Three polymorphic markers have been used to improve the genetic map of
the region Xp22.1-p22.2, which contains the HYP (hypophosphataemic ri
ckets) locus. DXS365 gave no recombinants with HYP, with a peak Lod sc
ore of 5.4 at theta = 0.0. A microsatellite marker mPA274, was derived
for the DXS274 locus; it detects five alleles with a polymorphism inf
ormation content of 0.55. Combining information from this microsatelli
te and the original DXS274 marker, probe CRI-L1391, the peak Lod score
for DXS274 against HYP was 9.6 at theta = 0.02. A microsatellite asso
ciated with the DXS207 locus (mPA207) gave a peak lod score against HY
P of 4.7 at theta = 0.14. A consideration of key recombinants and mult
ilocus analysis suggests the gene order: Xpter-DXS207-DXS43-DXS197-(DX
S365, HYP)-DXS274-DXS41-Xcen.