The chances of having a baby with 5q SMA vary depending on whether you or your partner have 5q SMA or are carriers.

If you already have a child with 5q SMA and your unborn baby also has inherited 5q SMA then it is likely, but not certain, that your unborn baby will also have the same Type of 5q SMA. This means that siblings with SMA tend to be affected in a similar way, or at a similar age. However, this is not always the case.

A genetic counsellor can discuss your individual genetic circumstances with you and give advice and information about all your testing options either before you consider any pregnancy or as early in your pregnancy as possible. If possible, genetic counselling before pregnancy will give you and your partner more time to think about genetic testing and the difficult decisions this can raise. Genetic counselling will also support you through the emotional impact of any option you choose and discuss what the next steps might be for you and your family.

If SMA has occurred in your extended family but you do not know if you are a carrier of SMA and are thinking of having children, you can ask your GP to refer you and your partner to your regional Genetics Centre for genetic testing (see below).

If you are a carrier of SMA or have SMA, you can be referred to your local Genetics Centre by a GP, specialist, midwife or obstetrician. If you are pregnant, you can ask for an urgent genetic counselling referral. If this isn’t possible, you can contact your local genetic service directly.

As a general rule, genetic testing cannot guarantee 100% accuracy, but measures are taken to try and ensure that genetic test results are as close to 100% accuracy as possible.

If you and your partner are both carriers of SMA (or one of you is a carrier and the other is affected by SMA), you may wish to consider testing a pregnancy for SMA. There are different reasons why couples may want to do this, such as preparing for the arrival of their baby or deciding to end the pregnancy.

There is a chance that a child will inherit 5q SMA if:

• both partners are carriers of SMA or
• one partner has SMA, the other is a carrier

(See The Genetics of 5q SMA > for more information about the chances that a child will inherit 5q SMA in these and other scenarios.)

There are several options which may be available to you:

• You can plan to conceive naturally and avoid any testing for SMA during a pregnancy. Your Genetic Counsellor can discuss the chances of you having a child affected by SMA and can organise testing for the baby during the newborn period, if you wish.
• You can conceive naturally and have testing during pregnancy to see if the baby will be affected by SMA. This can be done by non-invasive or invasive methods, which is discussed later.
• You can have a type of fertility treatment, called Pre-Implantation Genetic Testing for a monogenic condition (PGT-M). This means that embryos will be tested for SMA before achieving a pregnancy. Again, this is discussed later.

Conceiving naturally and testing the baby after birth

Newborn screening for SMA is not yet routine in the UK, and genetic testing for SMA at birth will not usually be offered if a child shows no symptoms and only one parent (or neither parent) is a carrier of SMA. However, if both parents are considered to be carriers of SMA, you can ask your Genetic Counsellor if your newborn baby can be tested. This is usually done by taking a cord blood sample, or a blood sample directly from the baby. Both can be done shortly after the birth of the baby and the results are usually available within 1-2 weeks, but sometimes can take longer.

If a genetic test is taken and your baby is found to have inherited SMA, the results of their test will determine whether they are eligible for one of the NHS-funded drug treatments for pre-symptomatic SMA. The criteria for eligibility are quite complicated. Again, it would be worth talking through what the treatment options would be with your genetic counsellor – or clinical team if you have one. If you aren’t in touch with a specialist SMA clinical team and your genetic counsellor is not familiar with the eligibility criteria and treatment options for SMA, they should get in touch with your nearest Treating Paediatric Neuromuscular Specialist Centre > 

This may be an option before pregnancy for couples who want to exclude the possibility of their baby having 5q SMA and / or may be having difficulty conceiving. There is often a wait for the initial consultation and then starting PGT-M may be delayed while ethical approval and / or funding is arranged. In the United Kingdom, the Human Fertilisation and Embryology Authority (HFEA) has approved the use of PGT-M for couples at risk of having a child with SMA types 1, 2 or 3. As PGT-M also involves IVF (In vitro fertilisation) and this also takes time, realistically PGT-M may take many months, or sometimes even years.

For more information about PGT-M, you can ask for a referral to your local Regional Genetics clinic to discuss this option with a genetic counsellor.

What Does IVF with PGT-M Involve?

In-vitro fertilisation (IVF) is carried out using a couple’s own eggs and sperm Eggs are removed from the woman’s ovaries and fertilised with sperm in a laboratory.

After about 5 days, once the embryos have grown into balls of cells (‘blastocysts’), a small sample of cells is very carefully removed (an embryo ‘biopsy’). After the biopsy, the embryos are rapidly frozen (vitrification) while cells are genetically tested for 5q SMA.

Once the genetic test is completed, and providing the results show that there is at least one embryo that doesn’t have SMA, this embryo can then be selected, warmed and transferred into the womb. A pregnancy test is carried out 12 days later to see whether the PGT-M treatment has been successful.

Who Can Have IVF with PGT-M?

There are eligibility criteria for both the PGT-M process and for NHS funding. These overlap, so some couples may meet one set of criteria but not the other, neither, or both. Different PGT-M centres may also have different criteria. Your genetic counsellor will explain whether you are eligible.

This is an option from around the 9th week of pregnancy for couples who wish to know whether their baby has inherited SMA. This option does not involve invasive testing and therefore there is no risk of miscarriage as a result of the test.

In order to do the test:

• Both parents must be known carriers of an SMN1 gene alteration (mutation) and
• A DNA sample must be available from either the family member affected with SMA (this may be a previous child of the couple or another affected relative) or from a previous child of the couple who has been confirmed not to be a carrier (does not have an altered copy of the SMN1 gene)

Testing can be done in single pregnancies but may not be possible in multiple pregnancies. This test is not currently possible for consanguineous (related) couples.

