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Biochemical genetic testing involves the study of enzymes in the body which may be abnormal in some way. They may be deficient or absent, unstable, or have altered activity which can lead to clinical manifestations in a child (i.e., birth defects). These types of disorders are usually called "inborn errors of metabolism" since they are present a birth and affect how the body's metabolism works. "Metabolism" is a term which describes how the body converts food to energy, and then gets rid of the waste products.
There are more than 200 enzyme defects that can be studied in humans. Sometimes, rather than studying the gene mutation which is causing the enzyme to be defective in the first place, it is easier to study the enzyme itself (which is the product of the gene). The approach depends on the disorder. For example, mutations in the gene which causes Tay Sachs disease can be studied, but are not 100 percent accurate. By performing a laboratory test for the enzyme that is deficient in Tay Sachs, you can pick up more cases than through DNA testing. Biochemical genetic studies may be done from a blood sample, urine sample, spinal fluid, or other tissue sample.
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