Linkage disequilibrium between IDUA kpnI-VNTR haplotype in Mexican patients with MPS-I

The MPS-I is an autosomal recessive disorder caused by mutations in the IDUA gene that induce to a deficiency of glycosidase alpha-L-iduronidase that is required for degradation of heparan and dermatan sulfate. This disorder expresses a wide range of clinical symptoms.

Kpnl (K) and VNTR (V) intragenic polymorphisms at the IDUA gene were studied in mestizo and Huichol Indian Mexican populations as well in 13 MPS-I patients. Data from Australian normal and MPS-I (2-4) individuals were also studied.

Genotypes for IDUA K and V sites in Mexicans were in agreement with Hardy-Weinberg expectations, except for site K in Huichols. Individually, allele frequency distributions were different (p < 0.05) in the two normal groups for the V site. K-V haplotype frequency distributions (HFDs) in these two normal groups were also different as compared with normal Australians. In Mexican MPS-I patients, HFD was different (p < 0.05) with respect to both Mexican normal groups, and non-different when compared with normal or MPS-I Australians. This can be taken as evidence of linkage disequilibrium between K-V polymorphism and MPS-I gene mutation(s) at the IDUA region. A similar finding was reported. However, disequilibrium in Mexicans was determined by haplotypes different from those in Australia. In Mexican MPS-I patients, haplotype K2-V1 is increased and K1-V3 decreased with respect to the Mexican mestizo (p < 0.05), while in Australians, MPS-I patients had an increase of haplotypes K2-V2 and K1-V2 with respect to expected frequency.

The similar HFD between Mexican and Australian MPS-I patients suggests a common genetic origin, that MPS-I mutations were introduced to Mexico by Spaniards, and that such mutations predate the dispersion between Mexican and Australian Caucasian ancestors. The differences in disequilibrium are explained rather by genetic drift.