Late-onset myoclonic epilepsy is being increasingly recognized as a late complication in elderly patients with Down syndrome (DS) in association with cognitive decline. This specific syndrome bears some broad clinical and EEG similarities to the progressive myoclonic epilepsies, particularly Unverricht-Lundborg disease (ULD). Our aim was to investigate a possible shared patho-genetic mechanism for clinico-physiological similarities in these different genetic syndromes. Two patients diagnosed with DS and late-onset myoclonic epilepsy were included in the study. Dodecamer repeats and other possible CSTB gene mutations were investigated after isolation of DNA from their blood samples. No dodecamer repeats and point mutations could be found. Our study did not show any mutations of EPM1 gene on chromosome 21 but these findings could not exclude a shared genetic mechanism in these syndromes.