Genetic carrier screening
Genetic carrier screening has emerged as an indispensable tool within the realm of reproductive health.
Genetic carrier screening has emerged as an indispensable tool within the realm of reproductive health, equipping medical practitioners in Australia to provide invaluable information and counsel to prospective parents. This proactive approach aims to identify individuals harboring gene mutations associated with inherited genetic disorders. Physicians commonly recommend these screenings to individuals or couples contemplating family planning, particularly before conception or during early pregnancy. The primary objective is to assess the risk of transmitting recessive genetic conditions, such as cystic fibrosis and fragile X syndrome, to their children.
When an embryo is conceived, whether through natural reproduction or assisted reproductive techniques, it inherits two copies of each gene – one from the sperm and one form the egg. Recessive genetic disorders require the inheritance of two abnormal copies, one from each parent, to manifest clinically. If only one affected gene is inherited, the individual becomes a carrier but does not manifest the condition. Importantly, parents who carry these affected genes typically do not exhibit symptoms themselves and may remain unaware of their carrier status. Given the severe clinical implications of many screened conditions, prospective parents may opt to avoid having affected offspring.
Notably, this screening is conducted on the prospective parents, not the developing fetus. The results facilitate decision-making processes, including whether couples should opt for assisted reproduction techniques, such as preimplantation genetic testing, or undergo diagnostic tests during pregnancy, which may carry certain risks, such as chorionic villus sampling.
The standard genetic carrier screening panel in Australia encompasses three pivotal tests.
Spinal Muscular Atrophy is a rare genetic disorder affecting motor neurons in the spinal cord. Individuals wi often manifest severe symptoms, including muscle weakness significantly impairing mobility, eating, and breathing.
Cystic Fibrosis (CF) is a genetic disorder with repercussions on the respiratory, digestive, and reproductive systems. Notably, one in 25 individuals carries a defective CF gene.
Fragile X Syndrome syndrome impacts cognitive development and behavior, and it can also influence the fertility of affected individuals.
Commencing from November 1, 2023, Medicare in Australia will offer a rebate for genetic carrier screening. This rebate can be applied to cover the cost of the three-test panel or towards expenses for broader screening panels encompassing hundreds of genes. It is imperative to grasp that broader screenings may result in a higher proportion of individuals testing positive as carriers for at least one condition, underscoring the comprehensive nature of these panels. The choice ultimately hinges on individual preferences and the desire for a more in-depth risk assessment. Testing can be performed sequentially, where one partner is tested and a positive result prompts testing of the other partner or both are tested simultaneously reducing any wait time for a second result.
A critical distinction exists between genetic carrier screening and Non-Invasive Prenatal Testing (NIPT). GCS identifies risk to all offspring from the same parental pairing for heritable conditions. NIPT is performed in pregnancy usually between 10-13 weeks and analyses fetal DNA in the maternal bloodstream. This tests for whole chromosome disorders (such as Down Syndrome) specific to that pregnancy. NIPT is a screening tool and requires confirmation by diagnostic tests such as amniocentesis when a positive result is returned.
Genetic carrier screening serves as an invaluable instrument for medical practitioners in Australia, enabling prospective parents to assess their risk of transmitting recessive genetic conditions, including SMA, CF, and Fragile X, to their offspring. The choice between targeted tests and comprehensive panels should be contingent upon factors such as familial history, ethnic background, and individual preferences. While NIPT is integral to prenatal care, it serves a distinct purpose by focusing on chromosomal abnormalities in the context of a specific pregnancy. The forthcoming Medicare rebate support equips medical practitioners with additional resources to guide patients towards informed decisions concerning reproductive health and family planning, thereby contributing to the well-being of future generations.
Written by Dr Sylvia Ross
FRANZCOG, MbChB, BBiomedSci, DipOMG, RANZCOG CREI Accredited Senior Fellow
Dr Sylvia Ross is a dedicated medical professional with over a decade of experience in the field of women's health. Specializing in infertility treatment, Sylvia offers a range of services to support individuals and couples facing fertility issues.