Many inherited disorders are identified indirectly by examining abnormalities in the genetic end products (proteins or metabolites) that are present in abnormal forms or quantities. So, rather than detecting the problem in the gene, biochemical genetic testing looks for unusual findings related to the pertinent proteins, such as their absence or the presence of unusual amounts of other substances due to the defect in the protein.
Many of our genes code for production of enzymes.  Enzymes are proteins that are folded into complex shapes that allow smaller molecules to fit into them. They work to speed up chemical reactions and all the complex processes needed for life need enzymes.  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 coding for an enzyme, the protein may not fold into its correct shape or 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 often called “inborn errors of metabolism”.
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.
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