Complex ocular choristomas in linear nevus sebaceus syndrome: a report of two cases

Two cases of linear nevus sebaceus syndrome (LNSS) are described in which ipsilateral facial nevus of Jadassohn was associated with complex ocular choristoma. One patient also had scleral osteomas, a rare occurrence in LNSS.

Long-segment substernal jejunal esophageal replacement with internal mammary vascular augmentation

We describe a technique that uses the internal mammary vessels to enhance long-segment jejunal graft blood supply in addition to an intact distal mesenteric vascular arcade. We believe that this technique, called vascular augmentation, improves jejunal graft perfusion and decreases ischemic complications.

PREEMPTIVE PROPHYLAXIS WITH A LIPID PREPARATION OF AMPHOTERICIN B FOR INVASIVE FUNGAL INFECTIONS IN LIVER TRANSPLANT RECIPIENTS REQUIRING RENAL REPLACEMENT THERAPY1

BACKGROUND

Posttransplant renal replacement therapy has been shown to be an independently significant risk factor for invasive fungal infections after liver transplantation. We assessed the efficacy of a lipid preparation of amphotericin B as prophylaxis for invasive fungal infections, directed toward liver transplant recipients requiring renal replacement therapy.

METHODS

A total of 148 patients transplanted between 1990 and 1997 received no antifungal prophylaxis. Since 1997, 38 patients underwent liver transplantation; antifungal prophylaxis with a lipid preparation of amphotericin B was used in patients requiring renal replacement therapy.

RESULTS

Fifteen percent (22 of 148) of the patients transplanted before 1997 required renal replacement therapy. In this cohort, the incidence of invasive fungal infections (36% vs. 7%, P=0.0007) and invasive aspergillosis (14% vs. 2%, P=0.02) was significantly higher in patients who required renal replacement therapy compared with those who did not. Since 1997, 29% (11 of 38) of the patients required renal replacement therapy and received antifungal prophylaxis. Invasive fungal infections occurred in 36% (8 of 22) of the patients who received no prophylaxis (patients before 1997), and 0% (0 of 11, P=0.03) in those who received antifungal prophylaxis (since 1997). Antifungal prophylaxis was independently associated with protection from fungal infection (P=0.017). No reduction in mortality with antifungal prophylaxis was documented.

CONCLUSION

Prophylaxis with a lipid preparation of amphotericin B was associated with a significant reduction in invasive fungal infections in high-risk liver transplant recipients, i.e., those requiring renal replacement therapy. However, no beneficial effect on survival could be documented.

Respiratory acidosis

Respiratory acidosis, or primary hypercapnia, is the acid-base disorder that results from an increase in arterial partial pressure of carbon dioxide. Acute respiratory acidosis occurs with acute (Type II) respiratory failure, which can result from any sudden respiratory parenchymal (eg, pulmonary edema), airways (eg, chronic obstructive pulmonary disease or asthma), pleural, chest wall, neuromuscular (eg, spinal cord injury), or central nervous system event (eg, drug overdose). Chronic respiratory acidosis can result from numerous processes and is typified by a sustained increase in arterial partial pressure of carbon dioxide, resulting in renal adaptation, and a more marked increase in plasma bicarbonate. Mechanisms of respiratory acidosis include increased carbon dioxide production, alveolar hypoventilation, abnormal respiratory drive, abnormalities of the chest wall and respiratory muscles, and increased dead space. Although the symptoms, signs, and physiologic consequences of respiratory acidosis are numerous, the principal effects are on the central nervous and cardiovascular systems. Treatment for respiratory acidosis may include invasive or noninvasive ventilatory support and specific medical therapies directed at the underlying pathophysiology.

Vitamin C augments chemotherapeutic response of cervical carcinoma HeLa cells by stabilizing P53

Human Papilloma Virus (HPV) is associated in most instances with cervical cancer. The HPV oncoproteins target P53 protein for degradation, leading to deregulation of cell cycle. We investigated whether stabilization of P53 in cervical cancer cells, by downregulating HPV transcription would restore the apoptotic ability of these cells. Our findings show that vitamin C downregulates the redox sensitive transcription factor AP-1 and decreases one of its transcription targets HPV E6, and stabilizes P53. This was associated with an increase in Bax and decrease in Bcl-2 and telomerase activity. Accumulation of P53 and its target gene bax then sensitized HeLa cells to cell-cycle arrest, cell death/apoptosis induced by cisplatin, and etoposide. Increasing drug sensitivity of cervical carcinoma cells by stabilizing P53 using vitamin C is a novel approach and has potential clinical relevance.

