Genetic counselling and risk assessment
Genetic counselling helps families understand a diagnosis, the risk to relatives and their options; risks come from inheritance, probability or experience.
Key facts
- Genetic counselling gives information and support so people can make their own decisions; it is non-directive and starts before testing, not only after a result.
- A clinical genetics evaluation combines the personal and three-generation family history, a careful examination for dysmorphic features with measurements and photographs, and targeted testing.
- Mendelian recurrence risks: autosomal dominant, 50 % for every child of a parent who has the disorder; autosomal recessive, 25 % for each child of two carriers; X-linked recessive, 50 % of a carrier mother's sons are affected and 50 % of her daughters are carriers.
- For an unaffected sibling of a person with a recessive disease, the carrier probability is 2/3, since the affected genotype has been ruled out.
- For multifactorial disorders, risks are empirical: taken from what has been observed in many families, not from a model.
In detail
- Bayesian (conditional) risk combines the prior probability from the pedigree with observed information, such as a woman's several healthy sons, to give a revised (posterior) carrier risk.
- Risk is best communicated as absolute numbers and natural frequencies («1 in 4 pregnancies») rather than relative risks or percentages alone; people perceive the same number differently.
- Recurrence risk for an apparently new dominant mutation is low but not zero, because of germline mosaicism.
- Reproductive options for a couple at risk: accepting the risk, prenatal diagnosis, preimplantation genetic testing with IVF, donated gametes, adopting, or deciding not to have children.
- Genomic medicine adds new counselling tasks: uncertain variants, secondary findings and implications for relatives.
- Also called
- Recurrence risk and Bayesian risk, Clinical genetics evaluation
Clinical notes
- Cascade testing offers testing to at-risk relatives after a pathogenic variant has been identified (familial hypercholesterolaemia, Lynch syndrome, BRCA).
- Predictive testing for an untreatable adult-onset disease such as Huntington disease follows a protocol with counselling before and after the result.
Test yourself
Think of the answer, then tap the question to see it.
What is the carrier risk of the healthy sibling of a child with cystic fibrosis?
2/3: of the three possible genotypes in an unaffected child of two carriers, two are carriers.
What does a Bayesian risk calculation add?
It updates the prior risk from the pedigree with conditional information, such as the number of healthy sons, to give a posterior risk.
Which four reproductive options can a couple with a 25 % risk of a severe recessive disease consider?
Prenatal diagnosis, preimplantation genetic testing, donated gametes and adoption (or accepting the risk).
Connections
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Genetic Counseling (National Human Genome Research Institute (NHGRI), 2026); Genetic Consultation: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); If a genetic disorder runs in my family, what are the chances that my children will have the condition?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); What do the results of genetic tests mean?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.