The goal of the Laboratory of Molecular Genetics, Section on Human Genetics is to identify and study the function of mutated genes for human hereditary syndromic and nonsyndromic deafness. A new study begins with the ascertainment of large families in which deafness appears to be inherited either as a monogenic dominant or as monogenic recessive trait. We then search for linkage of the deafness to 950,000 SNP markers distributed across the human genome. During the past year we ascertained several large families segregating deafness, mapped novel deafness loci and have identified variants in the causative gene. Staff in the LMG have been working on the following projects, some of which were completed in the past year and have been published, are in press or are likely to be published in the near future. 1. Eleven years ago, DFNB32 was mapped to chromosome 1 by another research group, but the underlying gene was never reported. In five of our consanguineous families segregating recessively inherited nonsyndromic deafness linked to markers for the DFNB32 locus, we have identified three truncating mutations, a splice site mutation and a missense mutation in a gene in our refined DFNB32 interval. Ayesha Imtiaz, PhD, a fellow in the LMG, is exploring the function of the DFNB32 gene in the auditory system. Drs. Imtiaz and Belyantseva are using a conditional ko mouse of this gene that we have engineered to explore its function in the auditory system. As a collaboration with Dr. Katie Kindt, we have constructed zebrafish models of the DFNB32 gene to probe its function. A manuscript on this project was recently submitted. 2. The gene responsible for human deafness DFNB28 human deafness was identified as TRIOBP (Kitajiri et al., Cell, 2010). TRIOBP encodes three distinct proteins that arise from alternative splicing of TRIOBP transcripts. TRIOBP isoforms are referred to as TRIOBP-1, TRIOBP-4 and TRIOBP-5. Loss of TRIOBP-1 causes embryonic lethality in mouse. Simultaneous loss of TRIOBP4 and TRIOBP-5 causes deafness as a result of the inability of hair cells to develop stereocilia rootlets. Purified TRIOBP-4 tightly bundles F-actin typical of stereocilia rootlets. The individual function of TRIOBP-5 is not known. We have engineered mice that do not express function TRIOBP-5 and they are deaf but develop rootlets. The cause of deafness due to the loss of TRIBP-5 is being explored by Dr. Belyantseva in collaboration with Shin-ichiro Kitajiri, MD, PhD who is a PI of a laboratory in Japan. 3. The LMG is ascertaining families segregating Perrault Syndrome, which is characterized by deafness and female infertility. This project is an ongoing collaboration with William Newman, MD, PhD in Manchester, UK. We are also engineering mouse models of the human genes responsible for Perrault syndrome in order to understand their function in the auditory system. 4. Usher syndrome is genetically and clinically heterogeneous. In collaboration with Carmen Brewer, PhD, Andrew Griffith MD, PhD and Wadih Zein MD (NEI) we are studying the natural history of the visual, auditory and vestibular phenotypes of Usher syndrome subjects enrolled at the NIH Clinical Center. These Usher subjects have known biallelic molecular genetic variants determined by analyses conducted by staff in the LMG. As part of this project, several Usher-like subjects appear not to have pathogenic variants in the reported Usher genes. Whole exome sequencing (WES) is being undertaken in the LMG to identify novel Usher genes or possible novel regulatory variants of the reported Usher syndrome genes.
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