Genetic Testing in Prion Disease: Psychological Consequences of the Decisions to Know or Not to Know

Genetic aspects of human prion diseases

Human prion diseases are rapidly progressive and fatal neurodegenerative conditions caused by a disease-causing isoform of the native prion protein. The prion protein gene (PRNP) encodes for the cellular prion protein, which is the biological substrate for prion disease transmission and neurotoxicity. Human prion diseases have three etiologies: sporadic, genetic, and acquired. PRNP polymorphisms and pathogenic variants play a large role in the frequency, age at onset, and clinicopathologic phenotype of prion diseases. Genetic prion diseases will be covered in detail and information necessary for clinical care, predictive genetic testing, and genetic counseling will be reviewed. Because the prion protein is necessary for transmission and neurotoxicity, many experimental treatments targeting its production are being investigated and hold potential promise as a disease modifying treatment for all forms of prion disease, including asymptomatic mutation carriers. This article will review genetic aspects of human prion disease and their influence on epidemiology, clinicopathologic phenotype, diagnostics, clinical management, and potential treatment approaches.

Genetic counseling for prion disease: Updates and best practices

Prion disease is a rare, fatal, and often rapidly progressive neurodegenerative disease. Ten to fifteen percent of cases are caused by autosomal dominant gain-of-function variants in the prion protein gene, PRNP. Rarity and phenotypic variability complicate diagnosis, often obscuring family history and leaving families unprepared for the genetic implications of an index case. Several recent developments inspire this update in best practices for prion disease genetic counseling. A new prion-detection assay has transformed symptomatic diagnosis. Meanwhile, penetrance, age of onset, and duration of illness have been systematically characterized across PRNP variants in a global cohort. Clinically, the traditional genotype-phenotype correlation has weakened over time, and the term genetic prion disease may now better serve providers than the historical subtypes Creutzfeldt-Jakob disease, fatal familial insomnia, and Gerstmann-Sträussler-Scheinker disease. Finally, in the age of genetically targeted therapies, clinical trials for prion disease are being envisaged, and healthy at-risk individuals may be best positioned to benefit. Such individuals need to be able to access clinical services for genetic counseling and testing. Thus, this update on the genetics of prion disease and best practices for genetic counseling for this disease aims to provide the information needed to expand genetic counseling services.

Identifying medical mimics for late-life mania: A case of prion disease

Sporadic Creutzfeld Jakob Disease is a rare disease with diagnostic challenges. While there is very little human data regarding this disease, some studies have indicated that certain medications may be useful in slowing its progression. Case study data implies psychiatric and cognitive symptoms preceding the diagnosis. This single case report presents a 68-year-old male with suspected late-onset bipolar disorder, later found to have sporadic Creutzfeld Jakob Disease. The patient was treated with lithium for this purported bipolar disorder. Approximately 2 years later, the patient met the Center for Disease Control (CDC) diagnostic criteria for prion disease following a rapid decline in cognition. This case provides an example of a medical mimic of bipolar disorder in the geriatric population.

Plasma neurofilament light chain as a biomarker for Fatal Familial Insomnia

BACKGROUND

Fatal Familial Insomnia is a rare hereditary prion disease associated with the D178N-129M PRNP mutation. Early diagnosis is difficult because the clinical syndrome may overlap with affective disorders. In addition, most known cerebrospinal fluid biomarkers for prion diseases and magnetic resonance imaging do not show a good diagnostic accuracy for Fatal Familial Insomnia. In this context, data on plasma biomarkers are scarce.

METHODS

We analyzed levels of neurofilament light chain, glial fibrillary acidic protein, chitinase-3-like protein 1, calcium-binding protein B, and total Tau protein in six serial plasma samples from a patient with Fatal Familial Insomnia. Subsequently, plasma neurofilament light chain was analyzed in n=25 patients and n=19 controls. The diagnostic accuracy and associations with disease stage and duration were explored.

RESULTS

Among all biomarker candidates in the case study, only neurofilament light chain levels showed a constant evolution and increased over time. It discriminated Fatal Familial Insomnia from controls with an area under the curve of 0.992 (95%CI:0.974 to 1) in the case-control study. Higher concentrations were associated with methionine homozygosity at Codon 129 PRNP (p=0.006), shorter total disease duration (rho=-0.467, p=0.019, 95%CI:-0.790 to -0.015), and shorter time from sampling to death (rho=-0.467, p=0.019, 95%CI -0.773 to -0.019).

CONCLUSION

Plasma neurofilament light chain may be a valuable minimal-invasive diagnostic biomarker for Fatal Familial Insomnia after clinical onset. Most important, stage-related increase and association with disease duration indicate potential as a prognostic marker and as a surrogate marker in clinical trials.

Genetic counseling and testing practices for late-onset neurodegenerative disease: a systematic review

Objective

To understand contemporary genetic counseling and testing practices for late-onset neurodegenerative diseases (LONDs), and identify whether practices address the internationally accepted goals of genetic counseling: interpretation, counseling, education, and support.

Methods

Four databases were systematically searched for articles published from 2009 to 2020. Peer-reviewed research articles in English that reported research and clinical genetic counseling and testing practices for LONDs were included. A narrative synthesis was conducted to describe different practices and map genetic counseling activities to the goals. Risk of bias was assessed using the Qualsyst tool. The protocol was registered with PROSPERO (CRD42019121421).

