[Newborn screening for primary carnitine deficiency and variant spectrum of SLC22A5 gene in Guangzhou]
Y L Huang1, C F Tang1, S C Liu1
1Guangzhou Newborn Screening Center, Guangzhou Women and Children's Medical Center, Guangzhou 510180, China.
Insights
Newborn screening using tandem mass spectrometry can detect primary carnitine deficiency (PCD) in both infants and mothers. Adding a biomarker (C3+C16) improves screening accuracy, potentially identifying more PCD cases.
Area of Science:
- Biochemistry
- Genetics
- Neonatal screening
Background:
- Primary Carnitine Deficiency (PCD) is a metabolic disorder affecting carnitine uptake.
- Newborn screening programs aim for early detection and intervention.
- Tandem mass spectrometry (MS/MS) is a key technology in newborn screening.
Purpose of the Study:
- To evaluate and enhance the performance of MS/MS-based newborn screening for PCD.
- To determine the incidence of PCD in Guangzhou.
- To investigate the molecular characteristics of the SLC22A5 gene in PCD patients.
Main Methods:
- Screening of 200,180 neonates using MS/MS for free carnitine (C0) and acylcarnitine species.
- Confirmation of PCD through biochemical markers and SLC22A5 gene sequencing.
- Retrospective evaluation of (C3+C16) as a biomarker and comparison of screening cutoffs.
Main Results:
- Identified 37 confirmed PCD cases (15 newborns, 22 mothers) with an incidence of 1/13,345 in newborns.
- Optimized screening cutoffs (C0<8.5 μmol/L or C0 8.5~9.9 μmol/L with (C3+C16)<2 μmol/L) reduced false positives without missing cases.
- Identified common SLC22A5 variants (p.S467C, p.F17L, p.R254X) in newborns, with p.R254X being rare in mothers and healthy children.
Conclusions:
- Newborn screening effectively detects PCD in both neonates and mothers.
- Incorporating (C3+C16) as a quantitative biomarker enhances PCD screening performance.
- The prevalence of the severe p.R254X variant suggests potential underestimation of PCD incidence in Guangzhou.
Abstract:
Objective: To evaluate and improve the performance of the newborn screening program for primary carnitine deficiency (PCD) based on tandem mass spectrometry and to investigate the incidence of PCD and molecular characteristics of SLC22A5 gene in Guangzhou. Methods: A total of 200 180 neonates born in Guangzhou from 2015 to 2019 were enrolled into the newborn screening program for PCD by tandem mass spectrometry at Guangzhou Newborn Screening Center. The positive results of screening for PCD was defined as free carnitine (C0) less than 10 μmol/L with decreased acylcarnitine species in dried blood spots of three to seven days after birth. Screen-positive newborns and their mothers were recalled for another blood spot sample. The diagnosis was confirmed based on decreased levels of C0 and acylcarnitine species in recalled blood spots and genetic analysis in SLC22A5 gene sequencing. The utility of using the sum of propionylcarnitine and palmitoylcarnitine (C3+C16) as a biomarker for acylcarnitine species in newborn screening was retrospectively evaluated. The levels of C0 and (C3+C16) at first screening were compared between newborns with PCD and newborns born to mothers with PCD by independent t test. The variant spectrum and known pathogenic variants carrier rate of SLC22A5 in 2 395 healthy children in Guangzhou Women and Children's Medical Center through whole exon sequencing were analyzed. Results: Among 200 180 neonates, 239 (0.12%) cases were screen-positive for PCD. A total of 37 patients including 15 newborns and 22 mothers had confirmed PCD. The incidence of PCD was 1/13 345 in newborns and 1/9 099 in mothers, respectively. The positive predictive value of this program was 15.5%. Taking cutoff values of C0<8.5 μmol/L or C0 8.5~9.9 μmol/L with (C3+C16)<2 μmol/L, the number of screen-positive cases would be reduced from 810 to 224 without additional false negative case, when compared with cutoff value C0<10 μmol/L only. Both levels of C0 and (C3+C16) at first screening were not significant difference between newborns with PCD and newborns born to mothers with PCD ((6.2±2.4) vs. (5.0±1.8) μmol/L, (1.4±0.4) vs. (1.2±0.5) μmol/L, t=3.826, 0.326; P=0.058, 0.572). Seven PCD mothers experienced moderate fatigue and dizziness in the morning. One of them presented with cardiomyopathy in pregnancy. Genetic analysis of the SLC22A5 gene showed that p.S467C, p.F17L, p.R254X were the three most common variants in newborns with PCD. In PCD mothers and healthy children, the p.S467C, p.F17L and R399W were the three most common whereas the severe variant p.R254X was rare. The population carrier rate for pathogenic variants was 1 in 65 and the estimated incidence of PCD was about 1/16 500. Conclusions: Newborn screening can detect PCD both in newborns and mothers. Adding a quantitative biomarker (C3+C16) <2 μmol/L into the newborn screening program can improve the PCD screen performance. The severe variant p.R253X was common in PCD newborns but rare in PCD mothers and healthy children, indicating that the current screening program maybe failed to detect all PCD newborns and under-estimated the incidence rate of PCD in Guangzhou.