Post-Traumatic Cavernous Fistula Fed by Persistent Trigeminal Artery: Treatment by GDC Embolisation

SUMMARY

A case of traumatic persistent pnmltlve trigeminal artery (PPTA) cavernous sinus fistula treated with GDC embolisation is reported. Because of the small lumen of PP TA, posteriorly directed course and flow contribution from the posterior circulation, balloon embolisation via the carotid system was not considered appropriate. The fistula was successfully closed by GDC embolisation.

Telomerase-A molecular marker for cervical cancer screening

Cervical cancer is one of the most common cancers in women and can be routinely screened for by the Papanicolaou smear. Screening for HPV high-risk types 16 and 18 has augmented the sensitivity of this test, but still some cases remain undetected. We have investigated the utility of assaying telomerase activity as a possible screening marker for cervical cancer. Telomerase activity was studied in relation to HPV 16/18 infection, Papanicolaou smear cytopathology, and biopsy histopathology in a total of 88 subjects, consisting of 29 cervical cancer cases, 19 control hysterectomy samples, 16 precancerous cervical scrapes, 6 cervical samples from other gynecological malignancies, and 18 normal healthy cervical scrapings. Telomerase activity was detected in 96.5% of cervical tumor samples and in 68.7% of premalignant cervical scrapings but was not detected in control hysterectomy samples and in cervical scrapings of normal healthy controls. Telomerase assay had a diagnostic accuracy of 95.8 in tissue samples, 79.1 in scrapings and 91.2 in all. Whereas HPV-16/18 subtyping had a diagnostic accuracy of 89.5% in tissue samples, 70.5% in scrapings, and 82.1% in all. There was also 71% agreement between telomerase activity and HPV-16/18 infection. The absence of telomerase activity in cervical scrapes from healthy women indicated the potential of telomerase to serve as a good screening marker for the early diagnosis of cervical cancer. For the first time we have also shown the ability of telomerase to detect micro and probably occult metastasis in gynecological malignancies.

Preemptive therapy versus universal prophylaxis with ganciclovir for cytomegalovirus in solid organ transplant recipients

Whether preemptive therapy or universal prophylaxis with ganciclovir is the optimal approach against cytomegalovirus (CMV) remains unresolved. Controversy abounds with respect to the efficacy of preemptive therapy, the reliability of preemptive therapy tools, the logistical difficulties in conducting surveillance monitoring for CMV, the cost of prophylaxis, the effect of prophylaxis on indirect sequelae of CMV and epidemiology of CMV, and the potential for emergence of ganciclovir-resistant CMV. Although neither approach is wholly adequate, a discussion of the relative merits and limitations of the 2 approaches may guide the selection of a rational approach toward prevention of CMV infection in organ transplant recipients.

Complete vaginal prolapse: an unusual presentation of anovestibular fistula

An adolescent girl with an anovestibular fistula presenting as a complete vaginal prolapse and large-bowel obstruction is reported. The prolapse was reduced manually after repeated bowel washouts and a divided high sigmoid colostomy. The patient is awaiting posterior sagittal anorectoplasty. Possible etiopathologic factors of the prolapse are discussed. A vaginal prolapse in a patient with an anorectal malformation has not been reported previously in the English literature.

Differential sensitivity of murine myeloid FDC-P1 cells and apoptosis resistant mutant(s) to anticancer drugs

There is growing evidence which suggests that dysregulation of apoptosis may lead to several disease states including cancer. To investigate the mechanism controlling the induction of cell death, apoptosis defective/resistant (Apt-) mutants were isolated and characterized in this study. FDC-P1, a mouse myeloid cell line that depends upon IL-3 for survival and growth but undergoes apoptosis when deprived of growth factor, was mutagenized by treatment with ethyl methane sulfonate. We selected cells that survived the growth factor deprivation but did not grow without the factor. Surviving cells were cloned by limiting dilution and four clones that showed the least morphological characteristics and biochemical changes of apoptosis were chosen. Unlike the parent FDC-P1, these mutants were cross resistant to apoptosis induced by a variety of antitumor drugs such as Adriamycin, Dexamethasone, VP-16, as well as reactive oxygen species (ROS) generated by xanthine/xanthine oxidase (X/XO). We used one of these Apt- mutant to test candidate death genes. Our findings suggest that the preferential increase in Bax/Bcl-2 ratio, p53, c-Myc, Caspase-3 and decrease in AP-1 on treatment with various anticancer drugs may contribute to the preferential apoptotic response in FDC-P1 cells but to varying degrees. Whereas, the higher constitutive level of antioxidant enzymes superoxide dismutase and catalase in the Apt- mutant may contribute at least in part to its resistance.

