P525L FUS mutation is consistently associated with a severe form of juvenile amyotrophic lateral sclerosis

Truncating mutations in FUS/TLS give rise to a more aggressive ALS-phenotype than missense mutations: a clinico-genetic study in Germany

BACKGROUND AND PURPOSE

Mutations in the FUS/TLS have been associated with amyotrophic lateral sclerosis (ALS) in a few percent of patients.

METHODS

We screened 184 familial (FALS) and 200 sporadic German patients with ALS for FUS/TLS mutations by sequence analysis of exons 5, 6 and 13-15. We compared the phenotypes of patients with different FUS/TLS mutations.

RESULTS

We identified three missense mutations p.K510R, p.R514G, p.R521H, and the two truncating mutations p.R495X and p.G478LfsX23 in samples from eight pedigrees. Both truncating mutations were associated with young onset and very aggressive disease courses, whereas the p.R521H, p.R514G and in particular the p.K510R mutation showed a milder phenotype with disease durations ranging from 3 years to more than 26 years, the longest reported for a patient with a FUS/TLS mutation. Also, in a pair of monozygous twins with the p.K510R mutation, a remarkable similar disease course was observed.

CONCLUSIONS

Mutations in FUS/TLS account for 8.7% (16 of 184) of FALS in Germany. This is a higher prevalence than reported from other countries. Truncating FUS/TLS mutations result in a more severe phenotype than most missense mutations. The wide phenotypic differences have implications for genetic counselling.

De novo FUS gene mutations are associated with juvenile-onset sporadic amyotrophic lateral sclerosis in China

Juvenile amyotrophic lateral sclerosis (ALS) is a rare form of motor neuron disease and occurs before 25 years of age. Only very few sporadic cases of juvenile-onset ALS have been reported. Rare SOD1 mutations and several FUS mutations have been identified in juvenile-onset ALS patients. To define the genetics of juvenile-onset sporadic ALS (SALS) of Chinese origin, we sequenced all 5 exons of SOD1, exons 3-6 and 12-15 of FUS in 11 juvenile-onset SALS patients, 105 adult-onset ALS patients (including 6 familial ALS [FALS] pedigrees), and 245 healthy controls. For the 11 juvenile-onset SALS and 6 FALS cases, the other 7 exons of FUS were also screened. A heterozygous de novo missense mutation c.1574C>T (p.P525L), a heterozygous de novo 2-base pair deletion c.1509_1510delAG (p.G504Wfs*12), and a nonsense mutation c.1483C>T (p.R495X) was each identified in 1 juvenile SALS patient. A heterozygous missense mutation c.1561C>G (p.R521G) was identified in a FALS proband. In the Chinese population, the frequency of FUS mutation in FALS is 11.4% (95% confidence interval [CI], 0.9%-22.0%), higher than the Japanese (10%; 95% CI, 0.7%-19.3%), and Caucasians (4.9%; 95% CI, 3.9%-6.0%). The frequency of FUS mutation in SALS patients is 1.5% (95% CI, 0.2%-2.9%), which is similar to Koreans (1.6%; 95% CI, 0%-3.2%), but higher than in Caucasians (0.6%; 95% CI, 0.4%-0.8%). Our findings suggest that de novo FUS mutations are associated with juvenile-onset SALS of Chinese origin and that this gene should be screened in ALS patients with a young age of onset, aggressive progression, and sporadic occurrence.

FUS-related proteinopathies: lessons from animal models

The recent identification of ALS-linked mutations in FUS and TDP-43 has led to a major shift in our thinking in regard to the potential molecular mechanisms of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). RNA-mediated proteinopathy is increasingly being recognized as a potential cause of neurodegenerative disorders. FUS and TDP-43 are structurally and functionally similar proteins. FUS is a DNA/RNA binding protein that may regulate aspects of RNA metabolism, including splicing, mRNA processing, and micro RNA biogenesis. It is unclear how ALS-linked mutations perturb the functions of FUS. This review highlights recent advances in understanding the functions of FUS and discusses findings from FUS animal models that provide several key insights into understanding the molecular mechanisms that might contribute to ALS pathogenesis.