Conference Coverage

Two Studies Probe Worldwide Ethnic Differences in ALS


 

References

WASHINGTON, DC—Two meta-analyses presented at the 67th Annual Meeting of the American Academy of Neurology examined the worldwide incidence, phenotype, and outcome of amyotrophic lateral sclerosis (ALS). Researchers found significant differences between European ALS incidence and incidence in East Asia (China and Japan), Central Asia (Iran), and West Asia (Israel). Conversely, they found homogeneity in incidence among populations from Europe, North America, and New Zealand. In a separate study, the same researchers found phenotypic heterogeneity of ALS at time of onset, time of diagnosis, in early follow-up, and in late follow-up. Additionally, ALS outcomes varied significantly, with a median survival time since onset ranging from 24 months (North Europe) to 48 months (South Asia).

In the first study, Benoît Marin, MD, MSc, of the University of Limoges in France, and colleagues performed a systematic review and meta-analysis of data concerning the differences in incidence of ALS with regard to ethnicity. Random effect meta-regression was conducted. Both crude and 2010 US gender and age-standardized incidence were considered. Subcontinent was used as a proxy for ethnicity. The researchers also gathered data from public genomic databases.

Of the 3,058 records reviewed, 78 population-based studies were selected, covering 40 geographical areas in 10 subcontinents. A total of 11,643 ALS cases and 737 million person-years of follow-up (PYFU) were considered.

The overall pooled worldwide crude incidence of ALS was at 1.78 per 100,000 PYFU; 1.72 after standardization on the 2010 US population. Significant differences have been reported between Europe and East Asia (China, Japan), Central Asia (Iran), and West Asia (Israel). Conversely, homogeneous rates have been reported in Caucasian populations from Europe, North America, and New Zealand. A more refined approach, involving genomic data, confirmed the positive association between ALS incidence and European ancestry (pooled USA standardized incidence: 1.85 for populations with European ancestry of 80% or more) and the negative association between ALS incidence and admixed populations or Asian ancestry (pooled USA standardized incidence: 0.83 for populations with Asian ancestry of 80% or more).

In a related study, Dr. Marin and colleagues examined ethnic differences in the phenotype and outcome of ALS. The researchers performed a systematic review, meta-analysis, and meta-regression of data with the aim of producing synthesized epidemiologic indicators. As in their other study, subcontinent was used as a proxy for ethnicity, and additional data were collected from public genomic databases.

Methodology was similar to the study previously discussed: 3,058 records were reviewed and 78 population-based studies were selected, covering 40 geographical areas in 10 subcontinents. Characteristics of about 12,700 ALS cases from population-based studies were considered.

Results highlighted the phenotypic heterogeneity of ALS at time of onset (age, sex ratio, bulbar onset), time of diagnosis (age, definite ALS according to El Escorial criteria), in early follow-up (comorbidities), and late follow-up (survival since onset or diagnosis). A major explanatory variable of the variability of ALS phenotype in population-based studies is subcontinent. Some markers of ALS phenotype have homogeneous distribution in western countries (sex ratio, mean age at onset or diagnosis), but their distribution in other subcontinents is remarkably different. Other markers present variations even in European subcontinents and in other continents (familial ALS, bulbar onset, definite ALS). As a consequence, ALS outcome varies significantly, with a median survival time since onset ranging from 24 months (North Europe) to 48 months (South Asia).

Dr. Marin and colleagues said that their research “sets the scene to sustain a collaborative study involving a wide international consortium in order to perform, with homogeneous methodology, an investigation of the link between ancestry, environment, and ALS incidence. Such an initiative should rely on wide geographical coverage, including populations with homogeneous ancestral origin, populations represented by different ancestries, and populations having a high degree of admixture from developed and resource-poor countries.”

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