Title: Genetics and Hearing Loss: Clinical and Molecular Characteristics

Transcription

1 Session # : 46 Day/Time: Friday, May 1, 2015, 1:00 4:00 pm Title: Genetics and Hearing Loss: Clinical and Molecular Characteristics Presenter: Kathleen S. Arnos, PhD, Gallaudet University This presentation will provide an overview of the clinical characteristics and molecular mechanisms of hereditary hearing loss in infants, children and adults. Case studies will illustrate modes of inheritance (both monogenic and complex inheritance patterns) and common nonsyndromic and syndromic forms of genetic hearing loss. Participants will learn basics of pedigree construction and the importance of pedigree analysis as a tool to understand and evaluate genetic risk factors. Recent advances in molecular genetics which have an increasing impact on the diagnostic evaluation of deaf and hard-of-hearing children and adults will be presented. This includes information on testing strategies ranging from DNA sequencing to identify mutations in single genes to whole exome and whole genome sequencing approaches. Information about recent research investigating genetic factors which contribute to age-related and noise-induced hearing loss will also be discussed. A major goal of the presentation will be to provide strategies for speech and hearing professionals to make appropriate referrals for genetic evaluation, testing and counseling and provide meaningful follow-up with families with hereditary hearing loss. Overview of learning outcomes: After completion of this program you will be able to describe the difference between monogenic and complex inheritance and the relative contributions of these modes of inheritance to congenital, early-onset, or late-onset hearing loss. list two differences between syndromic and non-syndromic hearing loss and specify the relative proportion of each in genetic hearing loss. name one monogenic inheritance pattern that is common in genetic forms of congenital and early-onset hearing loss. make appropriate referrals for genetic evaluation and counseling of individuals with hearing loss, including explaining clinical procedures and basic information about current genetic testing methods. 1 P age

2 Topic Outline: 1. Genetics in Context: The Case History of Sonya Clinical History Evaluation Strategy Family and Medical History, Genetic Evaluation and Testing When and Why to Refer? The Role of the Audiologist 2. Overview of Epidemiology of Hearing Loss Epidemiologic Studies Age at Onset: Pediatric vs. Adult Inheritance: Monogenic vs. Complex Inheritance Syndromic vs. Non-syndromic 3. Overview of DNA Structure Normal DNA and Chromosome Structure Types of Mutations SNPs in Health and Disease 4. Pedigree Construction and Analysis for Health Care Professionals In the age of genomics, why pedigrees? Standard pedigree information and symbols (see page 3) Basic pedigree construction for Toby, a 3-month-old child with hearing loss (use page 4) 5. Review of Mongenic Inheritance Patterns Mendelian: Autosomal and Sex-Linked and Relative Frequency in Hearing Loss genotype vs. phenotype Hearing loss is one of the most genetically heterogeneous traits known in humans basic terminology of transmission genetics: allele, locus, homozygous, heterozygous, homologs, mutant vs. wild-type alleles Autosomal dominant inheritance: penetrance and expressivity Autosomal recessive inheritance: consanguinity and assortative mating The Y-linked gene for hearing loss that turned out not to be. Mitochondrial (matrilineal) inheritance (topic outline continues on page 8) 2 P age

3 Table 1. Standard Pedigree Symbols Male P P Pregnancy b wk 30 y Female Marriage/mating 4 mo Sex unspecified Divorce 4 2 Number of individuals of sex indicated Consanguineous mating Affected individual Affected individual with 2 conditions or traits Monozygotic twins Proband Dizygotic twins d. 35 y SB Deceased individual I 1 2 Stillbirth II Spontaneous Termination of pregnancy Adoption Numbering of individuals in pedigree Proband is II 2 No offspring Infertility 3 P age