Epidemiological applications: a case report of a village epidemic of gastroenteritis

This is a case report of an epidemic of gastroenteritis which was investigated and controlled by epidemiological methods only, before laboratory investigations could be done to confirm the original epidemiological conclusions--from contaminated home made ice-cubes. The case and process are reported in order to encourage similar uses of epidemiology by field public health practitioners, especially within the district or primary health care systems and particularly in places where laboratory support are difficult to avail. The case is used also to discuss the equipments and facilities that ought to be part of the support system for every modern field public health practitioner. These should include computers, modern communication facilities and epidemiological support systems, especially senior epidemiologists; as such senior personnel are available to junior colleagues in the other areas of specialist medical practice.

Teenage pregnancies in the Rewa medical sub-division, Fiji

To assess the magnitude of teenage pregnancies in the Rewa Medical Sub-division as well as the socio-demographic characteristics of the affected teenagers so as to provide a baseline for tackling the problem. The study was a 5 year retrospective study (1994-1998) of the medical records of the Nausori Maternity Unit, the only unit for these purposes in the entire Subdivision. Pregnancies that were intentionally terminated were not included, as no such data was available from these our public health services. An average of 11.1% of the 5319 obstetric patients attended to at the centre for the 5 years were teenagers. Their age range was 13 to 19 years. Proportionately more Fijians had such teenage pregnancies than their Indo-Fijian counterparts. The same was true of their being unmarried or being VDRL positive. A larger percentage of the Indian teenagers received assisted deliveries than the Fijians, but this was not statistically significant, being 6% and 4% respectively. Low birth weight was 19% among these teenagers (compared with 5.9% overall). Efforts are needed in the area of family life education to improve on aspects of teenage pregnancies. Since this is an area of education that has many conflicting values in the modern world, it is advocated that parents as well as many agencies as possible should be targets as well as join in this task in order meet the needs as due. Such education should cover and respect all the values concerned.

Acute ventricular rate control in atrial fibrillation: IV combination of diltiazem and digoxin vs. IV diltiazem alone

OBJECTIVE

To analyze the efficacy of an IV combination of diltiazem and digoxin vs IV diltiazem alone for acute ventricular rate control in patients with atrial fibrillation.

DESIGN

Prospective, randomized, open-label study.

PATIENTS AND METHODS

Fifty-two patients with atrial fibrillation and uncontrolled ventricular rates were randomized to receive either an IV combination of diltiazem and digoxin or IV diltiazem alone and were observed for 12 h. The successful rate control was defined as a ventricular rate < 100 beats per minute (bpm) persisting for 1 h or conversion to sinus rhythm. The loss of rate control was defined as an increase in the ventricular rate to > 100 bpm persistently for > 30 min or rebound to atrial fibrillation.

RESULTS

In both treatment arms (n = 26 each), all patients achieved successful and comparable ventricular rate control at 12 h. The mean (+/- SD) time taken to achieve successful rate control was shorter in the combination arm (15 +/- 16 vs. 22 +/- 22 min). Six patients in the combination arm and 11 in the diltiazem-alone arm experienced episodes of loss of rate control. This loss in the combination arm was less than that in the diltiazem-alone arm (14 vs 39 episodes; p = 0.05). The loss of rate control per patient in the combination arm was also less than that in the diltiazem-alone arm (2.0 +/- 1.0 vs. 3.5 +/- 1.9 episodes per patient; p = 0.04).

CONCLUSIONS

This study demonstrates that in patients with atrial fibrillation who have a rapid ventricular response, the IV combination of diltiazem and digoxin results in a more efficacious ventricular rate control with fewer fluctuations than that achieved by therapy with IV diltiazem alone.

