Fig. 1

The frequencies of non-expanded long C9orf72 hexanucleotide repeat intermediate-length alleles in three previous case-control studies in comparison with Finnish ALS cases and controls. ≥ 17 repeat alleles were found in 3.6% of the Finnish ALS cases, 2.6% of the controls (present study) and in 3.7% of cases with autopsy-proven corticobasal degeneration (CBD) as compared to 0.52% of the Global controls [3] and 1.9% for UK 58 Birth cohort [2]. The majority of cases were from three centers from USA and UK, while the controls were from a global study [23]. Allele frequencies for 58BC were obtained as personal written communication from Professor Simon Mead. Each ≥ 17 allele is presumed to be carried by one individual. ≥ 21 repeat alleles were found in 2.3% of the Finnish ALS cases and 1.7% of the controls (present study), and in 1.7% of CBD cases. These alleles were not reported in the Global controls [23]. 24–30 repeat alleles were found in 0.57% of the Finnish ALS cases and 0.76% of controls (present study),and in 0.5% of CBD cases and in 0.4% of ALS cases vs. 0.03% of controls in a recent meta-analysis [10]