一例Pah基因杂合缺失合并半合子突变病例分析

Analysis of a case of Pah gene heterozygous deletion combined with hemizygous mutation

目的对一例苯丙氨酸羟化酶(PAH)缺乏症患儿进行基因组测序,分析其Pah基因变异情况,以明确病因。方法采用免疫荧光法对新生儿进行血苯丙氨酸(Phe)浓度检测,血Phe浓度>2.0mg/dL进行尿蝶呤谱分析以鉴别病因;进一步用基因测序技术对其静脉血进行Pah基因测序,测序数据与正常人基因组进行比对,分析基因变异情况。结果该患儿血Phe浓度为46.88 mg/dL(2765.92μmol/L),正常新生儿Phe浓度<2.0mg/dL,苯丙氨酸/酪氨酸(Phe/Tyr)为49.65(参考范围0.1~1.5),尿蝶呤谱结果为52.08(正常新生儿:19.8~50.3);基因测序结果发现1个缺失突变和1个剪接突变,分别为:exon6杂合缺失和第6外显子c.611A>G剪接突变,其中exon6片段缺失在人类基因突变数据库(HGMD)中未报道;患儿根据治疗前最高血Phe进行分类为经典型PAH缺乏症,需低Phe饮食治疗,并定期监测血Phe浓度水平。结论初步明确了该患儿的病因为杂合缺失合并半合子突变,Pah基因型为exon6杂合缺失/c.611A>G;并发现了1种未报道基因变异:exon6杂合缺失,扩展了苯丙氨酸羟化酶缺乏症基因数据库。

Objective The genome of a child with phenylalanine hydroxylase(PAH)deficiency was sequenced,and the PAH gene variation was analyzed to determine the etiology.Methods The blood phenylalanine(Phe)concentration of newborns was detected by immunofluorescence method.The blood Phe concentration was screened and analyzed by urinary pterin spectrum to identify the etiology,further,the Pah gene of venous blood was sequenced by gene sequencing technology.The sequencing data were compared with the genome of normal people to analyze the gene variation.Results The blood Phe concentration was 46.88 mg/dL(2765.92 mol/L),and the Phe concentration of normal newborns was<2.0 mg/dL.The phenylalanine/tyrosine(Phe/Tyr)was 49.65(reference range 0.1~1.5),and the result of urinary pterin spectrum was 52.08(normal newborns:19.8~50.3).The results of gene sequencing showed one deletion mutation and one splicing mutation,which were exon6 heterozygous deletion and exon6 c.611A>G splicing mutation,respectively.The deletion of exon6 fragment was not reported in human gene mutation database(HGMD).The children were classified as classic PAH deficiency according to the highest blood Phe before treatment.They needed low Phe diet treatment,and the blood Phe concentration level was monitored regularly.Conclusion It was preliminarily confirmed that the disease was caused by heterozygous deletion and hemizygous mutation.The Pah genotype was exon6 heterozygous deletion/c.611A>G.An unreported gene mutation,exon6 heterozygous deletion,was found,which expanded the gene database of phenylalanine hydroxylase deficiency.