High rate of constitutional chromosomal rearrangements in apparently sporadic ALS

Genetics of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating, uniformly lethal degenerative disorder of motor neurons that overlaps clinically with frontotemporal dementia (FTD). Investigations of the 10% of ALS cases that are transmitted as dominant traits have revealed numerous gene mutations and variants that either cause these disorders or influence their clinical phenotype. The evolving understanding of the genetic architecture of ALS has illuminated broad themes in the molecular pathophysiology of both familial and sporadic ALS and FTD. These central themes encompass disturbances of protein homeostasis, alterations in the biology of RNA binding proteins, and defects in cytoskeletal dynamics, as well as numerous downstream pathophysiological events. Together, these findings from ALS genetics provide new insight into therapies that target genetically distinct subsets of ALS and FTD.

A large genome scan for rare CNVs in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease selectively affecting motor neurons in the brain and spinal cord. Recent genome-wide association studies (GWASs) have identified several common variants which increase disease susceptibility. In contrast, rare copy-number variants (CNVs), which have been associated with several neuropsychiatric traits, have not been studied for ALS in well-powered study populations. To examine the role of rare CNVs in ALS susceptibility, we conducted a CNV association study including over 19,000 individuals. In a genome-wide screen of 1875 cases and 8731 controls, we did not find evidence for a difference in global CNV burden between cases and controls. In our association analyses, we identified two loci that met our criteria for follow-up: the DPP6 locus (OR = 3.59, P = 6.6 × 10(-3)), which has already been implicated in ALS pathogenesis, and the 15q11.2 locus, containing NIPA1 (OR = 12.46, P = 9.3 × 10(-5)), the gene causing hereditary spastic paraparesis type 6 (HSP 6). We tested these loci in a replication cohort of 2559 cases and 5887 controls. Again, results were suggestive of association, but did not meet our criteria for independent replication: DPP6 locus: OR = 1.92, P = 0.097, pooled results: OR = 2.64, P = 1.4 × 10(-3); NIPA1: OR = 3.23, P = 0.041, pooled results: OR = 6.20, P = 2.2 × 10(-5)). Our results highlight DPP6 and NIPA1 as candidates for more in-depth studies. Unlike other complex neurological and psychiatric traits, rare CNVs with high effect size do not play a major role in ALS pathogenesis.

Identification of candidate genes for sporadic amyotrophic lateral sclerosis by array comparative genomic hybridization

Amyotrophic lateral sclerosis (ALS) is a devastating disorder of the central nervous system that leads to progressive loss of upper and lower motor neurons. Most cases are sporadic and of unknown aetiology. In this study, we screened 72 patients with sporadic ALS for the presence of DNA copy number variations, in order to identify novel candidate disease genes. We have used sub-megabase resolution BAC array comparative genomic hybridization to detect genomic imbalances in our ALS patient cohort. Aberrations with potential relevance for disease aetiology were verified by oligo array CGH. In 72 patients with sporadic ALS, we identified a total of six duplications and five deletions that scored above our threshold. Nine of these 11 variations were smaller than 1Mb, and five were observed exclusively in ALS patients. In conclusion, non-polymorphic sub-microscopic duplications and deletions observable by array CGH are frequent in patients with sporadic ALS. Analysis of such aberrations serves as a starting point in deciphering the aetiology of this complex disease, given that affected genes can be considered candidates for influencing disease susceptibility.

Copy-number variation in sporadic amyotrophic lateral sclerosis: a genome-wide screen

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterised by the selective death of motor neurons in the brain and spinal cord. Genetic risk factors have been implicated in susceptibility to ALS. Like single nucleotide polymorphisms (SNPs), copy-number variants (CNVs) are a source of genetic variation that have important effects on gene expression and disease phenotypes, and our aim was to identify CNVs that predispose to sporadic ALS.

METHODS

We did a genome-wide screen for CNVs by analysis of Illumina 317K SNP arrays for 406 patients with sporadic ALS and 404 controls. We examined CNVs for association with ALS, and used the Kyoto Encyclopedia of Genes and Genomes database and the Gene Ontology database to investigate the functionality of genes that were deleted exclusively in patients with ALS.

FINDINGS

We detected 2328 CNVs in 810 individuals. No CNV locus was significantly associated with sporadic ALS. 406 genes were duplicated or deleted exclusively in patients with ALS and have not been reported in previous studies of CNVs. Of the 390 genes heterozygously deleted in patients with sporadic ALS, 155 (40%) deletions were recorded exclusively in patients. By contrast, of the 323 genes heterozygously deleted in control participants, only 51 (16%) were exclusive to the controls (p=2.15 x 10(-12) for difference between groups). Products of the genes deleted specifically in patients with sporadic ALS include proteins involved in oxidative phosphorylation, regulation of the actin cytoskeleton, and interactions between cytokines and their receptors.

