Pathologic evidence that the T188R mutation in PRNP is associated with prion disease.

Human prion diseases can be caused by mutations in the prion protein gene PRNP. Prion disease with mutations at codon 188 has been reported in 6 cases, but only 1 had the T188R mutation and it was not pathologically confirmed. We report the clinical, neuropsychologic, imaging, genetic, and neuropathologic features of a patient with familial Creutzfeldt-Jakob disease, associated with a very rare PRNP mutation at T188R. The patient presented with prominent behavioral changes in addition to the more typical cognitive and motorimpairments seen in sporadic Creutzfeldt-Jakob disease. The autopsy confirmed prion disease pathology. This case supports the pathogenicity of the T188 PRNP mutation, demonstrates the variability of clinical phenotypes associated with certain mutations, and emphasizes the importance of testing for genetic prion disease in cases of apparently sporadic atypical dementia.

Correlating DWI MRI with pathologic and other features of Jakob-Creutzfeldt disease.

Diffusion-weighted (DWI) magnetic resonance imaging (MRI) is a highly sensitive and specific test for diagnosis of sporadic Jakob-Creutzfeldt disease (sCJD); however, the neuropathologic origin of DWI signal abnormalities including other clinical features has not been well defined. We describe a case of sCJD with brain MRI taken 15 days before death, which provided an opportunity to correlate clinical, electroencephalogram, MRI, and neuropathologic findings to better understand which sCJD-specific neuropathologic changes underlie the DWI abnormalities. Clinical findings correlated well with both electroencephalogram and MRI changes. Neuropathologic analysis showed that hyperintensities on DWI MRI correlated best with the vacuolation score (r=0.78, P=0.0005) and PrP(Sc) load (r=0.77; P=0.0006), followed by reactive astrocytic gliosis (r=0.63, P=0.008). This case provides further evidence that DWI abnormalities correlate well with the clinical features and with PrP(Sc) accumulation and vacuolation.

A gamma-secretase inhibitor and quinacrine reduce prions and prevent dendritic degeneration in murine brains.

In prion-infected mice, both the Notch-1 intracellular domain transcription factor (NICD) and the disease-causing prion protein (PrP(Sc)) increase in the brain preceding dendritic atrophy and loss. Because the drug LY411575 inhibits the gamma-secretase-catalyzed cleavage of Notch-1 that produces NICD, we asked whether this gamma-secretase inhibitor (GSI) might prevent dendritic degeneration in mice with scrapie. At 50 d postinoculation with Rocky Mountain Laboratory (RML) prions, mice were given GSI orally for 43-60 d. Because we did not expect GSI to produce a reduction of PrP(Sc) levels in brain, we added quinacrine (Qa) to the treatment regimen. Qa inhibits PrP(Sc) formation in cultured cells. The combination of GSI and Qa reduced PrP(Sc) by approximately 95% in the neocortex and hippocampus but only approximately 50% in the thalamus at the site of prion inoculation. The GSI plus Qa combination prevented dendritic atrophy and loss, but GSI alone did not. Even though GSI reduced NICD levels to a greater extent than GSI plus Qa, it was unable to prevent dendritic degeneration. Whether a balance between NICD and dendrite growth-stimulating factors was achieved with GSI plus Qa but not GSI alone remains to be determined. Although the combination of GSI and Qa diminished PrP(Sc) in the brains of RML-infected mice, GSI toxicity prevented us from being able to assess the effect the GSI plus Qa combination on incubation times. Whether less toxic GSIs can be used in place of LY411575 to prolong survival remains to be determined.

Diagnosis of human prion disease.

With the discovery of the prion protein (PrP), immunodiagnostic procedures were applied to diagnose Creutzfeldt-Jakob disease (CJD). Before development of the conformation-dependent immunoassay (CDI), all immunoassays for the disease-causing PrP isoform (PrPSc) used limited proteolysis to digest the precursor cellular PrP (PrPC). Because the CDI is the only immunoassay that measures both the protease-resistant and protease-sensitive forms of PrPSc, we used the CDI to diagnose human prion disease. The CDI gave a positive signal for PrPSc in all 10-24 brain regions (100%) examined from 28 CJD patients. A subset of 18 brain regions from 8 patients with sporadic CJD (sCJD) was examined by histology, immunohistochemistry (IHC), and the CDI. Three of the 18 regions (17%) were consistently positive by histology and 4 of 18 (22%) by IHC for the 8 sCJD patients. In contrast, the CDI was positive in all 18 regions (100%) for all 8 sCJD patients. In both gray and white matter, approximately 90% of the total PrPSc was protease-sensitive and, thus, would have been degraded by procedures using proteases to eliminate PrPC. Our findings argue that the CDI should be used to establish or rule out the diagnosis of prion disease when a small number of samples is available as is the case with brain biopsy. Moreover, IHC should not be used as the standard against which all other immunodiagnostic techniques are compared because an immunoassay, such as the CDI, is substantially more sensitive.