What a genetic result means for your family

How a variant passes through a family

Most inherited conditions a genome can find follow a pattern that shows who else may carry them. A person with an autosomal dominant condition has a 50 percent chance of passing the altered gene to each child [1]. Unless the variant arose new in you, one of your parents usually carries it too, which is why brothers and sisters may also want to know [1].

For recessive conditions, two parents who each carry the same variant have a 25 percent chance with each pregnancy of an affected child [1]. A carrier result matters mostly for family planning, for you and for relatives who may have children.

Whether a relative who carries a variant ever develops the condition is a separate question. Penetrance differs widely between genes, and in large population studies it was generally low for variants found without a family history [2].

What cascade testing is

Cascade testing means offering a test to relatives, moving outward through the family, once a variant has been found in one person. For familial hypercholesterolaemia, NICE recommends DNA cascade testing of first and second degree relatives, and third degree relatives where possible, of anyone with a genetic diagnosis [3].

A relative usually needs only a targeted test for the known variant, which is quicker and gives a clearer answer because the laboratory knows exactly what to look for. A negative result in a relative can be as useful as a positive one, because both change their risk assessment [4].

Who to tell, and how

UK guidance asks doctors to discuss family communication routinely and to help you identify the relatives who need the information [4]. That usually means parents, brothers, sisters and children first, then the wider family as the picture becomes clear.

Many people find this hard, and the guidance notes that significant proportions of relatives who need the information never learn of their risk [4]. Across 87 studies of inherited cancer, 48% of relatives had genetic counselling and 41% had a test [5]. For inherited breast and ovarian cancer, a separate review of 30 studies found that 33% of relatives were tested [6].

Support from the medical team makes a difference. When it contacted relatives directly, with the patient’s agreement, uptake of counselling was 63% compared with 35% when patients passed the news on themselves [5].

A checklist for sharing a result

These steps make the conversation easier for you and more useful for the people you tell.

• Draw a family tree across three generations, with ages and any diagnoses you know of.
• Mark which side of the family the variant is likely to have come from, if that is known.
• Ask your doctor for a short letter to pass on, naming the variant and the test a relative would need.
• Decide who you will tell yourself, and where you would like help.
• Think about timing for anyone facing a pregnancy or an illness, without leaving it indefinitely.
• Keep a copy of your report, because a relative’s laboratory will need the exact variant.

Your privacy, and your relatives’ interests

Your result is confidential, and UK guidance explains that a doctor’s duty of confidentiality has limits, and that a clinician may need to weigh your confidence against a relative’s interest in knowing about a serious risk [4]. Outright refusal to share is rare, and a relative can often be alerted to a risk without your own details being disclosed [4].

Under the UK Code on Genetic Testing and Insurance, insurers will not ask anyone to disclose the predictive genetic result of another person, such as a blood relative [7]. A relative who has their own predictive test is covered by the same code, which currently lets an insurer ask only about Huntington’s disease on life cover above £500,000 [7].

Children, urgent signs and questions to ask

Children are usually tested for a family variant only when the result would change their care in childhood, for example where screening starts young [4]. Otherwise the decision is often left until they can make it themselves.

If a relative died suddenly and young, or someone in the family has fainted during exercise, raise it with a doctor soon. If anyone has chest pain, palpitations, collapses or struggles to breathe, call 999 in the UK or the local emergency number elsewhere.

• Which relatives should be offered a test, and in what order?
• What would a positive or a negative result mean for each of them?
• Can you write a letter I can share with my family?
• Does the variant matter for my children, and from what age?

How The Wellness can help

A doctor reads your genome result with you, with a genetic counsellor alongside, writes a plan into your record and helps you decide who in your family to tell. On The Vantage, relatives are screened for a family finding at a family rate, and on The Legacy that screening is included for two relatives.

If you already hold a result from elsewhere, a GP appointment is a calm place to start. Our GMC registered doctors see patients on Baker Street in Marylebone and Eccleston Street in Belgravia, and relatives abroad can be seen through partners in 12 other cities.