Summary

• Biochemical genetics looks at how inherited gene mutations affect normal body processes, especially metabolism.
• Biochemical genetic testing is mostly used to investigate babies or infants thought to have an Inborn Error of Metabolism (IEM).
• It is often requested as a follow-up if a baby has an abnormal result from the newborn screen – the national program that tests babies soon after birth for IEM.
• It can also be used to investigate the reasons for an infant or child’s developmental delay, progressive weakness or symptoms such as seizures and vomiting.

What is biochemical genetics testing?

Biochemical genetics looks at how inherited gene mutations affect biochemical processes in the body, especially the way cells make, break down, or use substances such as sugars, fats, and hormones. These are known as metabolic processes.

Many of our genes hold the instructions for making enzymes. Enzymes are special proteins that are folded into complex shapes that allow smaller molecules to fit into them. They work to speed up chemical reactions. All the complex processes needed for life need enzymes.

These processes in our cells are called metabolism and they can be thought of as a series of steps leading to the conversion of one substance into another. The molecules at the beginning of the process are called substrates and the enzyme converts these into different molecules, called products.

If there is a change or mutation in the gene holding the instructions for making an enzyme, the enzyme that the gene makes may not work correctly. The enzyme may not fold into its correct shape, may be broken down too quickly or may not be produced at all. When this happens, the pathway gets blocked and the substrate builds up in the body and may be toxic.

Biochemical genetics looks for the increase in these substrates which can help us find the pathway and gene involved. These conditions are called inborn errors of metabolism. It is often not practical to look for changes in the many thousands of genes involved in metabolism so biochemical tests can help to pinpoint the pathways and genes involved.

If an enzyme works properly levels stay in the normal range. If an enzyme is not working properly some substances build up (accumulate) or other substances are low or missing (reduced).

Because there are so many pathways and different types of substrates, no one test can look for all the possible inborn errors of metabolism so the doctor requesting the test will need to choose the test based on the signs and symptoms the patient shows. Sometimes a few different tests are grouped together to make a metabolic screen, however, this will not find every possible condition and sometimes more specific tests or measurement of the enzyme itself will be required.

Why get tested?

Biochemical genetic tests will often be requested as a follow up to an abnormal newborn screening test.

The newborn blood spot screening (also known as the heel prick test) is a test done on all babies born in Australia. When the baby is born, several drops of blood are collected, and testing is done to identify if they have one of a range of conditions included in the inborn errors of metabolism screen. The blood is collected by pricking the baby’s heel which is why it is sometimes called the heel prick test.

Biochemical genetic tests may also be used later to see if an infant or child with unexplained neurological decline (such as progressive weakness), vomiting, lethargy, developmental delay or seizures has an inborn error of metabolism as the cause.

Rarely, some inborn errors of metabolism will present later in life and testing will be performed in adults.

There are many different types of biochemical tests which can be used to diagnose inborn errors of metabolism. Some of the more common tests include Amino acids, Organic acids and Acylcarnitines.

Having the test

Sample

Blood.

Preparation

None.

Your results

Many tests may be used in biochemical genetics. Your doctor will explain what your results mean and they may request further biochemical or DNA based genetic testing to confirm the diagnosis. Whereas biochemical tests can suggest what pathway is affected, DNA based testing can help confirm which gene is altered.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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