6-丙酮酰-四氢蝶呤合成酶缺陷症的产前诊断

Prenatal diagnosis of 6-pyruvoyl tetrahydropterin synthase deficiency:application in a family

目的 对 6 丙酮酰 四氢蝶呤合成酶 (6 pyruvoyltetrahydropterinsynthase,PTPS)缺陷所致非经典型苯酮尿症家系先证者母亲现孕的第 3胎进行产前DNA突变分析 ,以确诊其是否受累。方法 用PCR和DNA测序在先证者及其父母身上找到PTPS基因突变。分离胎儿羊水细胞DNA ,以PCR 限制酶识别突变位点的方法进行基因突变分析 ;同时辅以高压液相 (HPLC)测定羊水中的生物蝶呤 /新蝶呤 +生物蝶呤比例 (B % ) ,对照该家系的尿生物蝶呤水平进行生化检查。结果 该家系先证者PTPS一对等位基因各有一 2 86G→A和 2 2 6C→T的突变 ,分别来自父母 ;先证者姨母也是 2 2 6C→T突变携带者 ,待测胎儿不含这两种突变。结论 对PTPS基因而言 。

Objective Defects in 6 pyruvoyl tetrahydropterin synthase(PTPS)may cause deficiency of tetrahydrobiopterin (BH 4), the essential cofactor for the aromatic amino acid hydroxylases. Most cases with BH 4 deficient PKU, also known as atypical phenylketonuria, are deficient in PTPS. The affected children manifest not only hyperphenylalaninemia, but also severe neurological damage caused by deficiency of 5 hydroxytryptamine and catecholamine. The present study aimed at confirming if the third fetus in a family with atypical PKU children born due to autosomal recessive PTPS defects was affected by using laboratory examinations on gene mutation and biochemical analyses. In the case where the fetus is affected, a selective abortion or supplement of 5 hydroxytryptamine and catecholamine can be applied to correct or control the disease. Methods The clinical manifestations of the girl proband met the criteria of PTPS deficient PKU; a brother died at the age of two; both parents were normal in manifestation. She was biochemically identified as having BH 4 deficiency with only 3.7 of urine biopterin/( biopterin +neopterin) %(B%), which is much lower than normal. Both of her parents were diagnosed as BH 4 deficiency carriers with slightly lower B%. The mother was pregnant at that time, waiting for prenatal diagnosis. A sister of the mother needed gene check as well. DNAs from peripheral lymphocytes of the families and amniocytes of the fetus were extracted. DNA sequencing and PCR endonuclease digestion were performed to check for mutations. Pteridines (biopterin and neopterin) in the amniotic fluid and urine were assayed by using high pressure liquid chromatography. Results The proband of the family carried two mutations on each of the PTPS alleles, the 286G→A from her father and 226C→T from her mother. And the sister of the mother also carried the same mutation found in mother. But the fetus was confirmed to have none of the two mutations. The urine HPLC results of the family showed that B% of the father and mother were 38.6 and 51.8, respectively, and that of the proband was 3.7. But the B% in the supernatant of amniotic fluid was as high as 65.0. Conclusion This fetus (the third of the family) was diagnosed to be homologous normal on PTPS gene. A normal phenotype has been confirmed by clinical manifestation, biochemical tests and repeated DNA check on the newborn baby girl.