During the past two decades, significant progress has been made in understanding the molecular genetic basis of human genetic diseases, the current next-generation sequencing technologies allowing gene identification even in single families. The future challenge is to translate this knowledge into the benefit of patients by producing novel methods for diagnostics, prevention and treatment. Progressive myoclonus epilepsies (PME) are rare, inherited, and usually childhood-onset neurodegenerative diseases whose core symptoms are epileptic seizures and debilitating involuntary muscle twitching (myoclonus). After the identification of mutations in the cystatin B encoding gene as the underlying cause for the most common single form of PME, Unverricht-Lundborg disease in 1996, over 25 genes associated with PME have been identified. In this talk, we will give on overview on the current molecular genetic understanding of PMEs culminating in our recent identification of a recurrent de novo mutation in the KCNC1 gene as a major cause of PME. We will review work on cystatin B aiming at understanding its physiological function and disease mechanisms in Unverricht-Lundborg disease. We will shortly discuss the possibly unifying mechanism underlying PME and prospects for precision medicine approaches.