Objectives Role of Medical Genetics in Hearing Loss Evaluation. 5 y.o. boy with severe SNHL

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1 Objectives Role of Medical Genetics in Hearing Loss Evaluation Millan Patel, MD UBC Dept. of Medical Genetics October 22, 2010 Case presentation to illustrate importance of defining syndromic hearing loss Genetic contributions to hearing loss Types of inheritance Why is Medical Genetics consultation important? Future of genetic testing 5 y.o. boy with severe SNHL 1

2 Syndromic hearing loss Syndromic associated with malformations of the external ear or other organs or with medical problems involving other organ systems Over 400 genetic syndromes described to include hearing loss Inheritance pattern in family can be helpful Inheritance Patterns Autosomal dominant inheritance Pedigree Boxes = males. Circles = females. Diamond = unspecified gender. Shading = affected. Double line = consanguinity P Disorder appears in several generations of a family. Affected males = females Affected parents have a 50% risk of an affected child with each pregnancy. Waardenburg syndrome Autosomal dominant syndromic hearing loss Most common: Waardenburg syndrome 2 nd most common: BOR syndrome abnormal pinnae, ear pits, Mondini dysplasia, branchial clefts or cysts, kidney abnormalities Stickler: cleft palate (Pierre Robin sequence), severe myopia, early arthritis NF2: treatable 2

3 Autosomal recessive inheritance Disorders often appear in only one generation of a family. Carrier couples have a 25% risk of an affected child with each pregnancy. Autosomal recessive syndromic hearing loss Pendred syndrome congenital SNHL, Mondini dysplasia or dilated vestibular aqueduct, abnormal vestibular function, goiter in puberty or adulthood Jervell and Lange-Nielsen syndrome congenital deafness and long QTc (arrhythmia, sudden death) Treatable: Biotinidase deficiency episodic or progressive ataxia and progressive SNHL, with or without neurologic or cutaneous symptoms Refsum disease severe progressive SNHL and retinitis pigmentosa X-linked inheritance Maternal Inheritance X-linked dominant disorders are few in number. Inheritance through the maternal lineage. Sperm do not contribute mitochondria to the embryo. Male to male transmission is never seen. Carrier females may show mild to moderate symptoms of certain X-linked disorders. X-linked syndromic hearing loss Alport syndrome progressive SNHL, glomerulonephritis, variable eye findings Adrenoleukodystrophy ADD, declining school performance, failed hearing test Mitochondrial pedigree features can be short stature, diabetes, HL aminoglycoside-induced hearing loss is more likely in people with A1555G change 60% of people with type II diabetes and A3423G change have hearing loss Benefits of Medical Genetics consultation Separate syndromic from non-syndromic hearing loss Identify pattern of inheritance so relatives at risk can be offered screening Medical Genetics clinics available in: Victoria, Vancouver, Kelowna, Prince George Questions? Call and ask to speak to a Genetic Counsellor 3

4 Gene tests available in BC Sequencing of Connexin 26 = GJB2 Deletion of Connexin 30 = GJB6 (15-20% CMV) (15-25% Connexin 26/30) (DFNA1-50) (DFNX1-2) (DFNB2-77) Testing relatives at risk Children at risk for hereditary hearing loss should undergo screening audiometry and, if the family-specific gene change(s) are known, molecular genetic testing. Future Testing Gene testing Targeted gene testing chips Array CGH Rule in vs. rule out NextGen Sequencing Exome Genome Direct to consumer testing 4

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6 Gene Chips Soundgene.com blood spot sample; $198 Connexin 26/GJB2: 4 most common of 678 DNA letters are tested Connexin 30/GJB6: testing for the large deletion (missing 309,000 DNA letters) 6 mitochondrial changes tested Pendred/SLC26A4: 4 most common of 2340 DNA letters are tested Look for CMV DNA Sensitivity: 34% (JAMA, 2010) Array CGH = Fancy karyotype Chromosomes: resolution of 7 million DNA letters Array CGH: resolution of 200,000 DNA letters NextGen Sequencing Exome sequencing ($7500) Determine the 30 million DNA letters that encode proteins Genome sequencing ($24,000) Determine all 6 billion DNA letters in a cell Direct to consumer testing Poll Pros: faster test development, empowers consumers to learn, most health care providers have some difficulty interpreting genetic testing Cons: Possibility for harm/nasty surprises without pre- and post-test counselling, biased information, unnecessary health care usage; lack of regulation at present. Regularly updated information on genetics of hearing loss: search Hearing loss 5