Newborn screening aims to detect potentially fatal or disabling conditions in newborns as early as possible, often before the infant displays any signs or symptoms of a disease or condition. Usually multiple tests are done simultaneously using a few drops of blood from the newborn’s heel. Blood is tested for certain genetic, endocrine, and metabolic disorders. In order to test for a condition, there needs to be a broad, rapid test available that is relatively cheap, has a low false positive rate and high accuracy. Newborn screening is performed in individuals where there is no family history of a genetic condition. It is not used where there is a known family history – in these situations, other tests should be used to test the infant for the condition known in the family. Limited newborn screening is available to private patients in South Africa. There is no State newborn screening programme in South Africa.
Newborn screening for muscular dystrophy has not been widespread for a number of reasons. Firstly, there are many different conditions and thus designing a single test to detect the majority of these is not generally possible. This may change as genetic testing develops. Further, until recently no treatment existed to significantly alter the disease course and thus many would have argued against screening as early diagnosis would not have made any difference. This is changing as treatment advances.
Some countries are now screening for the commonest form of muscular dystrophy, Duchenne (DMD), by measuring the concentration of a type of protein called CK-MM, which is part of a group of proteins called creatine kinase. Creatine kinase is found in muscle tissue and CK-MM enters the blood stream in increased amounts when there is muscle damage or breakdown. Elevated levels of CK-MM detected by the kit may indicate the presence of DMD. Results showing elevated CK-MM must be confirmed using other testing methods, such as muscle biopsies, genetic testing and other laboratory tests. The current availability of drugs such as steroids, ataluren, eteplirsen and golodirsen, which may significantly alter the disease course if started early, makes screening for DMD justifiable.
Screening for spinal muscular atrophy (SMA) by genetic testing for the commonest fault worldwide – a deletion of both copies of the SMN1 gene – has also been introduced in some countries. New studies are suggesting that early diagnosis and initiation of treatment with drugs such as Spinraza® (Biogen) and Zolgensma® (Novartis) achieve best outcomes when started pre-symptomatically.