Acta Neuropathol (2009) 118:659–671 Fig. 6 a A ‘‘grape-like’’ focus of spongiform degeneration with large conﬂuent vacuoles surrounded by typical spongiform degeneration with ﬁne, relatively small vacuoles in sCJD MM 1?2C (hematoxylin and eosin 9200, frontal cortex); b focal perivacuolar staining surrounded by a synaptic pattern of PrP immunoreactivity (9200) in the cerebral cortex of a sCJD MM 1?2C; c spongiform degeneration with large vacuoles (hematoxylin and eosin 9200) and d perivacuolar PrP deposition (9200) in the cerebral cortex of a sCJD MV 2K Fig. 7 Regional distribution of the coarse/perivacuolar pattern of PrPSc deposition in 40 MM/MV 1?2C cases divided in 3 groups according to the number of regions showing the perivacuolar pattern in individual cases. For each group, the % of cases revealing the perivacuolar pattern in each brain region is shown. FC frontal cortex, TC temporal cortex, PC parietal cortex, OCC occipital cortex, Limbic CTX limbic cortices, Hipp ? AMG hippocampus?amygdala, STR striatum, HYP hypothalamus, TH thalamus, BRST brainstem, CE cerebellum 667 of the two protein types (Tables 4, 5). Clinical signs in MM/MV 1?2C with a limited PrPSc type 2 deposition (up to 5 brain regions involved) did not signiﬁcantly differ from those of MM/MV 1, but the disease duration became signiﬁcantly longer and cerebellar signs less frequent at onset with increasing type 2 load. Thus, MM/MV 2C?1 subjects showed both a disease duration and relative fre- quency of symptoms at onset consistent with those of sCJD MM/MV 2C. Age at onset and disease duration in VV 2?1 subjects were consistent with those of sCJD VV2, but the relative frequency of cognitive decline at onset was higher than in VV2 cases, although the difference was not statis- tically signiﬁcant, probably because of the low number of VV 2?1 cases. Last, clinical features in the 2 MV 2K?1 subjects were within the spectrum of the MV 2K group. Discussion Previous studies have addressed the issue of PrPSc types 1 and 2 co-occurrence in sCJD. Most of them raised the question of the inﬂuence of the number of cases and brain areas analyzed and emphasized the possibility that the co- occurrence of PrPSc types 1 and 2 is underestimated [13, 18, 20, 30, 37, 40, 43]. On the other hand, the use of a novel, potentially very sensitive approach, later shown to have pitfalls related to the detection of unspeciﬁc bands 123