![]() High school screening has been offered in particular to the Ashkenazi Jewish community. Reproductive carrier screening has been offered in a number of settings. 5 There are a number of companies in Australia and internationally offering expanded carrier screening for over 100 genetic conditions. This form of screening is called expanded carrier screening and is now widely available. The advent of massively parallel sequencing has meant that it does not cost much more to screen for hundreds or thousands of conditions than it does to screen for a few. In recent years it has become possible to ascertain the DNA sequence of many genes at once (massively parallel sequencing, also called next generation sequencing) and therefore identify carriers not only of common mutations, but also of rare mutations. 8 This was initially by targeted testing for common CFTR mutations. The first disorder for which widespread screening became available by genetic testing was CF. Once mutations in genes were identified as the cause of genetic disorders, screening for an ever-increasing number of disorders became possible. Screening programs for these disorders were therefore established in high-risk communities. Carrier screening for these conditions was possible because carriers have blood parameters that differ from non-carriers (ie abnormalities on haemoglobin electrophoresis for haemoglobinopathies and lower levels of the enzyme hexosaminidase A for TSD). In the 1970s, prior to the first gene being cloned, it became possible to screen for carrier status for two conditions: haemoglobinopathies such as beta-thalassaemia and sickle cell disease, 6 and TSD 7. For some X-linked conditions (such as fragile X syndrome), females who carry a mutation may display some features of the condition. 5 Carriers can be identified by genetic testing, and at-risk individuals and couples have the option to take steps to avoid having affected children.įigure 1. The aim of genetic carrier screening is ‘to facilitate informed reproductive decision making by identifying those couples at risk of having an affected child’. 3 The risk is considerably higher for consanguineous couples. Approximately 1–2% of non-consanguineous couples have a one in four chance of having a child with an autosomal recessive or X-linked recessive condition. Examples of X-linked conditions include fragile X syndrome (FXS), haemophilia A and B, and Duchenne muscular dystrophy. If a woman is a carrier of an X-linked condition, she has a one in four chance of having a son with that condition in each pregnancy (Figure 1b). Examples of autosomal recessive conditions include cystic fibrosis (CF), spinal muscular atrophy (SMA) and Tay-Sachs disease (TSD). If both members of a couple are carriers (heterozygous) for an autosomal recessive condition, they have a one in four chance with each pregnancy to have a child affected by that condition (Figure 1a). 2 Many of these are inherited in an autosomal recessive or X-linked fashion. There are >5000 conditions for which the genetic basis has been elucidated, and this number is increasing weekly. 1 In the 2018 federal budget, Mackenzie’s Mission, a $20 million Medical Research Future Fund research project investigating carrier screening, was announced the aim of Mackenzie’s Mission is that carrier screening for inherited disorders will become freely available to all Australians. Such testing is available commercially, including as direct-to-consumer testing. One important risk for which GPs do not routinely offer testing to couples is the risk of autosomal recessive and X-linked genetic conditions that cause severe disabilities and significantly affect the quality of life for the child and their family. 1 Multiple tests are offered to identify potential risks to a couple’s future child, including testing for maternal infections and nutrient levels. GPs are able to provide preconception planning to optimise the health and wellbeing of the couple and their child. General practitioners (GPs) often care for women and couples who are preparing to start or continue their family.
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