Results

Sixty-one studies from 68 papers were included. Most papers focused on predictive testing (58/68) and Huntington’s disease (41/68). There was variation between papers in study design, study population, outcomes, interventions, and settings. Although there were commonalities, novel and inconsistent genetic counseling practices were identified. Eighteen papers addressed all four goals of genetic counseling.

Conclusion

Contemporary genetic counseling and testing practices for LONDs are varied and informed by regional differences and the presence of different health providers. A flexible, multidisciplinary, client- and family-centered care continues to emerge. As genetic testing becomes a routine part of care for patients (and their relatives), health providers must balance their limited time and resources with ensuring clients are safely and effectively counseled, and all four genetic counseling goals are addressed. Areas of further research include diagnostic and reproductive genetic counseling/testing practices, evaluations of novel approaches to care, and the role and use of different health providers in practice.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-021-10461-5.

Who and Why? Requests for Presymptomatic Genetic Testing for Amyotrophic Lateral Sclerosis/Frontotemporal Dementia vs Huntington Disease

Objective

We aimed to describe the population of subjects seeking presymptomatic counseling for amyotrophic lateral sclerosis and/or frontotemporal dementia (ALS/FTD) and compared them with those demanding the well-established presymptomatic test for Huntington disease (HD).

Methods

We retrospectively examined the requests of a cohort of individuals at risk of familial ALS/FTD and 1 at risk of HD over the same time frame of 11 years. The individuals were seen in the referral center of our neurogenetics unit.

Results

Of the 106 presymptomatic testing (PT) requests from subjects at risk of ALS/FTD, 65% were seen in the last 3 years. Over two-thirds of the subjects were at risk of carrying mutations responsible for ALS, FTD, or both. Sixty-two percent of the subjects came from families with a known hexanucleotide repeat expansion in C9ORF72. During the same period, we counseled 840 subjects at risk of HD. Subjects at risk of ALS/FTD had the presymptomatic test significantly sooner after being aware of their risk, but were older than those at risk of HD. The youngest subjects requesting the test had the highest disease load in the family (p < 0.05).

Conclusions

Demands for PT for ALS/FTD have been increasingly growing, particularly since the discovery of the C9ORF72 gene. The major specificity of the genetic counseling for these diseases is the unpredictability of the clinical phenotype for most of the genes involved. Awareness of this added uncertainty does not prevent individuals from taking the test, as the dropout rate is not higher than that for HD.

Informing about genetic risk in families with Huntington disease: comparison of attitudes across two decades

The low uptake of presymptomatic testing in Huntington disease prompted us to question family members on how they handle the transmission of information regarding genetic risk. We hypothesised that in 2019, parents would inform their at-risk children about their genetic risk more and at a younger age than in 2000, given the availability of prenatal diagnosis, French legislation changes since 2011, and recent therapeutic advances. We made a questionnaire available about the transmission of genetic information within families with Huntington disease in 2000 and 2019. We obtained 443 questionnaires (295 in 2019 and 148 in 2000). Participants were mainly at-risk for Huntington disease (n = 113), affected (n = 85), and spouses (n = 154). In 2019, participants had a higher mean education level (p < 0.01) and a mean age of 44.1 ± 15.1 years (vs 48.1 ± 11.4 years in 2000, p < 0.01). They had been informed about the risk of being a carrier at around 30 years of age (29.0 ± 14.2 in 2019 vs 32.2 ± 13.8 in 2000, p = 0.09). However, they would inform at an earlier age (≤18 years, 67% vs 59%, p = 0.16). Information on transmission risk had been given primarily by parents (45% vs 30%, p = 0.06). In addition, genetic testing for relatives unaware of their status was recommended more frequently in 2019 (46% vs 32%, p < 0.001). Respondents in 2019 recommended genetic testing more often but overall attitudes towards information and testing have not changed significantly over the 19-year time period since the questionnaire was first delivered even despite recent clinical trials potential disease modifying therapies.

Rare genetic E196A mutation in a patient with Creutzfeldt-Jakob disease: a case report and literature

Genetic Creutzfeldt–Jakob disease (gCJD) is characterized by mutations in the PRNP gene and represents approximately 10–15% of the human prion diseases. Here, we report a 42-year-old Chinese man who was diagnosed with gCJD. The patient had a rare mutation in codon 196 (E196A) of PRNP leading to an exchange of amino acid from glutamic acid (E) to alanine (A). The polymorphism of codon 129 in the patient was methionine homozygote. His mother and daughter are asymptomatic carriers of the same mutation. The clinical manifestations were similar to those of sporadic CJD. 14-3-3 protein was positive in cerebrospinal fluid, and there were sharp slow complex waves in electroencephalography and ribbon-like signals on magnetic resonance imaging (MRI). The main complaints of patient changed from visual space and visual colour to psychotic symptoms with enhanced high signal intensity on the occipital and frontal cortices on MRI. We compared the clinical characteristics of the current patient with those of previously reported Chinese patients with other gCJD of E196A mutation to summarize the common features of E196A gCJD.