SCREENING FOR CYSTIC FIBROSIS AND DOWN’S SYNDROME

Screening for Cystic Fibrosis Carrier Status

Cystic fibrosis is an inherited disease that affects the lungs and digestive system. It causes thick mucus to build up in the lungs and the gut, causing recurrent lung infections and poor digestion of food. People affected by cystic fibrosis have a decreased life expectancy and often die in their 30s or 40s.

In Australia, 1 in 2,500 babies are born with cystic fibrosis. For a child to be born with this condition, they must have inherited a gene for cystic fibrosis from each parent and therefore have 2 cystic fibrosis genes. People with one cystic fibrosis gene and one normal gene are carriers of cystic fibrosis but are completely healthy themselves. 1 in 25 Caucasian and 1 in 90 Asian people carry the cystic fibrosis gene.

All newborn babies are tested for cystic fibrosis as part of the heel-prick test which is done in hospital after birth. It is now possible to test to see whether you are a carrier of cystic fibrosis and therefore determine your risk of having a child with this condition.

Screening for Fragile X Syndrome Carrier Status

Fragile X is an inherited condition causing intellectual disability as well as behavioural and learning difficulties, as well as autism, anxiety and epilepsy. The features of fragile X syndrome can vary from mild to severe. It affects males more than females. A female carrier of fragile X syndrome may also experience early menopause.

In Australia, 1 in 4,000 people have fragile X syndrome. This condition is caused by a lengthening of a gene on the x chromosome. The longer the length of the gene, the worse the condition. The gene can lengthen when passed down through generations of a family. 1 in 150 people are carriers of fragile X syndrome. Newborn babies are not routinely tested for fragile X at birth. It is now possible to test to see whether you are a carrier of fragile X syndrome, and therefore determine your risk of having a child with this condition.

Screening for Spinal Muscular Atrophy Carrier Status

Spinal Muscular Atrophy is an inherited disease that affects the nerves in the spinal cord and causes muscle weakness. Depending on the type of spinal muscular atrophy, this can be very severe and occur from birth, causing the child to die in infancy. Other types progress more slowly, with some people not showing symptoms until adulthood.

In Australia, 1 in 6,000 babies are born with spinal muscular atrophy. For a child to be born with this condition, they must have inherited a gene for spinal muscular atrophy from each parent and therefore have 2 affected genes. People with one spinal muscular atrophy gene are carriers but completely healthy themselves. 1 in 40 people carry the spinal muscular atrophy gene.

Newborn babies are not routinely tested for spinal muscular atrophy at birth. It is now possible to test to see whether you are a carrier of this condition and therefore determine your risk of having a child with spinal muscular atrophy.

The blood test to test for all 3 conditions costs $385 – payable to the laboratory. There is no Medicare rebate or Health Fund rebate for this test. It is possible to test for only 1 or 2 of the 3 conditions if you wish.

Screening for Down Syndrome

Down Syndrome is the most common chromosome abnormality among live-born babies. The affected person has an extra copy of chromosome 21, hence the term trisomy 21. People with Down Syndrome have a characteristic physical appearance, some level of intellectual disability, and some health and development challenges. Down syndrome is more common in children of older pregnant women.

AGE RISK

25 30 35 40 42
1 in 1,350 1 in 890 1 in 355 1 in 90 1 in 50

There are now 2 options for Down Syndrome screening:

Combined First Trimester Screening for Down Syndrome

This is the current standard screening test, and involves a blood test at approximately 10 weeks of pregnancy and an ultrasound at approximately 12 weeks of pregnancy. The results are combined with your age risk to give a more accurate risk result for you. 1 in 20 people receive a high risk result and need to have further testing such as an amniocentesis. This screening program detects 92% of babies with Down Syndrome. The blood test costs approximately $111, and Medicare card holders can access a rebate of about $42. The 12 week ultrasound costs approximately $250 and Medicare card holders can access a rebate of about $60.

Non-Invasive Prenatal Testing – Harmony or Percept Prenatal Test

This is a new test, only recently available in Australia. It involves a blood test taken after 10 weeks of pregnancy. This blood sample is tested for fragments of the baby’s DNA found in the mother’s blood. 1 in 1,000 people receive a high-risk result and need to have further testing such as an amniocentesis. This screening program detects 99% of babies with Down Syndrome. This blood test costs approximately $500, and there is no Medicare rebate. It is still recommended to have the 12 week ultrasound to check for other fetal abnormalities.

© Dr Sahar