Human Heredity November 2010 Erin Stafford 1

Introduction: What is Hereditary Deafness? Hereditary deafness is hearing loss that is passed down from parents to their children. Nonsyndromic hereditary deafness is hearing loss with no other medical conditions present other than deafness. I am interested in this topic because I know people that have nonsyndromic hereditary deafness that have hearing parents and hearing siblings. In researching the question, How is Deafness Inherited? I would like to find out why only some people in a family inherit deafness

How is Nonsyndromic Deafness Inherited? Most hereditary hearing loss is nonsyndromic. 80% of nonsyndromic hereditary hearing disorders are autosomal recessive. Autosomal recessive means that both parents must be carriers of the same gene mutation in order for a child to inherit the disorder. When both parents are carriers of the recessive gene mutation, there is a 25% chance that their child will inherit the disorder. Cummings, M. and Yashon, R. Human Genetics and Society. 3

Inheritance Pattern for Autosomal Recessive Gene Mutation Diagram: U.S. National Library of Medicine State of Missouri Dept.of Health 4

What Causes Nonsyndromic Hereditary Deafness? The genetic cause of hereditary deafness is from a mutation in the gene that makes a protein called Connexin 26. Colorado Neurological Inst. Diagram: Harvard Medical School Pamphlet: Hereditary Deafness This is a sensorineural deafness or nerve deafness. The cochlea cannot change sound waves into a signal that can be sent to the brain. 5

Genetic Link The genetic cause of nonsyndromic hereditary deafness is from mutations in the gene that makes Connexin 26, a protein. The gene that codes for Connexin 26 is called Gap Junction Beta 2 (GJB2). This gene is located on the long arm of chromosome 13. Diagram: National Library of Medicine, Genetics Home Reference Genetics: JGB2 National Library of Medicine Genetics Home Reference Genetics 6

Gap Junction Beta 2 (GJB2) People whose deafness is related to Connexin 26 have a variant of the GJB2 gene that does not make the protein Connexin 26. The protein Connexin 26 is present in the cochlea and outer skin cells. Connexin 26 helps in the formation of small channels called gap junctions between cells in the cochlea. These gap junctions serve as a way for the recycling of small potassium molecules, which are necessary for hearing. Without Connexin 26 protein, gap junctions do not form correctly, so potassium cannot be recycled in the cochlea. UCLA Deaf Genetics Project Diagram: University of Michigan 7

Genetic Testing Is Genetic testing for hereditary deafness available? Genetic testing for connexin 26 is available to children who are born deaf. Deafness and Hereditary Hearing Loss Overview Harvard Medical School Center for Hereditary Deafness How can genetic information help? Genetic testing allows an understanding of the hearing loss and what type of damage there is in the hearing system. Provides improved treatment choices. Can help in reproductive choices. 8

A Note About Genetic Testing It can be extremely disturbing for a parent to find that because of a gene mutation they carry their child is deaf. It is important to remember that gene mutations are common, and that no one is responsible for the genes they carry. Artwork : Concurring Opinions Harvard Medical School Center for Hereditary Deafness 9

Works Cited Barlow-Stewart, Kristine and Saleh, Mona. The Australasian Genetic Resource Book. Center for Genetics Education. June Web. 26 October Berke, Jamie. Cause of Hearing Loss-Genetics. About.com 19 March, Web. 26 October Cincinnati Children’s Hospital and Medical Center. Genetic Testing for Hearing Loss. Web. 26 October Colorado Neurological Institute. Therapy. Web. 26 October Deaf Genetics Project. University of California, LA. Web. 20 October “Genetic Deafness”. Genetic Alliance UK. July Web. 26 October Hegarty, Joseph L.Genetic Causes of Sensorineural Hearing Loss. Spring, CNI. Web. 26 October

Works Cited Moody, Stephanie A. and Strasnick, Barry. “Inner Ear, Genetic Sensorineural Hearing Loss”. Emedicine. June Web. 26 October “ Nonsyndromic Deafness”. Genetics Home Reference. U.S. National Library of Medicine. 24 October Web. 26 October, Rehm, Heidi, et al. Understanding the Genetics of Deafness. Harvard Medical School Center for Hereditary Deafness. Web. 26 October Smith, Richard JH and VanCamp, Guy. Deafness and Hereditary Hearing Loss. January 2007.University of Washington, Seattle. Web. 26 October University of Michigan Health System. “Gene Mutation That Causes Rare Form of Deafness Identified.” Science Daily 13 July Web. 26 October Yukon, Ronnee and Cummings, Michael. Human Genetics and Society. California: Cengage Learning,

Works Cited Photos, Diagrams and Artwork Slide 1: Photo: Family, meredithsmall.wordpress.com Slide 4: Diagram: Autosomal Recessive, U.S. National Library of Medicine. Slide 5: Diagram: Ear, Harvard Medical School Center for Hereditary Hearing Loss Slide 6: Diagram: Chromosome 13, National Library of Medicine, Genetics Home Reference: Genetics: GJB2 Slide 7: Artwork: Gap Junction Beta 2, University of Michigan Slide 9: Artwork: Genetic Testing, Concurring opinions. 12