title: Presymptomatic diagnosis of nonsyndromic hearing loss by genotyping.
abstract: BACKGROUND
  Nonsyndromic hearing loss (NSHL) is the most common type of hereditary hearing impairment (HHI). It is genetically heterogeneous, and although the exact number of genes is not known, 38 loci have been identified. By cloning the relevant genes and studying the function of the encoded proteins at the molecular level, it may be possible to impact the habitation of persons at risk for HHI. Currently, for select families, presymptomatic diagnosis of NSHL by genotyping is possible.
  
  
  OBJECTIVE
  To provide presymptomatic diagnosis of HHI to individuals in select families who have participated in linkage studies.
  
  
  METHODS
  In 2 large families with autosomal dominant HHI, genes for NSHL were mapped to chromosomes 6 (DFNA10) and 19 (DFNA4). In each family, the phenotype is one of progressive sensorineural hearing loss that begins in the individual's mid-30s and progresses to a severe-to-profound loss requiring amplification. Presymptomatic diagnosis was requested by, and provided to, 19 at-risk persons in these kindreds.
  
  
  RESULTS
  By reconstructing haplotypes through the use of short tandem repeat polymorphisms tightly linked to the disease gene, risk calculations and genetic counseling were provided to these persons.
  
  
  CONCLUSIONS
  By simple Mendelian genetics, the risk of inheriting a fully penetrant autosomal dominant NSHL gene from a single affected parent is 50% for each offspring. However, by reconstructing haplotypes in families in which an HHI gene has been localized, this risk can be changed substantially.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, University of Iowa, Iowa City 52242, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Chen
authors.forename: R F
authors.initials: RF
authors.lastname: Mueller
authors.forename: S D
authors.initials: SD
authors.lastname: Prasad
authors.forename: J H
authors.initials: JH
authors.lastname: Greinwald
authors.forename: J
authors.initials: J
authors.lastname: Manaligod
authors.forename: A C
authors.initials: AC
authors.lastname: Muilenburg
authors.forename: K
authors.initials: K
authors.lastname: Verhoeven
authors.forename: G
authors.initials: G
authors.lastname: Van Camp
authors.forename: R J
authors.initials: RJ
authors.lastname: Smith
mesh_terms: D002896:Chromosomes, Human, Pair 6; D005817:Genetic Counseling; D005820:Genetic Testing / Q000379:methods; D005838:Genotype; D006239:Haplotypes; D006319:Hearing Loss, Sensorineural / Q000175:diagnosis* / Q000235:genetics*; D006801:Humans; D010375:Pedigree; D011336:Probability