In other facilities, both siblings had undergone karyotyping, measurement of urinary lactic acid and pyruvate levels, muscle biopsy, skin biopsy (negative for the accumulation of ceroid lipofuscin), search for NARP, MILS and MERRF mitochondrial DNA mutations in blood, genetic investigation for progressive myoclonic epilepsies, EMG (conduction velocity), jejunal biopsy for celiac disease and cystatin B gene analysis. Here, CSTB is linked to progressive myoclonus epilepsy.