Usher syndrome represents the association of a hearing impairment with retinitis pigmentosa and is the most frequent cause of deaf-blindness in humans. It is inherited as an autosomal recessive trait which is clinically and genetically heterogeneous. Some patients show abnormal organization of microtubules in the axoneme of their photoreceptors cells (connecting cilium), nasal ciliar cells and sperm cells, as well as widespread degeneration of the organ of Corti. Usher syndrome type 1 (USH1) is characterized by a profound congenital sensorineural hearing loss, constant vestibular dysfunction and prepubertal onset of retinitis pigmentosa. Of three different genes responsible for USH1. USH1B maps to 11q13.5 (ref. 10) and accounts for about 75% of USH1 patients. The mouse deafness shaker-1 (sh1) mutation has been localized to the homologous murine region. Taking into account the cytoskeletal abnormalities in USH patients, the identification of a gene encoding an unconventional myosin as a candidate for shaker-1 (ref. 14) led us to consider the human homologue as a good candidate for the gene that is defective in USH1B. Here we present evidence that a gene encoding myosin VIIA is responsible for USH1B. Two different premature stop codons, a six-base-pair deletion and two different missense mutations were detected in five unrelated families. In one of these families, the mutations were identified in both alleles. These mutations, which are located at the amino-terminal end of the motor domain of the protein, are likely to result in the absence of a functional protein. Thus USH1B appears as a primary cytoskeletal protein defect. These results implicate the genes encoding other unconventional myosins and their interacting proteins as candidates for other genetic forms of Usher syndrome.

In a male patient with a 45,X karyotype, the terminal part of the Y chromosome short arm was translocated as a single block on to the X chromosome. This rearranged X chromosome was, in every regard, the same as that present in XX males resulting from an abnormal X-Y interchange. Correlations between the phenotype of this patient and the extent of the deletions on the X and Y chromosomes allowed us to map the genes responsible for most features of the Turner syndrome between DXS432 and Xqter on the X chromosome, and the homologous Y genes either on Yp in interval 4 or on Yq. The molecular analysis of this X-Y translocation allowed us also to reduce the interval for the X-linked recessive chondrodysplasia punctata gene to a 1.5 Mb interval between DXS432 and DXS31.

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