Molecular tools have sparked a revolution in the diagnosis ofgenetic disorders. In the past, genetic diagnosis was basedexclusively on clinical criteria or on biochemical tests forthe gene product or the consequences of its absence. Clinicalcriteria can be ambiguous, however, and sometimes features ofan inherited disorder take years to develop, resulting in longperiods of uncertainty about the diagnosis. Biochemical testscan produce equivocal results and often require invasive orexpensive studies. Moreover, clinical criteria and biochemicaltests have severe limitations when used to identify carriersor make a prenatal diagnosis.
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