For counsellors

How much prion disease is genetic?

A 2022 review gives genetic prion disease as the cause of 10 to 15 percent of all cases, arising from pathogenic variants in PRNP. Four variants, E200K, D178N, P102L and A117V, account for over half of genetic cases, and E200K is the most common cause of genetic CJD worldwide.

Penetrance differs sharply between variants in the published figures, and this is the point counsellors most often have to unpick. The review describes D178N and P102L as nearly fully penetrant, V180I as very low at about 1 percent, V210I at about 10 percent, and E200K as incompletely penetrant with the probability rising with age. Phenotype can also turn on the codon 129 polymorphism on the mutated allele: D178N with methionine usually causes fatal familial insomnia, while D178N with valine usually causes a genetic CJD phenotype.

A family history is usual in genetic prion disease but is not always present. The review lists the reasons: low penetrance, relatives who were misdiagnosed, carriers who died before onset, misattributed parentage and incomplete family information. It does not give a figure for how often the history is absent.

What does the counselling process look like?

The 2022 review recommends that people undergoing predictive genetic testing receive genetic counselling before testing, following the Huntington disease protocol. That model includes pre-test neurological and psychiatric examination, with results disclosed in the presence of a support person. The review gives a specific reason for the pre-test neurological examination: some people develop symptoms shortly after receiving their result. Psychiatric screening assesses readiness and suicide risk, and the authors note the large psychological burden carried by families affected by genetic prion disease.

An Israeli expert panel published a ten-point practice framework in 2026, developed by 23 core members including neurologists, medical geneticists, genetic counsellors, a cognitive neurology nurse and a medical psychologist. Its recommendations are that asymptomatic relatives of patients with genetic CJD should be offered genetic counselling; that counselling be given by genetic health professionals or by neurologists familiar with the disease, in line with local regulations; that testing not be offered to people under 18, with careful review of motivation, emotional resilience and impulsivity in those aged roughly 18 to 25; that people in acute emotional distress, such as after a relative’s diagnosis or death, be encouraged to delay testing by at least six months; that prenatal and preimplantation testing decisions be made case by case; that pre-test psychological appraisal be used to evaluate preparedness for a positive result, with a structured assessment by a mental health professional; that testing follow four structured steps of initial counselling, psychological assessment, blood sampling and disclosure; that results be delivered in person by the same trained clinician or genetic counsellor who gave the initial counselling; that health systems develop a structured and accessible support programme for asymptomatic carriers and their families; and that carriers be offered the chance to join research.

The panel did not reach consensus on whether psychological assessment can be waived when someone declines it, noting arguments from autonomy against making it a strict prerequisite, and suggesting that exceptional cases go to a multidisciplinary team or an ethics committee. It recommends that counselling and testing be publicly funded, and reports that annual presymptomatic testing episodes at one Israeli centre rose from about two or three a year between 2014 and 2017 to 29 individuals in 2024.

The panel also rejected proactively offering testing to everyone of Libyan or Tunisian Jewish descent, on the grounds that it could stigmatise communities and cause unnecessary distress given the low absolute risk. Offering counselling to those who ask is a separate question, and the panel supported access for any relative of a person with genetic or apparently sporadic CJD who wants it.

What a result can and cannot tell someone is covered in what a genetic result can tell you, and the testing process itself in predictive testing. The variants and their published penetrance figures are in PRNP variants. Deciding not to test is a settled outcome, and not a step that has been postponed.

What about minors?

The NSGC position statement revised on 16 October 2025 generally discourages predictive genetic testing of asymptomatic minors for adult-onset conditions and predispositions, allows that testing can still be appropriate in some circumstances, and strongly recommends counselling before and after a test. The factors it names are clinical management and psychological impact, the availability of follow-up specialists, and the minor’s autonomy, age and capacity to assent or consent. It favours a narrow test scope, planning disclosure in advance with direct disclosure to the minor where appropriate, and attention to institutional, state and federal law including provisions on genetic discrimination. It notes that implications shift as knowledge of onset and treatment changes, so a decision to test or to defer may need revisiting.

The 2022 review states that genetic testing is not conducted on minors unless there is valid concern that the individual may be symptomatic, which the authors say would rarely happen. The Israeli framework sets 18 as a floor and treats testing in young adults as non-urgent, noting that genetic CJD in Israel rarely appears before the age of 40.

What reproductive options are described?

The 2022 review names adoption, prenatal testing and preimplantation genetic diagnosis with in vitro fertilisation as the routes discussed with carriers, and notes that preimplantation testing can be performed without the parent learning their own variant status. It records that prenatal testing raises moral, ethical and legal questions.

A 2014 case report described preimplantation genetic diagnosis for a family with the F198S variant using sequential polar body analysis with blastomere confirmation, and named non-disclosure preimplantation diagnosis as a protocol in which the person remains unaware of their own genotype. Its authors concluded that clinicians should discuss preimplantation diagnosis as an option with patients genetically predisposed to prion disease, and suggested that its availability may affect decisions about predictive testing.

The Israeli framework reports that preimplantation testing is publicly funded in Israel for up to two healthy offspring, that both direct testing for a known familial variant and exclusion testing are available, and that prenatal diagnosis is possible by chorionic villus sampling at about 11 to 12 weeks or amniocentesis at about 17 to 23 weeks. It places the ethics of termination outside its scope. What is available, funded and lawful differs by country, so the local service is the only reliable answer.

When a diagnosis has just happened in the family

Two practical points recur. Blood taken and stored during the acute illness keeps the genetic question answerable later: the Australian registry recommends storing blood from every suspected patient so that relatives can be tested in future, and notes that this storage is optional and that testing is voluntary. Where blood was not taken, tissue obtained at post-mortem examination may be the remaining route, and in that situation the next of kin is asked at consent whether genetic results should be disclosed, with the option to defer.

The second point is timing. Both the Israeli framework and the Huntington model place distance between a bereavement and a testing decision. Support in that period is covered in grief and bereavement, and the 2026 UK palliative care recommendations note that for inherited prion disease the National Prion Clinic can provide follow-on care for at-risk family members.

Where can a family find a counsellor?

The NSGC Find a Genetic Counselor directory gives access to over 3,300 genetic counsellors in the United States and Canada, with separate routes for counsellors who meet patients in person at a designated location and counsellors who meet by phone, video conferencing or other virtual means. NSGC describes it as a list of members and not a referral service, makes no guarantee about individual skills, and advises users to check insurance coverage. Routes elsewhere are gathered in referral routes and by country at countries.

Wording for the conversations themselves is in talking about prion disease. The clinical side of diagnosis and surveillance sits in for clinicians, and the plain-language pages families read first start at understanding prion disease.