Chromosomal copy number association studies in patients with amyotrophic lateral sclerosis (ALS) using blood DNA have so far been inconclusive. We employed genome-wide screening to look for copy number imbalances (CNIs) between blood and hair DNA from three ALS-discordant monozygotic twin pairs and two phenotypically normal monozygotic twin pairs. Genome-wide chromosomal copy number was estimated using AffyMetrix 6.0 GeneChips. CNIs were sought both between twin pairs and between blood and hair DNA from the same individuals. Two blood CNIs were found in one ALS-discordant twin pair. In another ALS-discordant twin pair, seven hair CNIs were detected. CNIs were also found between blood and hair in three individuals. Imbalances in blood copy number appear to be rare in monozygotic twin pairs, but hair may harbour more CNIs than blood. Copy number differences between blood and hair from the same individuals appear to be common. Since brain and hair share a common ectodermal origin, hair may be a more suitable tissue than blood to estimate somatic copy number variation in the brain.
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