Accrued somatic mutations (nucleic acid changes) trigger ALS: 2005-2015 update

De novo mutations in SOD1 are a cause of ALS

OBJECTIVE

The only identified cause of amyotrophic lateral sclerosis (ALS) are mutations in a number of genes found in familial cases but also in sporadic cases. De novo mutations occurring in a parental gonadal cell, in the zygote or postzygotic during embryonal development can result in an apparently sporadic/isolated case of ALS later in life. We searched for de novo mutations in SOD1 as a cause of ALS.

METHODS

We analysed peripheral-blood exome, genome and Sanger sequencing to identify deleterious mutations in SOD1 in 4000 ALS patients from Germany, South Korea and Sweden. Parental kinship was confirmed using highly polymorphic microsatellite markers across the genome. Medical genealogical and clinical data were reviewed and compared with the literature.

RESULTS

We identified four sporadic ALS cases with de novo mutations in SOD1. They aggregate in hot-spot codons earlier found mutated in familial cases. Their phenotypes match closely what has earlier been reported in familial cases with pathogenic mutations in SOD1. We also encountered familial cases where de novo mutational events in recent generations may have been involved.

CONCLUSIONS

De novo mutations are a cause of sporadic ALS and may also be underpinning smaller families with few affected ALS cases. It was not possible to ascertain if the origin of the de novo mutations was parental germline, zygotic or postzygotic during embryonal development. All ALS patients should be offered genetic counselling and genetic screening, the challenges of variant interpretation do not outweigh the potential benefits including earlier confirmed diagnosis and possible bespoken therapy.

Olfactory Function in Latino Farmworkers Over 2 Years: Longitudinal Exploration of Subclinical Neurological Effects of Pesticide Exposure

OBJECTIVE

We compared patterns of olfactory function over 2 years in pesticide-exposed male Latino farmworkers and male Latino workers in industries without pesticide exposure.

METHODS

At five points over 2 years, workers completed tests of odor threshold (16 concentrations of n-butanol) using a well-established methodology. Tests at two or more time points were completed by 156 farmworkers and 118 non-farmworkers.

RESULTS

Farmworkers required significantly higher odorant concentrations at Contact 1 and across the 2-year follow-up to detect the odor. When adjusted for Contact 1, between-group differences persisted, but odor threshold performance did not worsen over time.

CONCLUSIONS

Pesticide exposure has been linked to neurodegenerative disease, as has declining olfactory function. Persistently poorer olfactory function among pesticide-exposed workers suggests the need to monitor neurological function in this vulnerable worker population.

Amyotrophic Lateral Sclerosis and Exposure to Diesel Exhaust in a Danish Cohort

Previous studies have suggested an increased risk of amyotrophic lateral sclerosis (ALS) and other motor neuron diseases for persons in occupations commonly involving exposure to diesel exhaust (DE). In this study, we investigated the association between occupational exposure to DE and odds of ALS. ALS cases were identified from the Danish National Patient Registry (1982-2013) and individually matched to 100 controls per case on the basis of birth year and sex. Using information on occupational history from 1964 onward obtained from the Danish Pension Fund, we estimated cumulative DE exposures using a job exposure matrix. We evaluated associations using conditional logistic regression analyses and stratified the analyses by sex. Using a 10-year lag period, DE exposure was positively associated with ALS among men who had ever been exposed (adjusted odds ratio (aOR) = 1.20, 95% confidence interval (CI): 1.05, 1.38). For men with greater than 50% probability of DE exposure, we observed a positive association between ALS and highest-quartile exposure during the 5-year (aOR = 1.35, 95% CI: 1.07, 1.70) and 10-year (aOR = 1.41, 95% CI: 1.11, 1.79) lag periods. Our study suggests an association between consistently higher exposures to DE and ALS in men, but not in women. These findings support previous reports of associations between ALS and occupations commonly involving DE exposure.

Ethics of clinical research in patients with ALS: is there a risk of exploitation?

Amyotrophic lateral sclerosis is the most common degenerative disease of the motor neuron network. Due to its inevitably fatal outcome, numerous attempts have been made to ameliorate its course. The emergence of every new technology has spurred research to see if it might benefit patients with ALS (PALS). This paper suggests a detailed road map to be followed when performing clinical research in PALS to satisfy the ethics requirements of the Declaration of Helsinki, expressed using the terminology of Beauchamp and Childress. The ethics principles that need to be satisfied are arranged in a hierarchical manner, each having to be satisfied before the next is approached: Justice; Beneficence, Nonmaleficence, Professional-Patient Relationship, and Respect for Autonomy. Study participants' autonomy can be respected only when all other principles have been addressed before PALS are approached to participate. Five 'red flags' are identified, which, if present, might indicate a risk that PALS may be exploited. PALS who are contemplating new treatments or clinical trials and their families will be assured that their best interests are the only ones that matter whenever adherence to established ethics principles and avoidance of known pitfalls are made explicit.

Puzzles in modern biology. IV. Neurodegeneration, localized origin and widespread decay

The motor neuron disease amyotrophic lateral sclerosis (ALS) typically begins with localized muscle weakness. Progressive, widespread paralysis often follows over a few years. Does the disease begin with local changes in a small piece of neural tissue and then spread? Or does neural decay happen independently across diverse spatial locations? The distinction matters, because local initiation may arise by local changes in a tissue microenvironment, by somatic mutation, or by various epigenetic or regulatory fluctuations in a few cells. A local trigger must be coupled with a mechanism for spread. By contrast, independent decay across spatial locations cannot begin by a local change, but must depend on some global predisposition or spatially distributed change that leads to approximately synchronous decay. This article outlines the conceptual frame by which one contrasts local triggers and spread versus parallel spatially distributed decay. Various neurodegenerative diseases differ in their mechanistic details, but all can usefully be understood as falling along a continuum of interacting local and global processes. Cancer provides an example of disease progression by local triggers and spatial spread, setting a conceptual basis for clarifying puzzles in neurodegeneration. Heart disease also has crucial interactions between global processes, such as circulating lipid levels, and local processes in the development of atherosclerotic plaques. The distinction between local and global processes helps to understand these various age-related diseases.