Newborn screening for homocystinuria

It is becoming increasingly apparent that pyridoxine responsive homocystinuria patients are being missed by newborn screening programs. The possibility that screening for homocystine, rather than the methionine, might be more effective was investigated by comparing homocystine and methionine levels of non-responsive patients at diagnosis. The plasma methionine levels of 11 infants were much more abnormal than the homocystine levels. Urine homocystine was low or not detectable and always less than methionine. Therefore, methionine determination is much more effective than homocystine determination for newborn screening for homocystinuria. It seems that a second blood specimen at a later age may be required to find the pyridoxine responsive infants.