Although only 5% of the human genome is conserved across mammals, a substantially larger portion is biochemically active, raising the question of whether the additional elements evolve neutrally or confer a lineage-specific fitness advantage. To address this question, we integrate human variation information from the 1000 Genomes Project and activity data from the ENCODE Project. A broad range of transcribed and regulatory nonconserved elements show decreased human diversity, suggesting lineage-specific purifying selection. Conversely, conserved elements lacking activity show increased human diversity, suggesting that some recently became nonfunctional. Regulatory elements under human constraint in nonconserved regions were found near color vision and nerve-growth genes, consistent with purifying selection for recently evolved functions. Our results suggest continued turnover in regulatory regions, with at least an additional 4% of the human genome subject to lineage-specific constraint.

Evidence of Abundant Purifying Selection in Humans for Recently Acquired Regulatory Functions

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease. The discovery of genes associated with amyotrophic lateral sclerosis, commencing with SOD1 in 1993, started fairly gradually. Recent advances in genetic technology have led to the rapid identification of multiple new genes associated with the disease, and to a new understanding of oligogenic and polygenic disease risk. The overlap of genes associated with amyotrophic lateral sclerosis with those of other neurodegenerative diseases is shedding light on the phenotypic spectrum of neurodegeneration, leading to a better understanding of genotype-phenotype correlations. A deepening knowledge of the genetic architecture is allowing the characterisation of the molecular steps caused by various mutations that converge on recurrent dysregulated pathways. Of crucial relevance, mutations associated with amyotrophic lateral sclerosis are amenable to novel gene-based therapeutic options, an approach in use for other neurological illnesses. Lastly, the exposome-the summation of lifetime environmental exposures-has emerged as an influential component for amyotrophic lateral sclerosis through the gene-time-environment hypothesis. Our improved understanding of all these aspects will lead to long-awaited therapies and the identification of modifiable risks factors. 

Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis

Genome-wide identification of the genetic basis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a complex disease centered on progressive death of motor neurons. Despite heritability estimates of 52%, GWAS studies have discovered only seven genome-wide significant hits. We developed a new machine learning approach called RefMap that integrates functional genomics with ALS genetics. Comprehensive transcriptomic and epigenetic profiling of iPSC-derived motor neurons enabled RefMap to identify 690 genes associated with ALS, the majority of which are novel. Extensive conservation, transcriptome and network analyses demonstrated the functional significance of these candidate genes in motor neurons and disease progression, and our genetic results support initiation of ALS neurotoxicity in the distal axon. KANK1 is enriched with coding and noncoding, common and rare ALS-associated variants. Reproducing patient KANK1 mutations in human neurons led to neurotoxicity with disruption of the distal axon. RefMap can be applied broadly to increase the discovery power in genetic association studies of human complex traits and diseases.

Genome-Wide Identification of the Genetic Basis of Amyotrophic Lateral Sclerosis

Rare Variant Burden Analysis within Enhancers Identifies CAV1 as an ALS Risk Gene

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease CAV1 and CAV2 organise membrane lipid rafts (MLR) important for cell signalling and neuronal survival, and overexpression of CAV1 ameliorates ALS phenotypes in vivo Genome-wide association studies localise a large proportion of ALS-risk variants within the non-coding genome, but further characterisation has been limited by lack of appropriate tools  Applying a new pipeline to identify pathogenic genetic variation within enhancer-elements responsible for regulating gene expression, we have discovered disease-associated variation within CAV1/CAV2 enhancers, which replicated in an independent cohort Discovered enhancer mutations reduce CAV1/CAV2 expression and disrupt MLR in patient-derived cells; and CRISPR/Cas9 perturbation proximate to a patient-mutation is sufficient to reduce CAV1/CAV2 expression in neurons Additional enrichment of ALS-associated mutations within CAV1 exons positions CAV1 as a new ALS gene We propose CAV1/CAV2 overexpression as a personalised medicine target for ALS

Samantha Allen

Papers

Rare Variant Burden Analysis within Enhancers Identifies CAV1 as an ALS Risk Gene

Rare Variant Burden Analysis within Enhancers Identifies CAV1 as a New ALS Risk Gene