The Construction of a Yeast Artificial Chromosome (YAC) Contig in the Vicinity of the Usher Syndrome Type IIa (USH2A) Gene in 1q41

The gene for Usher syndrome type II (USH2A), an autosomal recessive syndromic deafness, has been mapped to a region of 1q41 flanked proximally by D1S217 and distally by D1S439. Using sequence-tagged sites (STSs) within the region, a total of 21 yeast artificial chromosome (YAC) clones were isolated and ordered into a single contig that spans approximately 11.0 Mb. The order of microsatellite and STS markers in this region was established as D1S505–D1S425–DXS217–D1S556–D1S237–D1S474–EB1–EB2–KB6–AFM144XF2–KB1–KB4–D1S229–D1S490–D1S227–TGFβ2–D1S439. Analysis of newly positioned polymorphic markers in recombinant individuals in two Usher syndrome type IIa families has enabled us to identify DXS474 and AFM144XF2 as two flanking markers for the Usher type IIa locus. The physical distance between the two markers is 1.0 Mb. This region is covered by eight YACs from the CEPH library: 945f7, 867g9, 762a6, 919h3, 794b8, 785h4, 848b9, and 841g2. A long-range physical map of the Usher type IIa critical region, usingMluI,BssHII,NotI,EagI, andSacII, has been developed.