Application of mass spectrometry in newborn screening: about both small molecular diseases and lysosomal storage diseases.

Many genetic diseases, especially the inborn errors of metabolism, have very low incidences, so developing a newborn screening test for each disease is not practical. This obstacle was overcome by employing the tandem mass spectrometry (MS/MS) technology. In the analysis, the samples can be injected directly into the flowing system without passing through a column, and both acylcarnitine and amino acid profiles can be obtained at the same time. MS/MS newborn screening has been shown to improve the outcome of patients affected by a number of inborn errors of metabolism. Recently, MS/MS analytical methods were developed for second-tier tests of newborn screening; new substrates have also been developed to measure the activity of lysosomal enzymes so lysosomal storage diseases can be diagnosed by MS/MS method now.

Early detection of glutaric aciduria type I by newborn screening in Taiwan.

BACKGROUND/PURPOSE: Glutaric aciduria type 1 (GA1) is an inborn error of lysine and tryptophan metabolism. There is a lack of initial diagnostic signs of the disease, but late treatment often results in severe neurologic impairment. In this study, we analyzed the results of screening for GA1 in a Chinese population. METHODS: Dry blood spots were obtained at about 3 days of age from 357,307 newborns and tested for elevation of glutaryl (C5DC)-carnitine by tandem mass spectroscopy. A second sample of blood spots was required from those cases with abnormal elevation of C5DC-carnitine (higher than the cut-off value) (recall). If the results remained abnormal, those cases were referred for confirmation of the diagnosis and treatment. RESULTS: Between August 2001 and February 2005, there were 40 cases with C5DC-carnitine more than 0.13 microM (the cut-off value), from whom a second sample of blood spots was obtained (recall rate, 0.02%); two cases were confirmed to be affected by GA1. Because of the low positive prediction rate using this cut-off value, we elevated the cut-off value slightly. Between February 2005 and August 2006, there were eight cases with C5DC-carnitine more than 0.22 microM from whom a second sample of blood spots was obtained (recall rate, 0.01%); three cases were confirmed to be affected by GA1. All five cases with persistent elevation of C5DC-carnitine were referred and diagnosis was confirmed in each, giving an incidence of 1 in 71,461 newborns. There were no false negatives. Magnetic resonance imaging studies obtained from four cases showed frontotemporal atrophy at the time of diagnosis. Two cases were followed for over 1 year, and under treatment with dietary control and carnitine supplementation, both had normal development and neither exhibited a frank episode of encephalopathic crisis. CONCLUSION: With properly established cut-offs, GA1 can be successfully screened for in populations with a low incidence of the disease. Early treatment is likely to improve the outcome of cases discovered by screening.

Tandem mass neonatal screening in Taiwan--report from one center.

BACKGROUND/PURPOSE: Neonatal screening using tandem mass spectrometry (MS/MS) started in Taiwan in 2000. We evaluated the efficacy of this system by analyzing the frequency of diseases and the outcome of the patients identified. METHODS: Between August 2001 and July 2004, 199, 922 neonates were screened for 10 amino acids and acylcarnitines using MS/MS in a single center. RESULTS: In total, 29 cases of inborn errors of metabolism were detected. The overall prevalence was one per 6894 births. The most common inborn error found was 3-methylcrotonyl CoA carboxylase deficiency (10 cases, 34.5%), but none of the cases needed aggressive treatment. There were two cases of type I glutaric aciduria, two cases of maple syrup urine disease, and one case of type II citrullinemia, and early therapeutic intervention was effective for all of them. CONCLUSION: We found that MS/MS neonatal screening was valuable in the early diagnosis of severe and treatable inborn errors of metabolism such as organic acidemias and urea cycle disorders. It also detected less severe disorders that required only observation.