Newborn screening (NBS) is a public health service aimed at identifying infants with severe genetic disorders, thus providing effective treatment early enough to prevent or ameliorate the onset of symptoms. Current NBS uses biochemical analysis of dried blood spots, predominately with timeresolved fluorescence immunoassay and tandem mass spectrometry, which produces some false positives and false negatives. The application of enzymatic activity-based testing technology provides a reliable screening method for some disorders. Genetic testing is now commonly used for secondary or confirmatory testing after a positive result in some NBS programs. Recently, next-generation sequencing (NGS) has emerged as a robust tool that enables large panels of genes to be scanned together rapidly. Rapid advances in NGS emphasize the potential for genomic sequencing to improve NBS programs. However, some challenges still remain and require solution before this is applied for population screening.

Background: Isovaleric acidemia (IVA) is an inborn error of leucine metabolism and different approaches have been applied to its prenatal diagnosis. However, systemic application of a biochemical strategy is rare. To evaluate its reliability and validity, we conducted a retrospective study of our experience with metabolite measurement together with genetic analysis in IVA prenatal diagnosis at a single center.Methods: A total of eight pregnancies whose probands were diagnosed as IVA were referred to our center for prenatal diagnosis. Prenatal data of genetic analysis and metabolite measurement using tandem mass spectrometry (MS/MS) and gas chromatography/mass spectrometry (GC/MS) in amniotic fluid (AF) samples were retrospectively reviewed.Results: Genetic and biochemical results were both available in these eight at-risk fetuses. Among them, two fetuses had higher levels of isovalerylcarnitine (C5) and C5/acetylcarnitine (C2) in AF compared with normal reference range and, thus, were determined to be affected, both of whom were found to carry compound heterogeneous mutations according to genetic analysis. The remaining six fetuses were determined to be unaffected based on a normal AF metabolite profile, except one showed slightly elevated C5 and they were found to be carriers according to genetic analysis. However, the level of isovalerylglycine (IVG) could not be detected at all in both groups.Conclusion: The biochemical analysis, as a quick and convenient method, could be an additional reliable option for the prenatal diagnosis of IVA, especially in families with inconclusive genetic results, and can achieve a more precise diagnosis in conjunction with mutation analysis.

Background cblC defect is the most common type of methylmalonic acidemia in China. Patients with late-onset form (>1 year) are often misdiagnosed due to heterogeneous symptoms. This study aimed to describe clinical characteristics and evaluate long-term outcomes of Chinese patients with late-onset cblC defect. Methods A total of 85 patients with late-onset cblC defect were enrolled. Clinical data, including manifestations, metabolites, molecular diagnosis, treatment and outcome, were summarized and analyzed. Logistic regression was used to analyze the factors influencing the prognosis of patients. Results The median age at disease onset and median time delay from initial symptoms to diagnosis were about 8.6 years old (ranging from 2 to 32.8 years old) and 2 months (ranging from few days to 20 years), respectively. Patients with late-onset cblC defect presented neuropsychiatric symptoms (68.2%), renal involvement (20.0%), cardiovascular disease (8.2%) and metabolic crises (3.5%) as first symptoms, which seemed to be age-associated. Disease progressed in most patients. Overall, cognitive decline is the most frequent symptom. The level of propionylcarnitine, propionylcarnitine / acetylcarnitine ratio, methylmalonic acid, methylcitric acid and homocysteine, were decreased remarkably after treatment( (P<0.001). 24 different mutations of MMACHC were identified in 78 patients, of which two were novel. The c.482G >A was the most frequent mutated alleles in this cohort (25%). Except 16 patients were completely recovered, the remaining patients still left with various severities of sequel in a long-term follow-up. The available data of 76 cases were analyzed by logistic regression, and the results showed that the time from onset of symptoms to diagnosis was significantly associated with the prognosis of patients (P < 0.05). Conclusions The diagnosis of late-onset cblC defect is often delayed due to poor awareness of its various and nonspecific symptoms, thus leading to a significant disability. It should be considered in patients with unexplained neuropsychiatric, renal and cardiovascular diseases or even multiple organ damage. Early diagnosis and prompt initiation of therapy are essential for the improvement of prognosis.