DXS165 detects a translocation breakpoint in a woman with choroideremia and a de novo X; 13 translocation

Abstract

The search for the gene for choroideremia (MIM 30310), a rare retinal dystrophy, has been of great interest due to the existence of several choroideremia patients with well-defined structural chromosome aberrations, thus providing the basis for a reverse genetics approach to the isolation of this disease gene. This report details our molecular studies of a woman with choroideremia and a de novo X; 13 translocation. Pulsed-field gel electrophoresis using a contour-clamped homogeneous electric field apparatus has allowed detection of the translocation breakpoint with the anonymous DNA marker p1bD5 (DXS165) and the mapping of this probe to within 120 kb of the breakpoint. In addition, we have used this probe to isolate a clone (pCH4) from a 100-kb jumping library which has crossed a rare-cutting restriction site (XhoI) between DXS165 and the choroideremia gene and detects the translocation breakpoint using this enzyme. Although DXS165 lies within 120 kb of the breakpoint and Cremers et al. (1987, Clin. Genet. 32: 421-423; 1989, PNAS 86: 7510-7514) have detected deletions of DXS165 in 3 of 30 choroideremia probands, we have detected no deletions of this marker or of pCH4 in 42 unrelated probands with this retinal disease.

Isolation of a candidate gene for choroideremia.

“…A similar approach to choroideremia was feasible because the locus for choroideremia has been mapped to Xq2l.1-Xq2l.2 by tight linkage to polymorphic DNA markers (11)(12)(13)(14)(15)(16), by the study of individuals with choroideremia who have large deletions of this region (17)(18)(19)(20)(21)(22)(23), and by the characterization oftwo women with choroideremia and de novo X;autosomal translocations (24)(25)(26). Recently, Cremers et al (27) isolated a candidate cDNA for the choroideremia gene that was disrupted in males with the disease by large [>40-kilobase (kb)] genomic deletions and in a female with the disease by an X;13 translocation.…”

“…By chromosome walking, from nearby probes, we have isolated genomic sequences from the translocation breakpoint in a female with choroideremia and an X;13 translocation (26) and used them to identify a candidate choroideremia cDNA.$ This gene is very similar but not identical to that reported by Cremers et al (27). Expression studies in 34 unrelated probands with isolated choroideremia indicate that, while the genomic structure of this region is unaltered in all these patients, mRNA levels for this gene in 25 of these patients are markedly reduced or absent compared to normal controls.…”

Choroideremia: linkage analysis with physically mapped close DNA-markers

“…The summary of the order and orientation of these loci as established by physical mapping is Xcen-DXS367-DXS233-DXS165-pZll-DXS95-DXYS1-DXYS69-Xtel (Cremers et al 1989a(Cremers et al , 1989bMerry et al 1989Merry et al , 1990D.Page, personal communication).…”

“…The order of marker loci: DXS367-pZ11-DXS95-DXYS69, was assumed based on physical mapping data (Cremers et al 1989a(Cremers et al , 1989bMerry et al 1989Merry et al , 1990D.Page, personal communication). The marker loci were estimated to span a genetic distance of 2.5 cM, where the genetic distances between the marker loci were i cM for DXS367-pZll and pZll-DXS95, and 0.5 cM for DXS95-DXYS69.…”

Live Birth of a Healthy Boy after Preimplantation Genetic Testing for X-Linked Choroideremia Disorder

“…Alignment and variant calling were performed using NextGENe software (SoftGenetics). Sanger sequencing was performed in order to confirm any detected variant [13][14][15][16][17][18][19][20][21][22][23][24][25].…”