Prion protein amyloidosis with divergent phenotype associated with two novel nonsense mutations in PRNP

Abstract

Stop codon mutations in the gene encoding the prion protein (PRNP) are very rare and have thus far only been described in two patients with prion protein cerebral amyloid angiopathy (PrP-CAA). In this report, we describe the clinical, histopathological and pathological prion protein (PrP(Sc)) characteristics of two Dutch patients carrying novel adjacent stop codon mutations in the C-terminal part of PRNP, resulting in either case in hereditary prion protein amyloidoses, but with strikingly different clinicopathological phenotypes. The patient with the shortest disease duration (27 months) carried a Y226X mutation and showed PrP-CAA without any neurofibrillary lesions, whereas the patient with the longest disease duration (72 months) had a Q227X mutation and showed an unusual Gerstmann-Sträussler-Scheinker disease phenotype with numerous cerebral multicentric amyloid plaques and severe neurofibrillary lesions without PrP-CAA. Western blot analysis in the patient with the Q227X mutation demonstrated the presence of a 7 kDa unglycosylated PrP(Sc) fragment truncated at both the N- and C-terminal ends. Our observations expand the spectrum of clinicopathological phenotypes associated with PRNP mutations and show that a single tyrosine residue difference in the PrP C-terminus may significantly affect the site of amyloid deposition and the overall phenotypic expression of the prion disease. Furthermore, it confirms that the absence of the glycosylphosphatidylinositol anchor in PrP predisposes to amyloid plaque formation.

Fig. 1

Sequence analysis of PRNP of patients 1 and 2. Short segments of PRNP of patient 1 with the Y226X mutation (upper part of figure) and of patient 2 with the Q227X mutation (lower part of figure) are shown. The insertion of either adenine (Y226X) or thymine (Q227X) causes a premature stop codon

Fig. 2

Histopathologic features of PRNP-Y226X. Sections are stained with haematoxylin–eosin (a, c), Luxol-periodic acid-Schiff reaction (e), 3F4 anti-PrP antibody (b, d, g), anti-phosphorylated tau (AT8) (f) and anti-Aβ (h). Original magnification ×100 (d), ×200 (a, b, c, h) and ×400 (e, f, g). Amyloid angiopathy involving small to medium-sized arteries, arterioles (arrow) and capillaries of the cerebral (a, b, g) and cerebellar cortex and leptomeninges (c, d). Spongiform changes in the parietal cortex with amyloid depositions surrounding blood vessels (e). Focal tau accumulations around blood vessels with amyloid depositions in the temporal cortex (f). Absence of staining with anti-Aβ antibodies (h)

Fig. 3

Histopathologic features of PRNP-Q227X. Sections are stained with haematoxylin–eosin (a), Luxol-periodic acid-Schiff reaction (c), 3F4 anti-PrP antibody (b, d) and anti-tau antibody RD4 (e, f). Original magnification ×200 (a, b, c, d) and ×400 (e, f). Presence of numerous multicentric and unicentric plaques in the frontal cortex (arrows) (a, b). Relative sparing of the cerebellum with sparse amyloid depositions (arrow) (c, d). Dystrophic neurites surrounding PrP^Sc plaques and neuropil threads (e) and neurofibrillary tangles (f)

Fig. 4

PrP^Sc typing and characterization of PRNP-Q227X. Immunoblot analysis of partially purified, detergent insoluble, abnormal PrP obtained from the frontal cortex of a sCJDVV2 case (lanes 1 and 3) and patient 2 (lanes 2, 4, 5). Samples are without (lanes 1, 2) or with a Proteinase K (PK) digestion step (lanes 3–5). The sample run in lane 5 was also deglycosylated with PNGaseF. Immunoblot was probed with 3F4. The smears in lanes 2, 4 and 5 likely represent incompletely solubilized (i.e. not monomeric) PrP-amyloid. Approximate molecular masses are in kilodaltons