Adenocarcinoma of the uterine cervix compared with squamous cell carcinoma: a 12-year study in Southampton and South-west Hampshire

In a 12-year study of the population of Southampton and South-west Hampshire (SSWH), there was no rise or fall in the incidence of adenocarcinoma of the uterine cervix, although the incidence of squamous cell carcinoma fell from 14 to 7.2 per 100000 women years and the overall fall in age-adjusted incidence of cervical carcinoma was commensurate with that of England and Wales. The majority (59%) of adenocarcinomas were seen in women aged less than 50, supporting the concept of a higher risk in young women. Screen-detected carcinomas accounted for 50% of adenocarcinomas and 41% of squamous cell carcinomas in women aged 20-64 (the difference was not significant). There were more screen-detected adenocarcinomas of less than 3 mm depth of invasion and 7 mm lateral extension during the third period of the study (1991-1993). The results are consistent with reports of an increased risk of cervical cancer in women born since 1940, and lesser effectiveness of screening in preventing adenocarcinoma compared with squamous cell carcinoma. High prevalence of early screen-detected carcinomas may have been a factor in recent reports of increased incidence of adenocarcinoma.

The role of Alzheimer's disease-related presenilin 1 in intercellular adhesion

Most cases of familial early-onset Alzheimer's disease are caused by mutations in the presenilin 1 (PS1) gene. However, the cellular functions of PS1 are unknown. We showed predominant localization of PS1 to cell-cell contacts of the plasma membrane in human prostate epithelial tissue and in a human epithelial cell line HEp2 stably transfected with an inducible PS1 construct. PS1 co-immunoprecipitated with beta-catenin from cell lysates of stable transfectants. Conversely, PS1 lacking the PS1-beta-catenin interaction site did not co-immunoprecipitate with beta-catenin and was not recruited to the cell-cell contacts. L cells, which do not form tight intercellular contacts, formed clusters of adhered cells after stable transfection with GFP-PS1 cDNA and demonstrated a clear preference for independent aggregation in the mixed cultures. However, L cells transfected with mutant GFP-PS1 constructs, which had a truncated N-terminus of PS1 or deleted PS1-beta-catenin interaction site, failed to form intercellular contacts. In addition, in primary cultures of mouse cortical neurons PS1 was highly concentrated on the surface of extended growth cones. Taken together, our results suggest an important role of PS1 in intercellular adhesion in epithelial cells and neurons.

Tracheal injury during endoscopic hemithyroidectomy

Unsuspected tracheal injury during endoscopic hemithyroidectomy is described. The diagnosis was delayed because of absent symptomatology. Surgical repair was planned but deferred because of infection. The patient was managed with a tracheostomy tube and antibiotics, and the wound healed completely without any residual abnormality or complications.

Posttransplantation dialysis-associated infections: morbidity and impact on outcome in liver transplant recipients

The aim of this study is to assess the predictors, impact on infectious morbidity, and outcome of posttransplantation dialysis in liver transplant recipients and to compare the results with data from patients who did not require dialysis after transplantation. The study sample included 176 consecutive patients undergoing liver transplantation; the median follow-up was 4.3 years. All patients were administered tacrolimus as primary immunosuppression. Overall, 16% (28 of 176 patients) of the patients required dialysis after transplantation. Patients requiring dialysis had significantly greater pretransplantation creatinine levels (2.4 v 1.2 mg/dL; P =.009), were more likely to require pretransplantation dialysis (21% v 1%; P =.0001), and had a greater rate of biopsy-proven rejection episodes (50%, 14 of 28 episodes v 20%, 30 of 148 episodes; P =.0009) and longer posttransplantation intensive care unit lengths of stay (P =.0001). The incidence of infections (91% v 41%; P =.0001) and episodes of infection per patient (2.4 v 0.7 episodes; P =.0001) were significantly greater in patients undergoing dialysis compared with those not undergoing dialysis. There was no difference in the frequency of cytomegalovirus (CMV) infection or disease; however, bacterial infections (87% v 31%; P =.0001) and invasive fungal infections (39% v 7%; P =.0001) were significantly more likely to occur in patients requiring dialysis. In logistic regression, dialysis (P =.0006) and CMV infection (P =.007) were independent significant predictors of major infections. Overall survival (assessed by Kaplan-Meier probability) was less in patients undergoing dialysis compared with those not undergoing dialysis (P =.0001). Among dialyzed patients, only 10% of those who survived had an invasive fungal infection compared with 46% of those who died (P =.08); 5 of 6 patients died within 1 month of the fungal infection. The need for dialysis portended a grave outcome in liver transplant recipients and identified a subgroup of patients at a significantly greater risk for major infections, particularly fungal infections, after liver transplantation.

