[Advances in newborn screening and immune system reconstitution of severe combined immunodeficiency]

Severe combined immunodeficiency disease (SCID) is a group of rare congenital diseases characterized by severe deficiencies in T lymphocyte counts and/or function. The recurrent, persistent and severe infections are its clinical manifestations. Neonatal screening and immune system reconstruction would improve the prognosis of SCID children. Newborn screening programs based on T-cell receptor excision circles (TRECs) quantitative detection have been carried out in clinical practice, however, the methods still have some limitations. Other new methods such as mass spectrometry and T lymphocyte-specific biomarker assays are still under investigation. Hematopoietic stem cell transplantation and gene therapy are the two main methods for reconstructing immune function in SCID children. Through improving the success rate of transplantation and the long-term safety and stability of viral vectors, some achievements have been made by many centers already. However, large-scale prospective studies are needed for evaluation of the long-term efficacy. In this article, the recent progress in newborn screening and immune reconstitution of SCID is reviewed.

[Genetic analysis of newborns with abnormal metabolism of 3-hydroxyisovalerylcarnitine]

OBJECTIVE

To investigate the genetic characterization of 3-hydroxyisovalerylcarnitine (C5-OH) metabolic abnormality in neonates.

METHODS

Fifty two newborns with increased C5-OH, C5-OH/C3 and C5-OH/C8 detected by tandem mass spectrometry during neonatal screening were enrolled in the study. Genomic DNA was extracted from the whole blood samples of 52 cases and their parents. Seventy-nine genes associated with genetic and metabolic diseases including MCCC1, MCCC2 were targeted by liquid capture technique. Variation information of these genes was examined by high-throughput sequencing and bioinformatic analysis, and then was classified based on the American College of Medical Genetics and Genomics (ACMG) standards and guidelines. The genetic types were classified as wild-type, MCCC1-maternal-mutation, MCCC1-paternal-mutation and MCCC2-mutation. Wilcoxon rank-sum test was performed for the increased multiples of C5-OH calculated in neonatal screening.

RESULTS

Twenty one MCCC1 variants (14 novel) were identified in 37 cases, 6 MCCC2 variants (5 novel) in 4 cases. The increased multiple of C5-OH calculated in MCCC1-maternal-mutation and MCCC2-mutation groups were significantly higher than that in wild-type group (all P<0.05), while there was no significant difference between MCCC1-paternal-mutation group and wild-type group (P>0.05).

CONCLUSIONS

Mutations on MCCC1 and MCCC2 genes are the major genetic causes for the increased C5-OH in neonates, and maternal single heterozygous mutation can contribute to the moderately to severely increased C5-OH.

[Screening for hereditary tyrosinemia and genotype analysis in newborns]

OBJECTIVE

To analyze the results of screening for hereditary tyrosinemia (HT) in newborns and its clinical features and genotype.

METHODS

The HT screening was conducted among 2 188 784 newborns from November 2013 to November 2018. The tyrosine (TYR)/ succinylacetone (SA) levels were detected by tandem mass spectrometry (MS-MS). The clinical characteristics, genetic results and following up data of identified patients were analyzed.

RESULTS

The normal ranges (0.5%-95.5%) of TYR and SA were 34.5-280.0 μmol/L and 0.16-2.58 μmol/L, respectively. Three HT cases were confirmed with a detection rate of 1∶729 595. There was 1 case of tyrosinemia type Ⅰ (HTⅠ) (homozygous variations of c.455G>A in FAH gene), 1 case of tyrosinemia type Ⅱ(HTⅡ) (heterozygous variations of c.890G>T and c.408+1G>A in TAT gene), and 1 case of tyrosinemia type Ⅲ (HT Ⅲ) (homozygous variations of c.257T>C in HPD gene). The variations of c.890G>T, c.4081G>A of TAT and c.257T>C of HPD were novel. The positive predictive value of the screening was 3.4%. Case 1 (HTⅠ) with TYR and SA values of 666.9 μmol/L and 3.87 μmol/L respectively, presented cholestasis, mild elevated of liver enzyme and lactic acid, who were although fed with TYR and phenylalanine free milk, but died at 2 months of age. Case 2 (HTⅡ) with higher TYR (625.6 μmol/L) and normal SA at screening, received medical milk treatment; during the 7 months of follow-up the baby showed normal score of Bayley assessment and normal TYR without eye and skin symptoms. Case 3 (HT Ⅲ) with TYR of 1035.3 μmol/L and normal SA at screening; during the 29 months of follow-up the value of TYR fluctuated from 532.1 μmol/L to 1060.3 μmol/L due to irregular medical milk treatment, while the score of Bayley assessment was normal.

CONCLUSIONS

HT is rare in the southern Chinese population, and the gene spectrum is scattered. Early treatment with nitisinone is recommended in children with HTⅠ, otherwise the prognosis is poor; the prognosis of children with HTⅡ is good when early treated with special diet; the prognosis of children with HTⅢ needs to be determined with more data.

[Research progress on phenotype and genotype of hyperphenylalaninemia]

Hyperphenylalaninemia(HPA), an autosomal recessive disease, is the most common inborn error of amino acid metabolism, caused by the deficiency of phenylalanine hydroxylase(PAH) or tetrahydrobiopterin(BH4) which induced by mutations of genes. The accumulation of the clinical database and genetic information will enhance the development of novel personalized medicine and to provide more accurate and timely diagnostic and therapeutic approaches for HPA. This paper summarizes the correlations between HPA metabolism and PAH, BH4, pathogenic genes and their distributions in HPA, as well as the phenotypes and genotypes of HPA, so as to provide reference for personalized medicine for HPA.

Preventive Effect of L-Carnitine on the Disorder of Lipid Metabolism and Circadian Clock of Mice Subjected to Chronic Jet-Lag

Circadian clock plays an essential role in orchestrating daily physiology, and its disruption can evoke metabolic diseases such as obesity. L-Carnitine can reduce blood lipid levels, and ameliorate fatty liver through regulating lipid metabolism. However, whether L-Carnitine administration may affect the disturbance of lipid metabolism and circadian rhythm of mice induced by prolonged circadian disruption is still unknown. Herein, we investigated the effects of L-Carnitine on conditions of circadian clock and lipid metabolism through a chronic jet-lag mice model which was developed by reversing 12 h light/12 h dark cycle every 4 days for a continuous 12 weeks. Results showed that L-Carnitine administration significantly decreased levels of serum glutamic-oxaloacetic transaminase (GOT) and triglycerides (TG), which were remarkably elevated by chronic jet-lag. More importantly, quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that L-Carnitine supplementation would effectively counteract the negative alterations in gene expression which related to lipid metabolism (Srebp1, Acaca, Fasn, and Scd1), metabolic regulator (mTOR) and circadian rhythm (Bmal1, Per1, Cry1 and Dec1) in the liver of mice subjected to the chronic jet-lag. As a conclusion, L-Carnitine was partly effective in preventing the disruption of circadian clock and lipid metabolic disorders induced by the chronic jet-lag.