Using case-parent trios to look for rare de novo genetic variants in adult-onset neurodegenerative diseases.

Rare de novo genetic variants have been detected in a number of diseases using case-parent trios. So far, trio studies have largely been confined to early-onset diseases where parent DNA samples are readily available. To test the feasibility of finding rare de novo variants in a typical late-onset neurodegenerative disease, we compared genome-wide copy number variants (CNVs) between patients with sporadic amyotrophic lateral sclerosis (SALS) and their unaffected parents. DNA from 12 SALS patients and their 24 parents was analysed for CNVs using AffyMetrix SNP 6.0 microarrays and Partek software. De novo CNVs (present in patients but not their parents) considered likely candidates for SALS were those that overlapped with CNS-related genes, were rare, or were found in multiple patients. All SALS patients had de novo CNVs. In 11 patients, 37 de novo CNVs fulfilled one or more criteria for a candidate region. Eleven de novo CNVs overlapped with genes, some of which are in pathways suspected in the pathogenesis of SALS. In conclusion, this pilot study shows that trios can be used to look for rare de novo genetic variants in patients with late adult-onset neurodegenerative disease. The results suggest that further studies of this nature with larger numbers of trios are warranted, but it is unusual to find surviving parents of offspring who have a late-onset neurodegenerative disease. An international collaborative effort will therefore be needed to collect sufficient numbers of such trios to reliably detect de novo mutations underlying these diseases.