4

5 Table 2. A list of pedigree clues for autosomal dominant, x-linked recessive, mitochondrial, autosomal recessive, x-linked dominant, and chromosomal traits. (Adapted from LaraSig Health Professional Student Training Autosomal Dominant Affected fathers can have affected sons or daughters Affected mothers can have affected sons or daughters Condition appears in multiple successive generations Males and females are both affected, usually in equal proportions Unaffected individuals do not have affected children (Exceptions occur due to de novo mutations, variable expressivity, reduced penetrance or sex-limited expression) Autosomal Recessive Unaffected parents have affected children Condition usually appears in a single group of siblings Males and females are both affected, usually in equal proportions Conditions are more common when there is consanguinity X-Linked Recessive Males are exclusively or much more commonly affected than females Affected males are related to each other through unaffected females (carriers) Children of affected fathers are all unaffected Unaffected fathers do not transmit the condition to any of their descendants Mitochondrial Males and females are both affected, usually in equal proportions Only females transmit the condition to their children Affected individuals are related to each other through females Condition appears in multiple generations Chromosomal Best identified by cytogenetic testing when any of the following clinical findings are present: o Combinations of major and/or minor congenital anomalies o Mental retardation with or without major/minor anomalies o Recurrent pregnancy loss o Sexual development disorders o Infertility o Stillbirth or infant death 5 P age

6 6 P age Figure 2. Sample Pedigrees

7 7 P age

8 Topic Outline (Continued) 6. Mapping and Cloning of Genes for Hearing Loss Syndromic vs. non-syndromic loci Genes and auditory function o ion transport o structural integrity of the cochlea o transcription factors What might genetic testing tell us about Sonya? 7. Genetic Evaluation Testing Strategies in the Genomics Era American College of Medical Genetics and Genomics Evaluation Guideline for Clinical Evaluation and Etiologic Diagnosis of Hearing Loss Current Methodologies/Testing Platforms o Sanger Sequencing Still the Gold Standard o Microarrays o Next Generation Sequencing/Massively Parallel Sequencing What can we Expect in the Next Several Years? Considerations for Selection of Testing Platform 8. Introduction to Complex Inheritance Basic Concepts and the Threshold Model Genetic Factors in Age Related Hearing Impairment (ARHI) and Noise Induced Hearing Loss Overview of Recent Studies and Future Directions 9. Additional Case Studies (as time permits) 10. Future Directions 8 P age

9 Resources for Parents Genetics Home Reference, U.S. National Library of Medicine American College of Medical Genetics brochure: Hearing Loss, Genetics and Your Child Available free of charge in English and Spanish from the National Coordinating Center for the Regional Genetic and Newborn Screening Services Collaboratives (NCC) Schwartz, S. (editor). Choices in Deafness. 3rd edition. Woodbine House, (This book includes a chapter on genetics written for parents.) Resources for Audiologists/Health Care Professionals Genetics Testing Registry, National Library of Medicine Gene Tests/Gene Clinics, University of Washington Selected References Alford RL, Arnos KS, Fox M, Lin JW, Palmer CG, Pandya A, Rehm HL, Robin NH, Scott DA, Yoshinaga-Itano C. ACMG Working Group on Update of Genetics Evaluation Guidelines for the Etiologic Diagnosis of Congenital Hearing Loss; Professional Practice and Guidelines Committee. American College of Medical Genetics and Genomics guideline for the clinical evaluation and etiologic diagnosis of hearing loss. Genet Med Apr; 16(4): Angeli S1, Lin X, Liu XZ. Genetics of hearing and deafness. Anat Rec (Hoboken) Nov; 295(11): Kohrman DC, Raphael Y. Gene therapy for deafness. Gene Ther Dec; 20(12): Shearer AE1, Smith RJ. Genetics: advances in genetic testing for deafness. Curr Opin Pediatr Dec; 24(6): Sliwinska-Kowalska M1, Pawelczyk M. Contribution of genetic factors to noise-induced hearing loss: a human studies review. Mutat Res Jan-Mar; 752(1):61-5. Ushakov K, Rudnicki A, Avraham KB.MicroRNAs in sensorineural diseases of the ear. Front Mol Neurosci Dec 23; 6:52. Yan D1, Tekin M, Blanton SH, Liu XZ. Next-generation sequencing in genetic hearing loss. Genet Test Mol Biomarkers Aug;17(8): P age