New position statements from the RACGP and RANZCOG recognise the importance of preconception carrier screening. Patients may present to general practice looking for information regarding rare genetic conditions and the role of genetic testing.
What is preconception carrier screening?
Preconception carrier screening is genetic testing performed ideally prior to pregnancy, to assist couples in identifying their own chance of having a child with a clinically serious genetic condition. Couples will generally not have a family history of a genetic condition as the conditions tested are recessive conditions in which carriers mostly do not have symptoms; for couples who do, a referral to a genetic counsellor for targeted genetic testing is advised.
There are numerous preconception carrier screening options currently available in the market. The first group is a panel of three of the more common genetic conditions including Fragile X syndrome, Cystic Fibrosis and Spinal Muscular Atrophy (SMA). While the second group is an expanded panel including any number of genes from a hundred or so to over three hundred disorders.
Benefits for your patients
While individuals of certain ethnic backgrounds may have a higher likelihood of carrying particular conditions, the global nature of our population makes it difficult to determine those couples at a higher risk based on ethnicity alone. Therefore all individuals of child bearing age should be offered the opportunity to consider preconception screening. This gives couples the opportunity to discuss preconception carrier screening, and assist them in making an informed decision around their own reproductive health.
It is important that couples have access to genetic counselling before undergoing preconception carrier screening, rather than only offering post-test counselling to those with a positive carrier result. The benefits and limitations of the test, it’s cost and timeline to a result can all be discussed in pre-test genetic counselling. Most critically though is helping the couple to determine how they will incorporate the results into their family planning.
Identifying their chance of a serious genetic condition provides the opportunity for preimplantation genetic diagnosis using IVF, prenatal testing with chorionic villus sampling or amniocentesis and in some cases such as SMA type 1, identifies those babies who might benefit from very early therapies. Couples who receive a positive result in the absence of pre-test counselling may face unnecessary distress if they do not have the information or tools they need to understand how they might use the information within the context of their own values and family planning.
It is also important for couples to understand what preconception carrier screening does not cover. The expanded panel includes both autosomal recessive and X-linked recessive conditions.
Some panels cover haemoglobinopathies such as thalassaemia and haemophilia, whilst others do not. Pre-test genetic counselling is an opportunity for couples to learn in depth about this screen from an expert in the field. Dominant conditions are not included and a ‘no variant identified’ result does not exclude the possibility of a pregnancy with a condition not covered by the panel or occurring in the pregnancy for the first time (de novo event). It also does not include conditions that are not genetic or for which there is no test, such as autism.
There are two options for preconception carrier screening. These are sequential screening with testing the woman first, followed by partner screening if the woman is identified as a carrier or testing both partners together. Whilst the former favours a more economical approach in the short term if the woman is not identified as a carrier, the latter is preferable; the timeline will be shorter, and each partner will have the same information regarding their own individual carrier status.
General practitioners play a key role in raising awareness about preconception carrier screening. Taking a three generation family history to identify individuals who require targeted genetic testing, raising this topic with patients and offering a referral to a genetic counsellor will ensure that your patients are well informed regarding their options for preconception carrier screening.
This article was contributed by Clinical Geneticist, Dr Di Milnes BMBS (Hons) DCh GradCertBEth FRACP from Genes Australia. Visit the Genes Australia website for more information.