Closing in on the BPES gene on 3q23: mapping of a de Novo reciprocal translocation t(3;4)(q23;p15.2) breakpoint within a 45-kb cosmid and mapping of three candidate genes, RBP1, RBP2, and beta'-COP, distal to the breakpoint.

BPES is a genetic disorder presenting with blepharophimosis, ptosis of the eyelids, epicanthus inversus, and telecanthus. BPES type I is associated with female infertility, whereas type II presents without additional symptoms. Hitherto, it remains unknown whether BPES type I results from a defect in a single gene or from a contiguous gene syndrome. Previous cytogenetic and linkage analyses have assigned a BPES locus to 3q23, in a 5-cM interval between D3S1615 and D3S1316. In this report, we describe the molecular and physical characterization of the 3q23 breakpoint in a BPES patient with a t(3;4)(q23;p15.2) translocation. Eight YACs located around and within the D3S1615-D3S1316 interval were mapped relative to the 3q23 breakpoint; 5 YACs spanning the 3q23 breakpoint were identified. Thirteen STSs and ESTs were localized on the YAC map. Subsequent hybridization of 2 YACs spanning the breakpoint to the Human RPCI1 PAC Library and the Human Chromosome 3 LLNL Cosmid Library resulted in the identification of 12 PACs and 50 cosmids respectively, allowing the construction of a detailed PAC and cosmid physical map. A refined position-telomeric to the breakpoint-of 3 candidate genes, cellular retinol-binding proteins 1 and 2 (RBP1, RBP2) and the coatomer beta' subunit (beta'-COP), was obtained on this physical map. Furthermore, a PAC and cosmid contig encompassing the breakpoint was constructed. PAC 169-C 10 and cosmid 11-L 10 crossing the breakpoint have sizes of 110 and 45 kb, respectively. The isolation of coding sequences in these clones and in the rest of the contig will greatly facilitate further efforts toward positional cloning of the gene(s) involved in BPES.