Malaria during pregnancy and infancy, in an area of intense malaria transmission in central India

The clinico-epidemiological pattern of malarial infection in a cohort of pregnant women and infants was analysed during a malaria epidemic (1997-1998). The subjects were all members of tribal communities in an isolated and almost inaccessible area of central India. Overall, 151 (55%) of the 274 pregnant women investigated were found to have malarial infections at some time during the study, with Plasmodium falciparum predominating (88% of infections). All of the women investigated, whether primigravidae (42% found infected), secundigravidae (68%) or multigravidae (54%), were at great risk of developing severe malaria. When trimesters were compared, the highest prevalence of P. falciparum infection was recorded in the second (59% infected), irrespective of parity. Of the women found infected with P. falciparum, 3% had abortions, 4% stillbirths and 2% had babies who died while neonates. The small number of P. vivax infections observed prevented similar analyses for this species of parasite. Malarial infection was also seen in 218 (41%) of the 535 infants investigated. The values of age-specific prevalences revealed that > 30% of the infants examined at 2 months of age were then found to have P. vivax and/or P. falciparum parasitaemias. At 1 year of age, overall malaria prevalence was 50%, with P. vivax representing 25% of the infections and P. falciparum the rest. Subsequent follow-up revealed that three of the infants investigated, each of whom had had P. falciparum infections previously, died before their first birthdays. Re-infections (or treatment failures) were found to be common, both in the infants and the pregnant women. Pregnant women and infants from the study area clearly require systematic intervention to reduce their malaria-attributable morbidity.

Cryptococcus neoformans infection in organ transplant recipients: variables influencing clinical characteristics and outcome

Unique clinical characteristics and other variables influencing the outcome of Cryptococcus neoformans infection in organ transplant recipients have not been well defined. From a review of published reports, we found that C. neoformans infection was documented in 2.8% of organ transplant recipients (overall death rate 42%). The type of primary immunosuppressive agent used in transplantation influenced the predominant clinical manifestation of cryptococcosis. Patients receiving tacrolimus were significantly less likely to have central nervous system involvement (78% versus 11%, p =0.001) and more likely to have skin, soft-tissue, and osteoarticular involvement (66% versus 21%, p = 0.006) than patients receiving nontacrolimus- based immunosuppression. Renal failure at admission was the only independently significant predictor of death in these patients (odds ratio 16.4, 95% CI 1.9-143, p = 0.004). Hypotheses based on these data may elucidate the pathogenesis and may ultimately guide the management of C. neoformans infection in organ transplant recipients.

Evolving trends in multiple-antibiotic-resistant bacteria in liver transplant recipients: a longitudinal study of antimicrobial susceptibility patterns

The incidence, sources, impact on outcome, and temporal trends in multiple-antibiotic-resistant bacteria in liver transplant recipients over the last decade (from 1990 through 1999) were assessed. Of 165 consecutive patients who underwent transplantation, 31% (51 of 165 patients) had at least 1 infection caused by multiple-antibiotic-resistant bacteria. Overall, 69% (66 of 96 infections) of all bacterial infections were multiple-antibiotic resistant. Ninety-one percent (45 of 49 isolates) of the Staphylococcus aureus isolates, 50% (6 of 12 isolates) of the enterococci, and 54% of the gram-negative bacteria (47%; 7 of 15 Pseudomonas aeruginosa, and 60%; 12 of 20 Enterobacteriaceae) were multiple-antibiotic resistant. A significant trend toward an increase in infections caused by multiple-antibiotic-resistant bacteria (P =.003), largely caused by an increase in gram-positive infections, was documented through the decade. There was a significant increase in infections caused by methicillin-resistant S aureus (P =.0001) and vancomycin-resistant enterococci (P =.04) over time. The proportion of gram-negative isolates that were multiple-antibiotic resistant (P =.447) did not increase significantly over time. However, a strikingly high frequency of resistance to piperacillin or ceftazidime suggests that extended-spectrum beta-lactamase production in our Enterobacteriaceae may have been more prevalent than realized. Mortality at 1 year was significantly greater in patients with multiple-antibiotic resistant bacteria compared with all other patients (P =.001). These longitudinal trends have implications not only for guiding therapeutic practices, but ultimately for devising strategies to curtail multiple-antibiotic resistance in liver transplant recipients.

