广州市原发性肉碱缺乏症新生儿筛查评估及SLC22A5基因变异谱特征

Newborn screening for primary carnitine deficiency and variant spectrum of SLC22A5 gene in Guangzhou

目的评估原发性肉碱缺乏症(PCD)新生儿筛查性能、优化筛查指标,并探讨广州地区PCD发病率及SLC22A5基因变异特点。方法广州市新生儿筛查中心采用串联质谱法对辖区内2015至2019年出生的200180名新生儿进行多种遗传代谢病筛查,以游离肉碱(C0)<10μmol/L伴多种酰基肉碱降低为PCD筛查阳性,召回新生儿及其母亲复查,复查仍阳性者进行SLC22A5基因测序确诊。回顾性分析筛查结果,同时以丙酰基肉碱与棕榈酰基肉碱之和(C3+C16)作为多种酰基肉碱的辅助量化指标,并评估其效果。PCD新生儿及PCD母亲所生新生儿血酰基肉碱水平比较采用独立样本t检验。以广州地区2395名健康儿童外显子测序中SLC22A5基因结果计算人群致病变异携带率,推算PCD发病率。结果在200180名新生儿中筛查阳性239例,阳性率0.12%,确诊PCD 37例,其中PCD新生儿15例,PCD母亲22例,新生儿PCD发病率为1/13345,分娩母亲人群PCD发病率约为1/9099,阳性预测值15.5%。初筛C0<10μmol/L共810例,增加量化指标(C3+C16),以C0<8.5μmol/L或C08.5~9.9μmol/L伴(C3+C16)<2μmol/L为阳性切值,则筛查阳性224例,确诊37例,不增加假阴性。PCD新生儿与PCD母亲所生新生儿两组间初筛C0及(C3+C16)水平差异均无统计学意义[分别为(6.2±2.4)比(5.0±1.8)μmol/L,(1.4±0.4)比(1.2±0.5)μmol/L,t=3.826、0.326,P=0.058、0.572]。7例PCD母亲有不同程度的晨起头晕、疲劳,其中1例在妊娠期出现心肌病。SLC22A5基因分析显示,PCD新生儿常见3种变异为p.S467C、p.F17L、p.R254X;PCD母亲及健康儿童常见3种变异均为p.S467C、p.F17L及p.R399W,罕见重型变异p.R254X。健康儿童SLC22A5基因致病变异携带率为1/65,推算人群PCD发病率为1/16500。结论PCD新生儿筛查可同时检出新生儿患者及母亲患者,增加多种酰基肉碱量化指标(C3+C16)<2μmol/L可改善新生儿PCD筛查性能。重型变异p.R254X在PCD新生儿中常见,而在PCD母亲和健康儿童中罕见,提示低估了广州地区PCD患病率,可能漏检部分PCD新生儿。

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 200180 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 10μmol/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 2395 healthy children in Guangzhou Women and Children's Medical Center through whole exon sequencing were analyzed.Results Among 200180 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 1/13345 in newborns and 1/9099 in mothers,respectively.The positive predictive value of this program was 15.5%.Taking cutoff values of C0<8.5μmol/L or C08.5~9.9μmol/L with(C3+C16)<2μmol/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<10μmol/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 1/16500.Conclusions Newborn screening can detect PCD both in newborns and mothers.Adding a quantitative biomarker(C3+C16)<2μmol/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.