黏多糖贮积症Ⅱ型的诊断与产前诊断

目的建立用荧光底物测定艾杜糖-2-硫酸酯酶(IDS)活性的方法,应用该方法对黏多糖贮积症Ⅱ型(MPSⅡ)病例进行临床鉴别诊断,对高危妊娠的孕妇进行产前诊断。方法采用人工合成的荧光底物4-甲基伞形酮-α-艾杜糖苷-2-硫酸,测定 MPSⅡ疑似患儿血浆中 IDS 活性,并用绒毛或经培养的羊水细胞为检材,对高危妊娠的孕妇进行产前诊断。同时观察孕妇血浆 IDS 活性变化,用基因诊断方法检测胎儿性别。结果获得中国正常人 IDS 活性正常值:血浆中为240.2～668.2nmol/(4 h·ml),绒毛组织为37.2～54.9 nmol/(4 h·mg 蛋白),经培养的羊水细胞为21.4～74.4nmol/(4 h·mg 蛋白);患者血浆的 IDS 活性为0.3～18.6 nmol/(4 h·ml),肯定杂合子的血浆酶活性为88.7～547.9 nmol/(4 h·ml)。在50例疑似患儿中确诊了46例 MPSⅡ患者。10例产前诊断中检出4例男性胎儿患病,5例为女性胎儿。结论荧光法测定 IDS 活性是敏感、可靠、快速的方法,可用于病例鉴别诊断及孕早期 MPSⅡ高危妊娠的产前诊断。

Postnatal and prenatal diagnosis of mucopolysaccharidosis type II (Hunter syndrome)

OBJECTIVE: Mucopolysaccharidosis type II (MPS II, Hunter syndrome, OMIM 309900) is an X-linked recessive lysosomal storage disease resulting from a deficiency of iduronte-2-sulphate sulphatase (IDS). The present study aimed to establish an enzyme assay method for IDS activity for carrying out postnatal and prenatal diagnosis of MPS II by means of IDS activity assay on plasma, uncultured chorionic villi (CV) and cultured amniotic fluid cells (AF cell) using a new synthesized substrate. METHODS: A fluorigenic substrate (4-methylumbelliferyl-alpha-iduronate-2-sulphate, MU-alpha-Idu-2S) was used for the assay of IDS activity. IDS activity in plasma was determined for diagnosis of the proband. Prenatal diagnosis in 10 pregnancies at risk was carried out according to IDS activity on uncultured CV at 11th week or on cultured AF cell at 18th week of gestation. At the same time, IDS activity was also determined in the maternal plasmas to observe the change of IDS activity in pregnancy. The fetal sex determination was performed by PCR amplification of the ZFX/ZFY genes. RESULT: The IDS activity in plasma of normal controls and obligate heterozygotes were 240.2 - 668.2 nmol/(4 hxml) and 88.7 - 547.9 nmol/(4 hxml), respectively, while the enzyme activities in plasmas were in the range of 0.3 - 18.6 nmol/(4 hxml) in affected male. The IDS activities were 37.2 - 54.9 nmol/(4 hxmg protein) and 21.4 - 74.4 nmol/(4 hxmg protein) in CV and cultured AF cells respectively. Out of 50 suspected cases, 46 were diagnosed as having MPS II and 4 were excluded. Prenatal diagnosis was performed on 10 pregnancies at risk. Four of 5 male fetuses [IDS activity were 4.7, 1.8, 7.0 nmol/(4hxmg protein) in CV, 0.6 nmol/(4 hxmg protein) in AF cell] were diagnosed as having MPS II and the other 5 fetuses were normal females [IDS activity were: 48.7, 5.9, 25.2 nmol/(4 hxmg protein) in CV, 55.2, 40.9 nmol/(4 hxmg protein) in AF cell]. Increased IDS activity was observed in plasma of the pregnant women with unaffected fetuses, while the IDS activity decreased in pregnancies with affected fetuses. IDS activity of one female fetus was very low [5.9 nmol/(4 hxmg protein)], but the IDS activity in maternal plasmas increased, this fetus was a normal female. CONCLUSIONS: The method using a synthesized fluorigenic 4-methylumbelliferyl-substrate was a sensitive, rapid and convenient assay of IDS activity and was reliable for early prenatal diagnosis. Determination of fetal sex would be helpful in excluding the female fetus with low IDS activity from being considered as an affected male fetus. It would be further helpful if IDS activity in maternal plasma was taken into account.