Gaucher disease (GD), caused by a deficiency of the lysosomal enzyme glucocerebrosidase (GBA), is the most common human glycolipid storage disease. The incidence of the disease is particularly high in the Ashkenazi Jewish population, with a carrier frequency of 0.068. The 1226A-->G and 84GG mutations are the two predominant disease-causing alleles. We investigated the association of various mutations in the GBA gene with different alleles of a highly polymorphic site in the adjacent pyruvate kinase (PKLR) gene. Ninety-seven unrelated type I GD patients of various genotypes were studied to determine their genotype for the PKLR gene trinucleotide repeat polymorphism. One hundred out of 104 (96%) alleles carrying the 1226G mutation also carried the A1 allele of the PKLR gene, which is present in only 6.7% of the control population. The calculated linkage disequilibrium between 1226G and the A1 allele of the PKLR gene is 0.957. Mutation 84GG was found to be uniquely associated with the PKLR A6 allele, with a linkage disequilibrium of 1.00. The association of several less frequent GD mutations with PKLR alleles was also studied. These results support the hypothesis that the 1226G and 84GG mutations in the Ashkenazi Jewish population each originated in a single founder. Further studies of the association of the 1226G and 84GG mutations with PKLR alleles in European non-Jewish GD patients could help in the study of the chronological order of these mutations and may shed light on the history of the Ashkenazi Jews in the past two millennia.