Preliminary evidence for anticipation in genetic E200K Creutzfeldt-Jakob disease

The natural history study of preclinical genetic Creutzfeldt-Jakob Disease (CJD): a prospective longitudinal study protocol

BACKGROUND

Creutzfeldt-Jakob Disease (CJD) is the most common prion disease in humans causing a rapidly progressive neurological decline and dementia and is invariably fatal. The familial forms (genetic CJD, gCJD) are caused by mutations in the PRNP gene encoding for the prion protein (PrP). In Israel, there is a large cluster of gCJD cases, carriers of an E200K mutation in the PRNP gene, and therefore the largest population of at-risk individuals in the world. The mutation is not necessarily sufficient for the formation and accumulation of the pathological prion protein (PrP^sc), suggesting that other, genetic and non-genetic factors affect the age at symptoms onset. Here we present the protocol of a cross-sectional and longitudinal natural history study of gCJD patients and first-degree relatives of gCJD patients, aiming to identify biological markers of preclinical CJD and risk factors for phenoconversion.

METHODS

The study has two groups: Patients diagnosed with gCJD, and first-degree healthy relatives (HR) (both carriers and non-carriers of the E200K mutation in the PRNP gene) of patients diagnosed with gCJD. At baseline, and at the end of every year, healthy participants are invited for an "in-depth" visit, which includes a clinical evaluation, blood and urine collection, gait assessment, brain MRI, lumbar puncture (LP), and Polysomnography (PSG). At 6 months from baseline, and then halfway through each year, participants are invited for a "brief" visit, which includes a clinical evaluation, short cognitive assessment, and blood and urine collection. gCJD patients will be invited for one "in-depth" visit, similar to the baseline visit of healthy relatives.

DISCUSSION

This continuous follow-up of the participants and the frequent assessments will allow early identification and diagnosis in case of conversion into disease. The knowledge generated from this study is likely to advance the understanding of the underlying clinicopathological processes that occur at the very beginning of CJD, as well as potential genetic and environmental risk factors for the development of the disease, therefore advancing the development of safe and efficient interventions.

TRIAL REGISTRATION

The study is an observational study. It has registered retrospectively in https://clinicaltrials.gov/ and has been assigned an identification number NCT05746715.

Pseudo-anticipation in Creutzfeldt-Jakob disease is due to a rhomboid-shaped artifact

BACKGROUND AND PURPOSE

Previous studies have reported conflicting results regarding possible anticipation in familial E200K Creutzfeldt-Jakob disease (fCJD). Our objective was to use a large database to assess the age of disease onset (AODO) in CJD.

METHODS

The study population included 477 CJD patients [266 with fCJD, 145 with sporadic CJD (sCJD) and 66 patients of Libyan origin but negative family history] from the Israeli registry of CJD conducted since 1954. In all patients, AODO in relatives and family trees was documented. Comparison of AODO was done using a paired t test and regression using Pearson correlation for birth and year of onset.

RESULTS

The initial analysis in 52/73 families in which more than one generation was affected revealed an AODO of 63.30 ± 9.44 in the first generation compared to 56.96 ± 8.99 in the second generation (P < 0.001). However, inspection of individual AODO values plotted by year of birth showed a clear rhomboid methodological artifact generated by missing data of many young onset CJD patients who died before the database began to function in 1954 and of many late onset CJD patients missing at the present time since they will only develop the disease in the future. The 'generation' effect completely disappears if analysis is performed by year of disease onset or for the periods in which complete data are available.

CONCLUSIONS

In this very large dataset, true anticipation in fCJD patients was not detected. It is plausible that previous reports supporting the presence of anticipation are biased by a rhomboid-shaped data availability artifact.

Genetic Factors in Mammalian Prion Diseases

Mammalian prion diseases are a group of neurodegenerative conditions caused by infection of the central nervous system with proteinaceous agents called prions, including sporadic, variant, and iatrogenic Creutzfeldt-Jakob disease; kuru; inherited prion disease; sheep scrapie; bovine spongiform encephalopathy; and chronic wasting disease. Prions are composed of misfolded and multimeric forms of the normal cellular prion protein (PrP). Prion diseases require host expression of the prion protein gene (PRNP) and a range of other cellular functions to support their propagation and toxicity. Inherited forms of prion disease are caused by mutation of PRNP, whereas acquired and sporadically occurring mammalian prion diseases are controlled by powerful genetic risk and modifying factors. Whereas some PrP amino acid variants cause the disease, others confer protection, dramatically altered incubation times, or changes in the clinical phenotype. Multiple mechanisms, including interference with homotypic protein interactions and the selection of the permissible prion strains in a host, play a role. Several non-PRNP factors have now been uncovered that provide insights into pathways of disease susceptibility or neurotoxicity.

