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Biochemical genetic testing involves the study of enzymes in the body that may be abnormal in some way. Enzymes are proteins that regulate chemical reactions in the body. The enzymes may be deficient or absent, unstable, or have altered activity that can lead to clinical manifestations in an adult or child (i.e., birth defects).
There are hundreds of 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 (the gene product). The approach depends on the disorder. Biochemical genetic studies may be done from a blood sample, urine sample, spinal fluid, or other tissue sample, depending on the disorder.