Prence E M, Zalewski I, Natowicz M R
Division of Medical Genetics, E.K. Shriver Center, Waltham, MA 02254, USA.
Am J Med Genet. 1996 Nov 11;65(4):320-4. doi: 10.1002/(SICI)1096-8628(19961111)65:4<320::AID-AJMG14>3.0.CO;2-W.
Tay-Sachs disease (TSD) is a neurodegenerative genetic disorder caused by a deficiency of beta-hexosaminidase A (Hex A) activity. To diagnose TSD and to screen for TSD heterozygosity, laboratories use an assay that exploits the differential thermolability of the major beta-hexosaminidase isoenzymes, Hex A and Hex B. At 50-52 degrees C Hex A is labile, and Hex B is stable. We previously noted that the stability of leukocyte Hex B at 52 degrees C varied significantly, depending on the sample concentration in the incubation mixture. We have now examined this phenomenon in enzyme from cultured cells used for prenatal and postnatal diagnostic testing. We found that fibroblast Hex A and Hex B behave similarly to the leukocyte isoenzymes. In control and TSD fibroblasts there was a linear correlation between Hex B thermostability and sample concentration; at lower sample concentrations Hex B was less stable than at higher concentrations. Dialysis of the samples prior to heat treatment did not change the thermostability properties of Hex B, indicating that the change in stability is not due to a soluble low molecular weight substance. Cultured amniotic fluid cell and chorionic villus cell Hex B had a similar, but less pronounced, instability at low sample concentrations. Therefore, the unusual thermolability properties of Hex B, first detected for leukocyte Hex B, were noted in multiple tissues. Based on these data, we suggest that the concentration of cell extract be stringently controlled when the heat-inactivation method is used for the pre- or postnatal diagnosis of TSD, and that supplementation with non-thermolability-based beta-hexosaminidase assays should be employed as needed.
泰-萨克斯病（TSD）是一种神经退行性遗传疾病，由β-己糖胺酶A（Hex A）活性缺乏引起。为了诊断TSD并筛查TSD杂合性，实验室使用一种利用主要β-己糖胺酶同工酶Hex A和Hex B的不同热稳定性的检测方法。在50-52摄氏度时，Hex A不稳定，而Hex B稳定。我们之前注意到，白细胞Hex B在52摄氏度时的稳定性差异很大，这取决于孵育混合物中的样品浓度。我们现在已经在用于产前和产后诊断测试的培养细胞的酶中研究了这种现象。我们发现成纤维细胞Hex A和Hex B的行为与白细胞同工酶相似。在对照和成纤维细胞性TSD中，Hex B热稳定性与样品浓度之间存在线性关系；在较低样品浓度下，Hex B比在较高浓度下更不稳定。热处理前对样品进行透析不会改变Hex B的热稳定性特性，这表明稳定性的变化不是由于可溶性低分子量物质引起的。培养的羊水细胞和绒毛膜绒毛细胞Hex B在低样品浓度下具有相似但不太明显的不稳定性。因此，最初在白细胞Hex B中检测到的Hex B不寻常的热稳定性特性在多种组织中都有发现。基于这些数据，我们建议在使用热灭活方法进行TSD产前或产后诊断时，应严格控制细胞提取物的浓度，并应根据需要采用基于非热稳定性的β-己糖胺酶检测进行补充。
