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About genetic (and genomic) screening

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Genetic screening looks at your genetic material (usually DNA) to find out whether you carry DNA variants (or ‘gene faults’) that could affect your health in future, or the health of your children. Screening tests can be offered to individuals, community groups with a common ancestry or ethnic background, or the entire populations (such as newborn screening). Genetic screening that looks at a large number of genes, across the entire genome, can be called genomic screening.

Genetic carrier screening

Genetic carrier screening analyses a person’s DNA to look for genetic variants that may lead to genetic conditions in their future children. These variants are sometimes called gene faults because they disrupt the function of a particular gene. Being a genetic carrier means that a person has a fault in one copy of a particular gene, but does not have the condition because they have a second, working copy of that gene.

If a genetic carrier has a child with someone who is also a genetic carrier of the same condition, then there is an increased chance that their child will be born with or will develop the disease. A genetic carrier screening test can provide an individual or couple with information that may be used when planning a family.

If a carrier of a gene fault (orange dot) has a child with someone who also carries a fault in that gene, then there is an increased chance that their child will be born with, or develop, the condition.

People who are offered genetic carrier screening tests are not necessarily at increased risk for a particular genetic condition. However, certain genetic diseases can be more common in particular community groups or populations. A number of genetic conditions occur more often in the Jewish community than other populations. These include the nine conditions currently included in the Community Genetics Program (NSW), along with others that are not yet included in current screening programs.

In NSW, genetic carrier screening has been offered to students and community members with Ashkenazi Jewish ancestry for more than 25 years. As a result of these screening programs, the rate of occurrence of serious genetic disorders has decreased or even disappeared in the tested community.

Reference

Lew RM, Proos A, Burnett L, Delatycki M, Bankier A, Fietz M. Tay Sachs disease in Australia: Reduced disease incidence despite stable carrier frequency in Australian Jews. Med. J Aust. 2012; 197(11/12):652-654. DOI: 10.5694/mja12.11010. PMID: 23230938

Screening for disease risk

Other types of genetic screening, for example for cancer or cardiac disease risk, can provide people with information about risks for their future health.

This type of screening focuses on variants across the genome that are known to cause or raise the risk of developing certain genetic conditions.

Genetic screening for disease risk can provide valuable information for an individual and their family members, who can then take steps manage their own risk.

Useful terms

What is a genome?

The entirety of a person’s genetic material encoded in their DNA: across more than 6,000,000,000 DNA letters.  This includes all their genes (approximately 20,000) and the genetic material between genes. Your genome contains the information to build your cells, your cells’ components, and their components’ components. It also carries the information necessary for the cells to function.

What is a gene?

A gene is a section of DNA that contains the information to produce a particular molecule (usually a protein) that the body needs to function properly

What is a variant?

A change or difference in the DNA sequence.

A variant is a place in the genome of an individual where the DNA code is different to the reference genome used by geneticists. If the variant causes a disease or raises a person’s risk of a person developing a genetic condition, it can be called a gene fault or mutation.

Everyone has 3-5 million variants across their genome. Most variants are harmless and common, but we all carry a number of variants that could affect our health and the health of our future children.

What is DNA sequencing?

DNA sequencing is a laboratory technique used to read the sequence of DNA bases — the units of DNA represented by the letters A, C, G, and T. In a sequencing laboratory, machines break the DNA up into manageable segments and read the order of the bases. Computers are then used to compare the DNA sequence with other sequences to locate the differences or variants.

The cost of DNA sequencing has dropped dramatically in the last decade. The first human genome sequences took years and cost more than a billion dollars to produce. Now, sequencing technologies can sequence a person’s whole genome- all six billion bases- in a few days.

What is a genetic condition?

A genetic condition is a health condition that is caused or linked with variants in our genetic material: usually DNA. Some genetic conditions are caused by DNA variants in both copies of a particular gene, others require only a single variant or gene fault, and others require involvement of variants across a number of genes.

Most DNA variants are harmless, but some can cause or raise a person’s risk of disease.

Some variants can prevent a gene from functioning — this is sometimes called a ‘gene fault’. The faulty gene may encode an altered protein, or change how much of the protein is made. This may then interrupt processes in the body, resulting in symptoms. Most genetic conditions result when both of the two copies of a gene are faulty. This is why carriers, who have only one copy of a gene fault, are not affected.