What is involved with NIPD?

A sample of the mother’s blood is taken from around 9 weeks gestation. This is tested for the unborn baby’s genetic material.

If a couple has had a previous child affected with SMA, it is likely that there are already stored laboratory samples from previous testing for both the father and the affected child, in which case new samples from them may not be needed.

The test result should be available within 21 days, although results are often available quicker than this.

What Will the NIPD Test Show?

The NIPD testing will show whether the foetus has inherited the affected or unaffected copy of the SMN1 gene from each parent. If the foetus has inherited one affected copy of the SMN1 gene, and one unaffected copy, then they are a carrier of 5q SMA but are very unlikely to be affected. If the foetus has inherited two affected copies of the SMN1 gene (one from each parent) then the child will have 5q SMA. However, testing cannot show the type of 5q SMA the child will have (Types 1,2 and 3 usually have childhood onset and SMA Type 4 typically has adult onset). This testing will not check for SMN2 copy number.

Very occasionally, the test may not return a result. If this happens the test may be repeated or an alternative invasive test (CVS or amniocentesis – see next sections) may be carried out.

When using NIPD, there is a small, estimated risk of misdiagnosis (approximately 1 in 500-1000) due to technical and biological reasons.

What Next?

You would be given information and support before, during and after your NIPD treatment to help you decide what to do next. Your options at this point would be to continue with the pregnancy or, depending on the stage of your pregnancy, to end the pregnancy.

How can I access this test?

Access to this testing and genetic counselling is through your local genetics centre, wherever you live in the UK. Your genetics centre will be able to advise you on funding / charges for NIPD.

This is an option from around 11 weeks of pregnancy for couples who wish to know whether their baby has SMA.

What’s Involved?

CVS involves taking a sample of the placenta and testing the cells for 5q SMA. This involves either inserting a needle through the abdomen (transabdominal CVS) or inserting a tube through the cervix (transcervical CVS). Both processes are guided by a scanner.

The sample is sent to a laboratory and genetically tested for 5q SMA. It cannot show the Type of 5q SMA, although the laboratory may also test for SMN2 copy number which can help your genetics team to predict how severe the SMA symptoms might be. It generally takes a week for the test result, but this may vary. You can ask how long it’ll take for the result and decide how you will be informed.

It is generally agreed that there is an increased risk of miscarriage associated with CVS as it is an invasive test. This risk is estimated to be up to 1 in 200 (0.5%) for single pregnancies and approximately 1 in 100 (1%) in multiple pregnancies (such as twins or triplets).

What Next?

You would be given information and support before, during and after your CVS treatment to help you decide what to do next. Your options at this point would be to continue with the pregnancy or to have a termination.

This is an option from around 15 weeks of pregnancy for couples who wish to know whether their baby has SMA.

What’s Involved?

Amniocentesis involves putting a needle through the abdomen to remove some of the fluid that surrounds the foetus in the womb (amniotic fluid).

The cells in the amniotic fluid are sent to a laboratory and genetically tested for 5q SMA. It cannot show the Type of SMA, although the laboratory may also test for SMN2 copy number which can help your genetics team to predict how severe the SMA symptoms might be. The test results are usually available in around 1-2 weeks. You can ask how long it’ll take for your result and decide how you will be informed.

It is generally agreed that there is an increased risk of miscarriage associated with amniocentesis. The risk of miscarriage is estimated to be up to 1 in 200 (0.5%) in single pregnancies and up to 1 in 100 (1%) in multiple pregnancies (such as twins and triplets).

What Next?

You would be given information and support before, during and after your amniocentesis to help you decide what to do next. Your options at this point would be to continue with the pregnancy or to have a termination. If you decide to have a termination following amniocentesis, this time difference can mean you need to have a different type of termination due to the potentially later stage of the pregnancy.

This is an option before pregnancy which may be available for couples who want to exclude the possibility of their baby having 5q SMA and / or may be having difficulty conceiving.

What does IVF involve?

During IVF, an egg is removed from a woman’s ovaries and fertilised with sperm in a laboratory. After a few days, the fertilised egg, called an embryo, is then transferred into the prospective mother’s womb. There is then a 2 week wait for a pregnancy test to see if the treatment has worked.

Depending on a couple’s circumstances, IVF would be carried out using eggs and / or sperm from donors who have been tested to check that they are not carriers of 5q SMA.

Your genetic counsellor will be able to discuss whether this could be an option for you.

Antenatal Results and Choices (ARC)

ARC is a national charity helping parents and healthcare professionals through antenatal screening and its consequences. They offer non-directive information and support to parents: before, during and after antenatal screening; if their baby has a diagnosis; if they are making difficult decisions about continuing with or ending a pregnancy; if they are coping with complex and painful issues after making a decision, including bereavement.

ARC’s helpline is available Monday to Friday 10.00am to 5.30pm, 0845 077 2290 from a landline and 0207 713 7486 from a mobile. Visit ARC’s website >.

Miscarriage Association

Information and support for anyone affected by miscarriage.
Helpline: 01924 200 799 Monday to Friday 9am-4pm. Visit Miscarriage Association’s website >.

SMA UK

SMA UK provides free, confidential information and support to anyone affected by SMA. We do not offer a counselling service and aren’t experts in terms of family planning options but we’re always willing to listen and offer emotional support. Phone: 01789 267520 or contact our Support Team >.