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# 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.

Updated Nov 13, 2026

## 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).

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## Connections

## Related conditions 4

- [Duchenne muscular dystrophy](https://durgical.com/en/conditions/duchenne-muscular-dystrophy/)
- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)
- [Huntington disease](https://durgical.com/en/conditions/huntington-disease/)
- [Down syndrome (trisomy 21)](https://durgical.com/en/conditions/down-syndrome/)

## Related 5

- [Inheritance concepts, genotype–phenotype and the pedigree](https://durgical.com/en/biochemistry/topics/inheritance-concepts-genotype-phenotype-and-the-pedigree/)
- [Genetic tests: what each one finds](https://durgical.com/en/biochemistry/topics/genetic-tests-what-each-one-finds/)
- [Population genetics: Hardy–Weinberg and carrier frequency](https://durgical.com/en/biochemistry/topics/population-genetics-hardy-weinberg-and-carrier-frequency/)
- [Interpreting genetic variants: classes, evidence and databases](https://durgical.com/en/biochemistry/topics/interpreting-genetic-variants-classes-evidence-and-databases/)
- [Complex traits: familial risk, twins, heritability and polygenic scores](https://durgical.com/en/biochemistry/topics/complex-traits-familial-risk-twins-heritability-and-polygenic-scores/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Genetic Counseling](https://www.genome.gov/genetics-glossary/Genetic-Counseling) (National Human Genome Research Institute (NHGRI), 2026); [Genetic Consultation: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/consult/) (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](https://medlineplus.gov/genetics/understanding/inheritance/riskassessment/) (MedlinePlus, US National Library of Medicine, 2026); [What do the results of genetic tests mean?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/testing/interpretingresults/) (MedlinePlus, US National Library of Medicine, 2026).

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