D1S2721), the Stanford G3 radiation hybrid (RH) panel (Research Genetics) was used to estimate the distances between these markers and the GBA gene. Following Cox et al.(1990) and Moisio et al.(1996), a 1 cR/50 kb ratio was used to calculate the distance in centimorgans (900 kb/1 cM), which we transformed into v values using the Haldane map function. Hybrid DNA was amplified by PCR using standard protocols. Primers used to detect the presence of the GBA gene were as follows: forward, 5-AACCATGATTCCCTATCTTC-3; reverse, 5-GAGGCACATCCTTAGAGGAG-3. As noted by Moisio et al.(1996), RH mapping generally yields greater distances between marker loci than does meiotic mapping.

Previously, we reported a common disease haplotype in Spanish patients with GD bearing the N370S mutation (Cormand et al. 1998). Analyses of 66 Ashkenazi Jewish patients and five additional Spanish patients with GD, using six microsatellite markers, revealed that most of the Jewish and Spanish N370S chromosomes share alleles for five of these markers. Figure 1a shows the haplotype of the 73 Ashkenazi Jewish N370S chromosomes, of the 104 analyzed, for which the phase had been established for all the markers (phases were determined by use of samples from parents and/or siblings). Forty-three (59%) have a conserved haplotype for mark-