Genetic carrier screening

What is Genetic Carrier Screening?

Genomic Diagnostics’ genetic carrier screening tests for three of the most common inherited genetic conditions: cystic fibrosis (CF), fragile X syndrome (FXS) and spinal muscular atrophy (SMA).

One in 20 Australians will be a carrier for at least one of these conditions, however most will have no family history of disease.1 This is due to the relatively rare nature of the conditions and their inheritance patterns, either autosomal recessive or X-linked.

Carrier screening for CF, FXS and SMA is now funded by Medicare and should be offered to those considering pregnancy or in their first trimester.

Why screening is important?

Genetic carrier screening helps to inform reproductive decision-making.It gives carrier couples (where both partners are carriers for CF or SMA or the female partner is a carrier for FXS) the opportunity to consider a range of reproductive options.

When to offer screening?

RANZCOG recommends that information on carrier screening be offered to all women planning a pregnancy or in the first trimester of pregnancy. This includes screening for CF, FXS and SMA. The genetic carrier screening test can be easily added as part of a patient’s routine antenatal blood screening.

There is global consensus that genetic carrier screening is  performed before pregnancy. This gives your patients the widest range of reproductive choices and more time to make important decisions.

Carrier screening can still be offered in early pregnancy, although options will be more limited and time-sensitive.

The recommended screening pathway is to test the female partner first, followed by the male partner if the female is identified as a carrier for CF or SMA.

Genetic conditions screened  

CF, SMA and FXS can have devastating effects on life-expectancy and quality of life. The combined affected pregnancy rate for these disorders is equivalent to the population risk of having a child with Down syndrome.

Cystic Fibrosis

• Description: most common inherited disorder in Caucasians
• Carrier risk: 1 in 25
• People with the condition: 1 in 2,500
• Testing approach: testing for the 50 most common CFTR variants that are associated with more than 95% of CF cases
• Inheritance: autosomal recessive; both parents must be carriers to have an affected child

Fragile X Syndrome

• Description: most common form of inherited intellectual disability
• Carrier risk: 1 in 200
• People with the condition: 1 in 3,600 males, 1 in 6,000 females
• Testing approach: testing for triplet repeat expansions in the FMR1 gene that are associated with more than 99% of FXS cases
• Inheritance: X-linked; the mother must be a carrier to have an affected child

Spinal Muscular Atrophy

• Description: most common genetic cause of mortality in children under two
• Carrier risk: 1 in 35
• People with the condition: 1 in 10,000
• Testing approach: testing for the SMN1 gene deletion that is associated with more than 95% of SMA cases
• Inheritance: autosomal recessive; both parents must be carriers to have an affected child

Accuracy of screening results

Genetic carrier screening tests for the most common genetic changes associated with CF, SMA and FXS.

The assay can detect:

• >95% of cystic fibrosis carriers
• >99% of fragile X carriers
• >95% of spinal muscular atrophy carriers

The tests used for GCS are highly accurate diagnostic tests that reliably identify carriers for these conditions. However, genetic carrier screening cannot identify a small percentage of carriers (1-5%) because some very rare genetic variants cannot be detected by the test.