NATIONAL SCREENING PROGRAMS FOR INHERITED DISEASES
A number of factors need to be considered before a screening program for any inherited disease is instituted. These include:
· does the disease have a relatively high incidence;
· can the disease be detected within days of birth;
· can the disease be identified by a biochemical marker that is easily measured;
· will there be a failure in diagnosing the disease early and would this cause irreversible damage to the baby;
· can the disease be treated and will the result of any screening test be available before irreversible damage to the baby occurs?
Thus, for example, neonatal screening programs for PKU are well established in practically all the countries of the developed world, including the UK. Any screening program has to be cost effective. Screening for PKU involves collecting a specimen of capillary blood from the baby at 6 to 10 days after birth, which allows for sufficient time for feeding and protein intake to become established. The test involves determining the concentration of phenylalanine in the plasma. If the result is indicative of PKU, further definitive tests are performed. The plasma phenylalanine concentration used to be determined by the Guthrie test, which involves determining the ability of plasma to support the growth of the bacterium Bacillus subtilis, which can only grow if phenylalanine is present in the medium. Nowadays, however, most laboratories use chromatographic, fluorimetric or mass spectrometric methods for the estimation of phenylalanine.