Background: A Guam variant of amyotrophic lateral sclerosis (ALS-G) and parkinsonism dementia complex (PDC-G) are found in the Chamorro people of Guam. Both disorders have overlapping neuropathologic findings, with neurofibrillary tangles in spinal cord and brain. The cause of ALS-G-PDC-G is unknown, although inheritance and environment appear important. Because neurofibrillary tangles containing tau protein are present in ALS-G-PDC-G, and because mutations in the tau gene (TAU) cause autosomal dominant frontotemporal dementia, TAU was examined as a candidate gene for ALS-G-PDC-G.
Methods: TAU was evaluated by DNA sequence analysis in subjects with ALS-G-PDC-G, by linkage analysis of TAU polymorphisms in an extended pedigree from the village of Umatac, and by evaluation of linkage disequilibrium with polymorphic markers flanking and within TAU.
Results: Linkage disequilibrium between ALS-G-PDC-G and the TAU polymorphism CA3662 was observed. For this 2-allele system, PDC and ALS cases were significantly less likely than Guamanian controls to have the 1 allele (4.9% and 2% vs 11.5%, respectively; Fisher exact P =.007). DNA sequence analysis of TAU coding regions did not demonstrate a mutation responsible for ALS-G-PDC-G. Analysis of TAU genotypes in an extended pedigree of subjects from Umatac showed obligate recombinants between TAU and ALS-G-PDC-G. Linkage analysis of the Umatac pedigree indicates that TAU is not the major gene for ALS-G-PDC-G.
Conclusions: The genetic association between ALS-G-PDC-G implicates TAU in the genetic susceptibility to ALS-G-PDC-G. TAU may be a modifying gene increasing risk for ALS-G-PDC-G in the presence of another, as yet, unidentified gene.