Genetic PrP Prion Diseases

Genetic prion diseases (gPrDs) caused by mutations in the prion protein gene (PRNP) have been classified as genetic Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, or fatal familial insomnia. Mutations in PRNP can be missense, nonsense, and/or octapeptide repeat insertions or, possibly, deletions. These mutations can produce diverse clinical features. They may also show varying ancillary testing results and neuropathological findings. Although the majority of gPrDs have a rapid progression with a short survival time of a few months, many also present as ataxic or parkinsonian disorders, which have a slower decline over a few to several years. A few very rare mutations manifest as neuropsychiatric disorders, with systemic symptoms that include gastrointestinal disorders and neuropathy; these forms can progress over years to decades. In this review, we classify gPrDs as rapid, slow, or mixed types based on their typical rate of progression and duration, and we review the broad spectrum of phenotypes manifested by these diseases.

Familial multiple sclerosis and association with other autoimmune diseases

OBJECTIVES

Autoimmune diseases (AID) follow a complex, probably polygenic, pattern of inheritance and often cluster in families of patients with multiple sclerosis (MS). Our objective was to analyze family patterns and characteristics in families including more than one patient with MS.

MATERIALS AND METHODS

We analyzed personal and family history of neurological, systemic, and autoimmune diseases in 84 MS patients from 40 different families. Families were classified in two groups: families with cases of MS in at least two different generations (15 families) and families in which cases of MS belonged to only one generation (25 families).

RESULTS

The two previously established groups presented different clinical patterns and frequency of association with another AID. In one group, the second generation displayed a higher annual relapse rate than the first generation, higher frequency of progressive forms of MS, and more patients with another AID in addition to MS. Relapsing-remitting forms of MS (RRMS) were more frequent in the other group.

CONCLUSIONS

Families that include more than one MS patient may show two distinct patterns. This finding seems important for the compression and analysis of genetic information on MS.

LMNA-associated partial lipodystrophy: anticipation of metabolic complications

Background

Type-2 familial partial lipodystrophy (FPLD2) is a rare autosomal dominant lipodystrophic disorder due to mutations inLMNAencoding lamin A/C, a key epigenetic regulator. FPLD2 severity is determined by the occurrence of metabolic complications, especially diabetes and hypertriglyceridaemia. We evaluated the disease history and severity over generations.

Methods

This retrospective study of the largest cohort of patients with FPLD2 reported to date investigates 85 patients from 24 families comprising three generations (G1: n=39; G2: n=41; G3: n=5).

Results

Lipodystrophy appears with the same characteristics and at the same age in first generation (G1;18.6±1.5 years) and second generation (G2;15.9±0.8 years). Despite similar body mass index (23.7±0.6 vs 23.8±0.6 kg/m2), the mean delay between the onset of lipodystrophy and diabetes was far shorter in G2 (10.5±2.4 years) than in G1 (29.0±3.5 years) (p=0.0002). The same is true for the delay preceding hypertriglyceridaemia (G2: 4.5±1.4; G1: 19.3±3.2 years) (p=0.002), revealing an anticipation phenomenon. Observations in G3, and analysis within each family of disease history and diagnostic procedures, confirmed this result.

Conclusions

This study is a rare example of anticipation unrelated to a trinucleotide expansion. Discovery of this early occurrence of metabolic complications in young generations underlines the utility of presymptomatic genetic diagnosis, with careful metabolic screening and preventive lifestyle in all at-risk individuals.

Genetic prion disease: Experience of a rapidly progressive dementia center in the United States and a review of the literature

Although prion diseases are generally thought to present as rapidly progressive dementias with survival of only a few months, the phenotypic spectrum for genetic prion diseases (gPrDs) is much broader. The majority have a rapid decline with short survival, but many patients with gPrDs present as slowly progressive ataxic or parkinsonian disorders with progression over a few to several years. A few very rare mutations even present as neuropsychiatric disorders, sometimes with systemic symptoms such as gastrointestinal disorders and neuropathy, progressing over years to decades. gPrDs are caused by mutations in the prion protein gene (PRNP), and have been historically classified based on their clinicopathological features as genetic Jakob-Creutzfeldt disease (gJCD), Gerstmann-Sträussler-Scheinker (GSS), or Fatal Familial Insomnia (FFI). Mutations in PRNP can be missense, nonsense, and octapeptide repeat insertions or a deletion, and present with diverse clinical features, sensitivities of ancillary testing, and neuropathological findings. We present the UCSF gPrD cohort, including 129 symptomatic patients referred to and/or seen at UCSF between 2001 and 2016, and compare the clinical features of the gPrDs from 22 mutations identified in our cohort with data from the literature, as well as perform a literature review on most other mutations not represented in our cohort. E200K is the most common mutation worldwide, is associated with gJCD, and was the most common in the UCSF cohort. Among the GSS-associated mutations, P102L is the most commonly reported and was also the most common at UCSF. We also had several octapeptide repeat insertions (OPRI), a rare nonsense mutation (Q160X), and three novel mutations (K194E, E200G, and A224V) in our UCSF cohort. © 2016 Wiley Periodicals, Inc.

