our initial studies. To evaluate the therapeutic potential of our different strategies in vivo, we therefore aim to generate and characterize zebrafish models for a selection of frequently found Usher syndrome-causing mutations.
Our lab has ample experience in guiding Master and Bachelor students. Frequently used techniques include molecular cloning, DNA, RNA or protein analysis/interactions, immunohistochemistry, cell culture and in vivo zebrafish studies (e.g. Crispr/Cas9, morpholino-induced knockdown studies or electron/fluorescence microscopy). If you are interested, please send your curriculum vitae and motivation letter to Dr. Arjan de Brouwer (Arjan.deBrouwer@radboudumc.nl) and ask for the internship possibilities.
Dirk Kunst (ENT consultant), Ronald Pennings (ENT consultant), Ronald Admiraal (ENT consultant), Hannie Kremer (Molecular geneticist), Ad Snik (Audiologist), Joop Leijendeckers (Audiologist), Ilse Feenstra (Clinical Geneticist, Genetics department), Lies Hoefsloot (Clinical Molecular Geneticist, Genetics department), Berit Verbist (Radiologist, Radiology department), Emmanuel Mylanus (ENT consultant), Patrick Huygen (Senior Researcher), Cor Cremers (ENT consultant), Eline van Beelen (PhD student), Anne Oonk (PhD student), Josephine van Nierop (PhD student), Loes Temmink (Research secretary)
Our clinical otogenetics team studies patients and families with hereditary hearing impairment already for more than thirty years, long before the first deafness gene was cloned in 1995. Our aim is to characterize the phenotype of specific genetic types of hearing impairment in order to improve counseling of our patients. We measure the severity and progression of hearing impairment via pure tone audiograms, and speech perception tests. We evaluate a possible association with other clinical symptoms and we look for optimal ways of rehabilitation (f.e. cochlear implantation).
Our studies are not only essential to the identification of novel deafness genes (Molecular Otogenetics) but also to obtain thorough insight in the clinical presentation. Hereditary hearing impairment is genetically extremely heterogeneous, which hampers a fast genetic diagnosis. Proper clinical evaluation of inherited hearing impairment can guide genetic screening and therefore is cost-effective as well. Evaluations of the phenotype are being conducted by cross-sectional as well as longitudinal statistical analyses of pure tone and speech audiometry. From these analyses, audioprofiles are constructed which we call Age-Related Typical Audiograms (ARTA) that depict the progression of hearing impairment over decade steps. Psychophysical tests are applied in order to further distinguish different genetic types of hearing impairment from each other and to enhance our insight into the underlying inner ear defects.
Our main topics of research are:
- Autosomal dominantly inherited hearing loss
- Autosomal recessively inherited hearing loss
- Turner syndrome
- Usher syndrome
- Congenital middle and external ear anomalies
- Cochlear implantation in hereditary hearing loss publications