Chemopreventive activity ofWithania somnifera in experimentally induced fibrosarcoma tumours in Swiss albino mice

The current experimental work deals with the chemopreventive studies of a hydroalcoholic extract of Withania somnifera roots, against 20-methylcholanthrene induced fibrosarcoma tumours in Swiss albino mice. A single subcutaneous injection of 200 microg 20-methylcholanthrene in 0.1 mL of dimethylsulphoxide into the thigh region of mice produced a high incidence (96%) of tumours. Oral treatment of animals with 400 mg/kg body weight of Withania somnifera extract (one week before injecting 20-methylcholanthrene and continued until 15 weeks thereafter) significantly reduced the tumour incidence, tumour volume and enhanced the survival of the mice, compared with 20-methylcholanthrene injected mice. The tumour incidence was also delayed in the treatment group when compared with 20-methylcholanthrene injected mice. Liver biochemical parameters revealed a significant modulation of reduced glutathione, lipid peroxides, glutathione-S-transferase, catalase and superoxide dismutase in extract treated mice compared with 20-methylcholanthrene injected mice. The mechanism of chemopreventive activity of Withania somnifera extract may be due to its antioxidant and detoxifying properties.

Treatment of a molasses based distillery effluent in a constructed wetland in central India

A field-scale 4-celled, horizontal subsurface constructed wetland (CW) was installed to evaluate removal efficiencies of wastewater constituents in an industrial distillery effluent. Total and dissolved solids, NH4-N, TKN, P and COD were measured. This CW design provides four serial cells with synthetic liners and a river gravel base. The first two unplanted cells provide preliminary treatment. Specific gravel depths and ensuing biofilm growth provides anaerobic treatment in Cell 1 and anaerobic treatment in Cell 2. Cell 3 was planted with Typha latifolia with an inserted layer of brick rubble (for phosphorus removal). Locally grown reed, Phragmites karka was planted in Cell 4. COD was reduced from 8420 mg/l 3000 from Cell 1 to the outlet of Cell 4. Likewise other parameters: total and dissolved solids, ammonium and total nitrogen, and total P, indicated declining trends at the 4-celled CW effluent. This study reveals how high strength distillery wastewater strongly impacts morphology, aeration anatomy in the chiseled plant tissues, reed growth; and composition of the biofilm in the specialized substratum. The reliability of a CW for organic and nutrients reduction, in association with a poorly performing conventional system is discussed. There is an immense potential for appropriately designed constructed wetlands to improve high strength wastewaters in India.

The chaperone protein BiP binds to a mutant prion protein and mediates its degradation by the proteasome

Familial prion diseases are thought to result from a change in structure of the mutant prion protein (PrP), which takes a pathogenic conformation. We have examined the role of molecular chaperones in the folding of normal and mutant PrP Q217R (PrP(217)) in transfected neuroblastoma cells. In a previous report we showed that, although most of the PrP(217) forms escape the endoplasmic reticulum quality control system and aggregate in post-Golgi compartments, a significant proportion of PrP(217) retains the C-terminal glycosylphosphatidyl inositol signal peptide (PrP32), and does not exit the endoplasmic reticulum (Singh, N., Zanusso, G., Chen, S. G., Fujioka, H., Richardson, S., Gambetti, P., and Petersen, R. B. (1997) J. Biol. Chem. 272, 28461-28470). We have now studied the folding and turnover of PrP32 to understand the mechanism by which abnormal PrP forms cause cellular toxicity in our cell culture model and in the human brain carrying the Gerstmann-Sträussler-Scheinker disease Q217R mutation. In this report, we show that PrP32 remains associated with the chaperone BiP for an abnormally prolonged period of time and is degraded by the proteasomal pathway. This study is the first demonstration that BiP is chaperoning the folding of PrP and plays a role in maintaining the quality control in the PrP maturation pathway. Our data provide new insight into the diverse pathways of mutant PrP metabolism and neurotoxicity.