Third Joubert Syndrome Locus on Chromosome 6 mapped by European Group

A first locus for Joubert syndrome was mapped in 1999 by a German group in collaboration with colleagues from Middle East, based on a technique called homozygozity mapping in few consanguineous Arab families. Up to now, the gene has not yet been exactly identified.

In 2003 a second locus on chromosome 11 was independently found by two groups, one headed by Dr. Joseph Gleeson, again based on consanguineous families from the Middle East, the other from an Italian group investigating a consanguineous family from Sicily. The clinical phenotype described varies considerably between these families, affected individuals in the Italian family developed renal insufficiency in their late teen-age, but have no evidence of retinal involvement, however, the patients from Middle East have various ophthalmological findings.

A third locus on chromosome 6 has now been identified as a joint effort by the genetic laboratory of Michel Koenig, Strasbourg, France, using DNA from a large consanguineous Turkish family living in Norway (supplied by Dr. Brejvik) and a consanguineous Swiss family provided by Eugen Boltshauser. In these patients, all older than 17 years, there is variable retinal involvement and cognitive impairment, but no evidence of renal insufficiency. It seems remarkable that all 3 loci have been identified in families with consanguinity. The majority of other families with affected children do not link to the known loci or are too small. There are certainly more chromosome locations to be identified. (The results of this new locus will soon be published in Journal of Medical Genetics.)

Eugen Boltshauser

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