Repeat expansions in AR, ATXN1, ATXN2 and HTT in Norwegian patients diagnosed with amyotrophic lateral sclerosis

Genetic repeat expansions cause neuronal degeneration in amyotrophic lateral sclerosis as well as other neurodegenerative disorders such as spinocerebellar ataxia, Huntington's disease and Kennedy's disease. Repeat expansions in the same gene can cause multiple clinical phenotypes. We aimed to characterize repeat expansions in a Norwegian amyotrophic lateral sclerosis cohort. Norwegian amyotrophic lateral sclerosis patients (n = 414) and neurologically healthy controls adjusted for age and gender (n = 713) were investigated for repeat expansions in AR, ATXN1, ATXN2 and HTT using short read exome sequencing and the ExpansionHunter software. Five amyotrophic lateral sclerosis patients (1.2%) and two controls (0.3%) carried ≥36 repeats in HTT (P = 0.032), and seven amyotrophic lateral sclerosis patients (1.7%) and three controls (0.4%) carried ≥29 repeats in ATXN2 (P = 0.038). One male diagnosed with amyotrophic lateral sclerosis carried a pathogenic repeat expansion in AR, and his diagnosis was revised to Kennedy's disease. In ATXN1, 50 amyotrophic lateral sclerosis patients (12.1%) and 96 controls (13.5%) carried ≥33 repeats (P = 0.753). None of the patients with repeat expansions in ATXN2 or HTT had signs of Huntington's disease or spinocerebellar ataxia type 2, based on a re-evaluation of medical records. The diagnosis of amyotrophic lateral sclerosis was confirmed in all patients, with the exception of one patient who had primary lateral sclerosis. Our findings indicate that repeat expansions in HTT and ATXN2 are associated with increased likelihood of developing amyotrophic lateral sclerosis. Further studies are required to investigate the potential relationship between HTT repeat expansions and amyotrophic lateral sclerosis.

Incidence and clinical features of amyotrophic lateral sclerosis in Møre and Romsdal County, Norway

BACKGROUND

To determine the annual incidence rate and clinical features of amyotrophic lateral sclerosis (ALS) in Møre and Romsdal County, Norway, in the 20-year period from 1988 to 2007.

METHODS

We recruited ALS patients retrospectively from the patient database of the two neurological departments in Møre and Romsdal County, Norway. The patients were identified by use of the international classification code for diseases. We recorded gender, age, municipality, symptoms, clinical signs, time from onset to diagnosis and death.

RESULTS

105 patients met the inclusion criteria. The crude annual incidence was 2.17 per 100,000 for the period 1988-2007. Gender-specific incidence for men was 2.32 per 100,000, and for women 2.03 per 100,000. Mean age at symptom onset was 66.8 ± 10.5 years. Mean interval from onset of symptoms to diagnosis was 13.5 ± 11.0 months, and mean survival time from diagnosis was 18.0 ± 22.0 months. Prevalence rate estimated on December 31, 2007 was 4.06 per 100,000.

CONCLUSION

The present study shows an annual incidence of ALS of similar magnitude to the previous studies from the Nordic countries during the past years. The short survival time corroborates prior studies, and is stable throughout the two studied decades.