Jeffrey O'Riordan

Influence of LRP5 polymorphisms on normal variation in BMD

Genetic studies based on cohorts with rare and extreme bone phenotypes have shown that the LRP5 gene is an important genetic modulator of BMD. Using family‐based and case‐control approaches, this study examines the role of the LRP5 gene in determining normal population variation of BMD and describes significant association and suggestive linkage between LRP5 gene polymorphisms and BMD in >900 individuals with a broad range of BMD.

The gene for X-linked hypophosphataemic rickets maps to a 200-300 kb region in Xp22.1, and is located on a single YAC containing a putative vitamin D response element (VDRE)

The location of the HYP gene, which determines X-linked hypophosphataemic rickets, has been refined considerably by linkage analysis, and three new microsatellite primers isolated, Cap32 (DXS7473), Cap29 (DXS7474) and 7v2 (DXS7475). The locations of four other markers have also been determined (DXS1226, AFMa176zb1, AFMa152wc5, and AFM346azc1). Markers Cap29 and Cap32 are the closest distal markers to the gene with zetamax=11.93, thetamax= 0.018 and zetamax=12.03, thetamax = 0.015 respectively. Both Cap29 and Cap32 are proximal to DXS365 and AFMa176zb1, as deduced by screening non-chimaeric yeast artificial chromosomes (YACs) from a contig spanning the HYP gene. A single crossover places AFMa176zbl distal to the disease gene. There are no recombinations between 7v2 and HYP (zetamax=12.9, thetamax=0.0), or between 7v2 and adjacent markers Cap32, Cap29, AFMa176zb1, DXS1683 and DXS365. However screening of YAC clones encompassing the HYP gene and also P1 clones localises 7v2 distal to Cap29 and Cap32, and proximal to DXS443. Marker DXS1226 is placed outside the region containing the gene, and is located proximal to DXS274 as confirmed by a crossover for this marker and DXS41 against HYP and its presence on YAC 83B05. Genetic mapping of CEPH pedigrees, and screening of YACs places AFMa152wc5 and AFMa346zcl between DXS1683 and DXS1052. The following gene marker map presents the best order for the HYP region: Xptel-DXS43-DXS999-DXS443-(DXS365/DXS74 75/AFMa176zb1)-(DXS7474/DXS7473)-HYP- DXS1683-(AFMa152wc5/AFMa346zc1)-DXS1052-DXS 274 -(DXS41/DXS1226)-Xcen. The distance between the cluster of distal flanking markers Cap29 (DXS7474), Cap32 (DXS7473), and DXS1683 is approximately 300 kb, as deduced from physical map data from a YAC contig spanning the gene. Thus the gene for HYP is contained within a single YAC (900AO472). Of further interest, is the location of a putative vitamin D response element (VDRE) on this YAC.

Three DNA markers for hypophosphataemic rickets

SummaryThis paper presents three markers, 16D/E, pHMAI (DXS208), and CRI-L1391 (DXS274), that show close linkage for X-linked hypophosphataemic rickets (HYP). DXS274 is closely linked to HYP (θmax= 0.00, Zmax = 4.20), and DXS41 (99.6), (θmax= 0.00, Zmax = 5.20). Marker 16D/E maps distal to the disease locus (θmax= 0.05, Zmax = 3.11). The pHMAI probe recognises the same restriction fragment length polymorphism (RFLP) as 99.6. Multipoint analysis suggests that the most probable order of loci is Xpter-(DXS43, 16D/E)-HYP-DXS274-(DXS208, DXS41)-Xcen. The location of DXS274 distal to HYP cannot be excluded, as no recombinants were observed between DXS274 and HYP, or between DXS274 and DXS41/DXS208. One of the families contains a large number of recombinants, four of which are double recombinants. This most probably means that the disease in this family maps elsewhere on the X chromosome or on an autosome, indicating locus heterogeneity.

Refining the genetic map for the region flanking the X-linked hypophosphataemic rickets locus (Xp22.1-22.2)

We have screened fourteen kindreds with X-linked hypophosphataemic rickets with four microsatellite markers, viz. AFM163yh2, DXS999 (AFM234yf12), DXS443 and DXS365, in order to refine the genetic map flanking the gene, and to define a close flanking interval for the construction of a yeast artificial chromosome (YAC) and cosmid contig. The genetic data were enhanced after the isolation of a large 1.2-megabase YAC derived from AFM163yh2, in which marker DXS274 was present but not DXS365 or DXS443. Against HYP, DXS365, AFM163yh2 and DXS443 showed no recombinants (Zmax = 18.1, Zmax = 9.9, and Zmax = 16.0 respectively). DXS999 gave Zmax = 9.6 at 4% recombination and lies distal to HYP but proximal to DXS197 and DXS43. The disease gene and markers AFM163yh2 and DXS365 are flanked by DXS443 and DXS274. Combining the genetic and physical data, we are able to propose the following gene marker order: Xptel-DXS43-DXS197-DXS999-DXS443-[(DXS365-AFM163yh2), HYP]-DXS274-DXS41-Xcen.

New markers for linkage analysis of X-linked hypophosphataemic rickets.

Three polymorphic markers have been used to improve the genetic map of the region Xp22.1-p22.2, which contains the HYP (hypophosphataemic rickets) locus. DXS365 gave no recombinants with HYP, with a peak Lod score of 5.4 at θ = 0.0. A microsatellite marker mPA274 was derived for the DXS274 locus; it detects five alleles with a polymorphism information content of 0.55. Combining information from this microsatellite and the original DXS274 marker, probe CRI-L1391, the peak Lod score for DXS274 against HYP was 9.6 at θ = 0.02. A microsatellite associated with the DXS207 locus (mPA207) gave a peak lod score against HYP of 4.7 at θ = 0.14. A consideration of key recombinants and multilocus analysis suggests the gene order: Xpter-DXS207-DXS43-DXS197-(DXS365, HYP)-DXS274-DXS41-Xcen.