Nijmegen - Researchers from the Netherlands have discovered genetic defect that leads to disruption of the hair cells in the inner ear, which convert acoustic stimuli into nerve signals. According to the report in the Journal of Medical Genetics (2002;), the genetic defect was initially discovered in 12 families. Later analyzes showed that the genetic defect is probably widespread in Europe.
Inner ear hearing loss often has genetic causes. So far, disorders have been found in 118 genes that hinder or prevent the transmission of acoustic signals in the inner ear. Most genetic defects result in deafness in childhood. In the families examined by team led by Hannie Kremer from the Radboud Universitair Medisch Centrum in Nijmegen, inner ear hearing loss did not appear on average until they were 30 years old. Hearing disorders at this age are also to large extent genetic. Heritability is estimated at 30 to 70%. However, genetic causes have so far rarely been found.
The researchers tracked down the new genetic defect through an exome analysis of diseased members of family. A short section (deletion) was missing from the RIPOR2 gene on chromosome 6. The genetic defect was present in 20 of the 23 family members with confirmed hearing loss. However, it was also found in three other family members aged 23, 40 and 51 who did not yet have any hearing impairment.
This prompted the researchers to add inner ear hearing loss in further 11 families with an increased incidence of inner ear hearing loss after the genetic defect search. To their surprise, the identical genetic variant was found in 39 of 40 family members with confirmed hearing loss as well as in two people aged 49 and 50 who were not (yet?) Affected by hearing loss.
An identical genetic defect in unrelated persons indicates that it is an "older" mutation. The researchers first researched the "SE-NL" database, which has stored the genetic data of 22,952 people from the southwest of the Netherlands. There were 18 hits, which results in prevalence of 0.0392% in the local population.
The "gnomAD" database with 32,287 people (non-Finnish) of north-western European origin was then analyzed. There people or 0.0077% had the deletion on chromosome 6.
Extrapolated to the population, the genetic defect could explain the inner ear hearing loss of more than 13,000 people in the Netherlands and of another 30,000 people in northwestern Europe. It can be assumed that the deletion, the origin of which apparently goes back long way in evolution, is also widespread in other regions of Europe and in Germany.
Experiments on mice showed that the genetic defect leads to disorder in the hair cells. There, the movements induced by the sound waves in the membranes of the organ of Corti are converted into nerve impulses.