Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset disease in which motor neurons in the brain and spinal cord degenerate by largely unknown mechanisms. ALS is familial (FALS) in 10% of cases, and the inheritance is usually dominant, with variable penetrance. Mutations in copper/zinc super oxide dismutase (SOD1) are found in 20% of familial and 3% of sporadic ALS cases. Five families with ALS and frontotemporal dementia (ALS-FTD) are linked to 9q21, whereas one family with pure ALS is linked to 18q21. We identified two large European families with ALS without SOD1 mutations or linkage to known FALS loci and conducted a genomewide linkage screen using 400 microsatellite markers. In both families, two-point LOD scores >1 and a haplotype segregating with disease were demonstrated only across regions of chromosome 16. Subsequent fine mapping in family 1 gave a maximum two-point LOD score of 3.62 at D1683137 and a three-point LOD score of 3.85 for markers D168415 and D1683137. Haplotype analysis revealed no recombination >∼30 cM, (flanking markers at D1683075 and D1683112). The maximum two-point LOD score for family 2 was 1.84 at D168415, and the three-point LOD score was 2.10 for markers D168419 and D168415. Definite recombination occurred in several individuals, which narrowed the shared haplotype in affected individuals to a 10.1-cM region (flanking markers: D1683396 and D1683112). The region shared by both families on chromosome 16q12 corresponds to ∼4.5 Mb on the Marshfield map. Bioinformatic analysis of the region has identified 18 known genes and 70 predicted genes in this region, and sequencing of candidate genes has now begun.
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