Linkage of tuberculosis to chromosome 2q35 loci, including NRAMP1, in a large aboriginal Canadian family.

An epidemic of tuberculosis occurred in a community of Aboriginal Canadians during the period 1987-89. Genetic and epidemiologic data were collected on an extended family from this community, and the evidence for linkage to NRAMP1, a candidate gene for susceptibility to mycobacterial diseases, was assessed. Individuals were grouped into risk (liability) classes based on vaccination, age, previous disease, and tuberculin skin-test results. Under the assumption of a dominant mode of inheritance and a relative risk of 10, which is associated with the high-risk genotypes, a maximum LOD score of 3.81 was observed for linkage between a tuberculosis-susceptibility locus and D2S424, which is located just distal to NRAMP1, in chromosome region 2q35. Significant linkage was also observed between a tuberculosis-susceptibility locus and a haplotype of 10 NRAMP1 intragenic variants. No linkage to the major histocompatibility-complex region on chromosome 6p was observed, despite distortion of transmission from one member of the oldest couple to their affected offspring. The ability to assign individuals to risk classes was crucial to the success of this study.