Approximately 10–15% of human prion diseases are genetically determined, caused by point mutations or additional octapeptide repeat insertions (OPRI) in the codifying region of the prion protein gene (PRNP).1 The normal prion protein has a repeat region between residues 51 and 91, which comprises a nonapeptide followed by a tandem repeat of four copies of an octapeptide. The prion proteins with additional OPRI are more prone to aggregate and the degree and kinetics of aggregation are proportional to the number of inserts. Mutations of up to nine additional OPRI within the PRNP gene have been characterized. 1, 2 or 3-OPRI are single case reports, whereas 4-OPRI or larger have been described in families with high penetrance.1 Up to now, molecular evidence of de novo events in patients with OPRI in PRNP has not been reported.

The aim of this study was to describe a well-documented case of a de novo 9-OPRI in PRNP presenting as a sporadic young-onset dementia.

CASE REPORT

The proband was a 34-year-old man who had had cognitive decline for six years. About the age of 28 years, he started losing creativity and having difficulties expressing himself. At the age of 31 years, his parents detected he was having difficulties with calculation, occasional stuttering, difficulties with word finding and spatial …