Hearing impairment is the most frequent sensory deficit in humans and affects one newborn out of 500. The prevalence rises to 3,5/1000 in teenagers due to retarded forms. Most of hearing impairments (about two thirds) have a genetic origin, with recessive, dominant or X-linked mode of inheritance. Some rare forms can be linked to mitochondrial DNA. Molecular diagnosis (i.e. defining the molecular basis of the disease, genes and precise DNA variants) is essential for the follow-up of patients and families.

The project intends to perform exome sequencing on 30 samples of families presenting with hearing impairment. Families have been included based on the genetic origin of the hearing impairment (familial cases) and the exclusion of the involvement of 74 known deafness genes. Exome sequencing (sequencing of the coding regions of all known genes, about 22,000) in these cases may underly new gene/disease relationships.

Exome sequencing will be performed of 10 trios that each include two affected and one non affected members of a family. Filtering of variants will be performed based on frequency. For each trio, data will be analysed in parallel to follow segregation of the variant(s) in candidate genes. The selected candidate genes will be further characterized in order to ascertain their involvement in hearing function.

Finally, once these new genes are well defined as "deafness genes" , their screening will be added to existing diagnostic panels.

Inclusion Criteria:

• Families presenting with familial hearing impairment, underlying the genetic basis, for whom 74 deafness genes have already been excluded (no evidence of pathogenic genotype)

Exclusion criteria:

- sporadic cases of hearing impairment, or resolved familial cases

Hearing impaired patients and relatives