Otto van Diggelen, Gerard Geilen and Joke Keulemans are members of the Enzyme Laboratory of the Clinical Genetics Department of the Erasmus University in Rotterdam.

The various units of the Department deal with all aspects of inherited disorders: Laboratory investigations of chromosomes, metabolites, enzymes and mutations in the DNA and also genetic counseling. Among the several thousand inherited diseases a couple of hundred are caused by defective enzymes. Patients who are suspected to have one of these diseases are referred to the Enzyme Laboratory by metabolic physicians.

In the laboratory blood or skin cells, or a tiny piece of liver or muscle, are investigated by determining the activity of the enzyme which is involved in the disease which the patients may have. If the Laboratory finds a deficiency of that enzyme activity, the exact diagnosis is established, allowing genetic counseling of the parents about the recurrence risk of having another child with the same disease. Enzyme analysis can also be used for prenatal diagnosis of these diseases.