[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.