Phenotype-genotype correlations in otosclerosis: clinical features of OTSC2.

As part of the GENDEAF consortium, a European multi-centre otosclerotic database is under construction to collect the clinical data of as many otosclerotic patients as possible. Otosclerosis represents a heterogeneous group of heritable diseases in which different genes may be involved regulating the bone homeostasis of the otic capsule. The purpose of the GENDEAF otosclerosis database is to explore the otosclerotic phenotype more in depth. Subtle phenotypic differences otherwise not visible, may become statistically relevant in a large number of patients. Their identification can lead towards the discovery of new genes involved in the pathway of abnormal bone metabolism in the human labyrinth. As soon as one of the otosclerotic genes is identified, it would allow us to identify genotype-phenotype correlations. From other deafness genes, it is know that different mutations in the same gene may cause similar phenotypes of varying severity. Also the variability in treatment outcomes after surgery or fluoride therapy may result not only from differences in practice or surgical skill among physicians, but also on the nature of the underlying disorder. Screening large numbers of patients would make it possible to undertake clinical trials comparing different treatments. Identifying a genetic susceptibility would allow us to dissect out possible environmental factors that prevent the expression of clinical otosclerosis in those that carry the mutated gene and yet retain normal hearing.