Guidelines for preventive activities in general practice

Genetics

      1. Genetics

Genetics

Advances in genomic medicine will continue to have a growing role in general practice. Genetic tests are available for an increasing number of indications from preconception planning, during pregnancy, for neonates (newborn screening), during childhood and through to adult-onset familial diseases such as cancer, cardiac and neurodegenerative diseases. More detail is available in the RACGP Genomics in general practice1 resource.

Screening

Recommendation Grade How often References
Genetic carrier screening: Preconception and prenatal
All women/couples planning a pregnancy, or who are already pregnant, should have a comprehensive family history recorded to identify relatives with heritable genetic disorders, as well as the presence of consanguinity.
Practice point Prior to or in early pregnancy 1,2
Information on carrier screening for genetic conditions should be offered to all women planning a pregnancy or in the first trimester of pregnancy, regardless of family history or ethnicity.
Options for carrier screening include screening with a panel for a limited selection of the most frequent conditions (eg cystic fibrosis, spinal muscular atrophy [SMA] and fragile X syndrome), or screening with an expanded panel that contains many disorders (up to hundreds).
MBS items are available for carrier screening for cystic fibrosis, SMA and fragile X syndrome.
Practice point Prior to or in early pregnancy 1,2
Screening can be sequential or couple screening. In sequential screening, one member of the couple is screened (usually the woman since the woman’s carrier status for X-linked conditions is relevant) and the second member of the couple is only screened if the first member is a carrier of one or more autosomal recessive conditions. In couple screening, both members of the couple are screened at the same time.
  • All couples with a high chance of having a child with one of the conditions screened for should be referred for genetic counselling to be informed of available reproductive options and to assist with prenatal testing if the woman in the couple is found to have a high chance is pregnant when the result becomes known.
  • All pregnant women should be offered basic screening for thalassemia carrier status by a full blood examination at initial presentation. Screening with specific assays for haemoglobinopathies (eg high-performance liquid chromatography [HPLC] or serum protein electrophoresis [EPG], and haemoglobinopathy gene DNA testing) should be considered in high-risk ethnic or population groups (Mediterranean, African and Asian ethnicity).
 
Practice point Prior to or in early pregnancy 2
Prenatal screening for chromosomal conditions
Screening or diagnostic testing for women at risk of carrying a baby with fetal chromosomal and genetic conditions is voluntary and should only be undertaken as an informed decision by the pregnant woman.
Acceptable first-line screening tests for fetal chromosome abnormalities in the first trimester include either:
  • combined first trimester screening with nuchal translucency and serum pregnancy-associated plasma protein A (PAPP-A) and beta human chorionic gonadotropin (βHCG) measurements 
    OR
  • cell-free DNA (cfDNA)-based screening (also called non-invasive prenatal testing [NIPT]),* usually available from 10 weeks.
The choice of first-line screening test will depend on local resources, patient demographics and individual patient characteristics.

Pre-test counselling for cfDNA-based screening should include informed decision making regarding testing for fetal sex and sex chromosome aneuploidy. The potential for other unanticipated findings of relevance to maternal health (including maternal genomic imbalances) should be included in pre-test counselling.
 
Acceptable first-line screening tests for chromosome conditions in second trimester include:
  • maternal serum screening (MA + AFP + βHCG +UE3 +/– inhibin) and,
  • cfDNA-based screening.
The choice of first-line screening test will depend on local resources, patient demographics and individual patient characteristics.
 
If a screening test result indicates an increased chance of a chromosome or genetic condition, the woman should have access to genetic counselling for further information and support. The available options for prenatal diagnosis should be discussed and offered.
 
Practice point












 
First trimester where possible













Second trimester
1,3
Routine population-based screening for genome-wide chromosome abnormalities and microdeletion syndromes is not recommended due to the absence of well-performed clinical validation studies. Not recommended (strong) N/A 3
Familial hypercholesterolaemia (FH)
FH assessment should be conducted when an individual presents with:
  • clinical features such as tendon xanthomata
  • untreated low-density lipoprotein cholesterol (LDL-C) >4.9 in adults mmol/L
  • premature cardiovascular disease (CVD) or a family history of such (CVD aged <60 years).
 
Assess their probability of having FH using the Dutch Lipid Clinic Network (DLCN) criteria. Offer referral to a lipid disorders clinic if DLCN score ≥3.
 
While FH can be diagnosed clinically, a confirmatory DNA test allows for cascade screening within the family of an affected patient. There is MBS funding for genetic testing for FH. MBS item 73352 can only be ordered by a specialist physician to make the diagnosis; GPs can order the test for cascade screening in unaffected relatives.
 
Conditionally recommended Once off 1
Hereditary haemochromatosis (HHC)
Consider HHC in:
  • patients with liver disease of unknown cause, including those with suspected alcoholic liver disease
  • family members of patients with HHC
  • other increased risk groups – patients with atypical arthritis, cardiomyopathy, chronic fatigue, diabetes mellitus.
Test fasting transferrin saturation and serum ferritin.
 
Genetic testing for variants in the homeostatic iron regulator (HFE) gene, rebatable via the MBS, is recommended in:
  • individuals with suspected iron overload (ie fasting serum transferrin saturation >45% or serum ferritin >200 μg/L in females or >300 μg/L in males)
  • first-degree relatives of patients with HHC who are p.Cys282Tyr homozygous or p.Cys282Tyr/p.His63Asp compound heterozygous.
 
Conditionally recommended Once off 1,4
Breast cancer – refer to section on breast cancer.      
Colorectal cancer – refer to section on colorectal cancer.      
*NIPT is not available through the MBS or covered by private health insurance.

Case finding

Recommendation Grade How often References
Those identified with a family history of a specific inherited disorder should be offered referral to a genetic counselling service for information about carrier screening and prenatal diagnosis/preimplantation genetic diagnosis for the condition. Practice point Prior to or in early pregnancy 1,2

Individuals and couples should be supported with advice to make informed decisions about genetic testing that includes discussion of out-of-pocket expenses required for the test. MBS funding is available for a limited number of genetic tests, some of which can be accessed in general practice under specific criteria. (Note that NIPT is not available through the MBS, nor is it covered by private health insurance.) 

Family history remains an important tool in identifying individuals at increased genetic risk. Ideally, a three-generation family history should be collected on all patients where possible, including first-degree relatives (ie children, siblings, parents) and second-degree relatives (ie aunts, uncles, grandparents).5 The use of a family history screening questionnaire can help identify individuals who may require a more detailed assessment of their family history of cancer, heart disease or diabetes.

There are no additional recommendations for Aboriginal and Torres Strait Islander people.

The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) Position statement Prenatal screening and diagnostic testing for fetal chromosomal and genetic conditions3 provides specific recommendations related to genetic carrier screening in people of Eastern European (Ashkenazi) Jewish descent and women with multiple pregnancies.

Genomics in general practice | RACGP – includes a suite of concise summaries on various clinical topics in genetics and genomics:

Dutch Lipid Clinic Network (DLCN) criteria, Cardiovascular Genetics – Familial hypercholesterolaemia (2016), Diagnosis and management of familial hypercholesterolaemia – Position Statement | Cardiac Society of Australia and New Zealand

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Related documents

  Lifecycle-chart.pdf (PDF 0.12 MB)

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