Ascertainment bias causes false signal of anticipation in genetic prion disease

Anticipation is the phenomenon whereby age of onset in genetic disease decreases in successive generations. Three independent reports have claimed anticipation in Creutzfeldt-Jakob disease (CJD) caused by the c.598G > A mutation in PRNP encoding a p.Glu200Lys (E200K) substitution in the prion protein. If confirmed, this finding would carry clear implications for genetic counseling. We analyzed pedigrees with this mutation from four prion centers worldwide (n = 217 individuals with the mutation) to analyze age of onset and death in affected and censored individuals. We show through simulation that selective ascertainment of individuals whose onset falls within the historical window since the mutation's 1989 discovery is sufficient to create robust false signals both of anticipation and of heritability of age of onset. In our data set, the number of years of anticipation observed depends upon how strictly the data are limited by the ascertainment window. Among individuals whose disease was directly observed at a study center, a 28-year difference between parent and child age of onset is observed (p = 0.002), but including individuals ascertained retrospectively through family history reduces this figure to 7 years (p = 0.005). Applying survival analysis to the most thoroughly ascertained subset of data eliminates the signal of anticipation. Moreover, even non-CJD deaths exhibit 16 years anticipation (p = 0.002), indicating that ascertainment bias can entirely explain observed anticipation. We suggest that reports of anticipation in genetic prion disease are driven entirely by ascertainment bias. Guidelines for future studies claiming statistical evidence for anticipation are suggested.

Genotype-phenotype analysis in inherited prion disease with eight octapeptide repeat insertional mutation

A minority of inherited prion diseases (IPD) are caused by four to 12 extra octapeptide repeat insertions (OPRI) in the prion protein gene (PRNP). Only four families affected by IPD with 8-OPRI have been reported, one of them was a three-generation Swedish kindred in which four of seven affected subjects had chorea which was initially attributed to Huntington's disease (HD). Following the exclusion of HD, this phenotype was labeled Huntington disease-like 1 (HDL1). Here, we provide an update on the Swedish 8-OPRI family, describe the clinical features of one of its affected members with video-recordings, compare the four 8-OPRI families and study the effect of PRNP polymorphic codon 129 and gender on phenotype. Surprisingly, the Swedish kindred displayed the longest survival of all of the 8-OPRI families with a mean of 15.1 years from onset of symptoms. Subjects with PRNP polymorphic codon 129M in the mutated allele had significantly earlier age of onset, longer survival and earlier age of death than 129V subjects. Homozygous 129MM had earlier age of onset than 129VV. Females had a significantly earlier age of onset and earlier age of death than males. Up to 50% of variability in age of onset was conferred by the combined effect of PRNP polymorphic codon 129 and gender. An inverse correlation between early age of onset and long survival was found for this mutation.

Age at Death of Creutzfeldt-Jakob disease in subsequent family generation carrying the E200K mutation of the prion protein gene

BACKGROUND

The E200K mutation of the prion protein gene (PRNP) is the most frequent amino acid substitution in genetic Creutzfeldt-Jakob disease and is the only one responsible for the appearance of clustered cases in the world. In the Israel and Slovakian clusters, age of disease onset was reduced in successive generations but the absence of a clear molecular basis raised the possibility that this event was an observational bias. The aim of the present study was to investigate possible selection biases or confounding factors related to anticipation in E200K CJD patients belonging to a cluster in Southern Italy.

METHODS

Clinical and demographical data of 41 parent-offspring pairs from 19 pedigrees of the Italian cluster of E200K patients were collected. Age at death of parents was compared with age at death of E200K CJD offspring. Subgroup analyses were performed for controlling possible selection biases, confounding factors, or both.

RESULTS

The mean age at death/last follow-up of the parent generation was 71.4 years while that of CJD offspring was 59.3 years with an estimated anticipation of 12.1 years. When the same analysis was performed including only parents with CJD or carrying the E200K mutation (n = 26), the difference between offspring and parents increased to 14.8 years.

CONCLUSIONS

These results show that early age at death occurs in offspring of families carrying the E200K PRNP mutation and that this event is not linked to observational biases. Although molecular or environmental bases for this occurrence remain unsettled, this information is important for improving the accuracy of information to give to mutated carriers.

Cerebrospinal fluid biomarkers in human genetic transmissible spongiform encephalopathies

The 14-3-3 protein test has been shown to support the clinical diagnosis of sporadic Creutzfeldt-Jakob disease (CJD) when associated with an adequate clinical context, and a high differential potential for the diagnosis of sporadic CJD has been attributed to other cerebrospinal fluid (CSF) proteins such as tau protein, S100b and neuron specific enolase (NSE). So far there has been only limited information available about biochemical markers in genetic transmissible spongiform encephalopathies (gTSE), although they represent 10–15% of human TSEs. In this study, we analyzed CSF of 174 patients with gTSEs for 14-3-3 (n = 166), tau protein (n = 78), S100b (n = 46) and NSE (n = 50). Levels of brain-derived proteins in CSF varied in different forms of gTSE. Biomarkers were found positive in the majority of gCJD (81%) and insert gTSE (69%), while they were negative in most cases of fatal familial insomnia (13%) and Gerstmann-Sträussler-Scheinker syndrome (10%). Disease duration and codon 129 genotype influence the findings in a different way than in sporadic CJD.