INTERPRETATION

Common CNVs in the regions of the genome represented on the SNP array are unlikely to be associated with sporadic ALS. However, the high number of genes deleted specifically in patients with ALS strongly suggests that multiple rare deletions might have an important role in ALS pathogenesis.

Autoimmune diseases in a Danish cohort of 4,866 carriers of constitutional structural chromosomal rearrangements

OBJECTIVE

Constitutional structural chromosomal rearrangements (CSCRs) have facilitated the identification of genes associated with early-onset monogenic disorders and, more recently, genes associated with common and late-onset disorders. In an attempt to find genetic clues to their etiologies, we studied the risk of autoimmune diseases in a Danish cohort of CSCR carriers.

METHODS

We followed up 4,866 CSCR carriers over 71,230 person-years (1980 through 2004) for autoimmune diseases recorded in the Danish Hospital Discharge Register. Standardized incidence ratios (SIRs) and 95% confidence intervals (95% CIs) served as measures of the relative risk. To identify possible candidate loci for autoimmune diseases, the reported chromosomal breakpoints and deletions in CSCR carriers who developed autoimmune diseases were compared with previously suggested loci for these diseases.

RESULTS

The overall risk of any autoimmune disease among CSCR carriers was inconspicuous (SIR 1.2 [95% CI 0.95-1.5]; n = 74 cases observed versus 61.3 expected), but carriers of rearrangements involving chromosomes 2, 19, and 21 were at significantly increased risk. For the specific autoimmune diseases studied, cohort members were at significantly increased risk of Dupuytren's contracture, pernicious anemia, and juvenile rheumatoid arthritis (JRA). Sixteen carriers who developed an autoimmune disease had a chromosomal breakpoint or deletion coinciding with a previously suggested locus, including deletions 18p11, 18q22, and 22q11 associated with JRA.

CONCLUSION

CSCR carriers do not have a generalized predisposition to autoimmune diseases. However, we confirmed a number of reported susceptibility loci for JRA, and we suggest new susceptibility loci on chromosomes 5 and 11 for Dupuytren's contracture, and 19p13 as a possible shared susceptibility locus for a range of autoimmune diseases.

Genetics of familial and sporadic amyotrophic lateral sclerosis

Diseases affecting motor neurons, such as amyotrophic lateral sclerosis (Lou Gerhig's disease), hereditary spastic paraplegia and spinal bulbar muscular atrophy (Kennedy's disease) are a heterogeneous group of chronic progressive diseases and are among the most puzzling yet untreatable illnesses. Over the last decade, identification of mutations in genes predisposing to these disorders has provided the means to better understand their pathogenesis. The discovery 13 years ago of SOD1 mutations linked to ALS, which account for less than 2% of total cases, had a major impact in the field. However, despite intensive research effort, the pathways leading to the specific motor neurons degeneration in the presence of SOD1 mutations have not been fully identified. This review provides an overview of the genetics of both familial and sporadic forms of ALS.

Frequency of a tau genotype in amyotrophic lateral sclerosis

We investigated the susceptibility of the dinucleotide polymorphism A0 in the tau gene to amyotrophic lateral sclerosis (ALS). In 416 unrelated patients with ALS and 242 control subjects the A0/A0 genotype was not associated with the pooled sample of ALS cases. Subgroup analysis revealed that in sporadic ALS the A0 polymorphism was significantly overrepresented. There was no association of the A0/A0 genotype with the age and site of disease onset or the presence of dementia. The studied tau genotype may contribute to the multifactorial genetic background of ALS.

Measures and markers in amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disorder characterized by loss of spinal and cortical motor neurons, leading to progressive weakness and ultimately, death. Clinically, there appears to be an anatomic focus at disease onset, from which the disease then spreads. Because the focus of initial symptoms and the subsequent direction of spread can vary from patient to patient, disease monitoring is difficult, especially in a clinical trial, in which outcome measures must be identical and able to capture progression of all types. Thus, the search for markers of disease progression is especially important in ALS. Many approaches have been taken, from voluntary strength assessment and functional rating scales to physiological and pathological sampling of affected portions of nervous system. No proposed marker has been demonstrated to meet the desired criteria of biological meaning, sensitivity to disease progression, clear relationship to overall prognosis and survival, and ease of measurement. However, progress is being made in all of these regards.

Chromosomal translocation t(18;21)(q23;q22.1) indicates novel susceptibility loci for frontotemporal dementia with ALS

A chromosomal translocation t(18;21)(q23;q22) is reported in a patient with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). We exclude the physical involvement and silencing of the ALS-linked gene for copper/zinc superoxide dismutase (SOD1) on chromosome 21q22.1. The breakpoints are assigned to sequences flanked by the markers ATA1H06, D18S462, D21S1915, and D21S1898. These critical regions may contain susceptibility loci for FTD associated with ALS.