37

PRENATAL DIAGNOSIS OF TWO HURLER FETUSESUSING AN IMPROVED ASSAY FOR

METHYLUMBELLIFERYL-&agr;-L-IDURONEDASE

SIR,-We have described’ a sensitive fluorimetric assay forot-L-iduronidase activity of cultured cells which we predictedwould permit prenatal diagnosis of Hurler’s disease. We nowreport a modification of this method resulting in even greaterdiscrimination between iduronidase deficient and control cells,and its application to the accurate detection of two fetuses withHurler’s disease.

Although the original method’ gives clear discriminationbetween control, iduronidase deficient (Hurler, Scheie, or doubleheterozygote) and heterozygous cells, we have found thatmean residual iduronidase activity of cultured fibroblasts fromfour Hurler patients was relatively higher (8-8%) than it waswhen measured with phenyl-(X-L-iduronide2,3 (2.2%) as sub-strate.

In view of the possibility that some of the residual activityis due to contamination of 4-methylumbelliferyl-(X-L-iduronideby the 5’-epimer, 4-methylumbelliferyl-p-D-glucuronide,4 wehave assayed cells for iduronidase activity with and without 20pmol/t D-saccharolactone (boiled potassium acid saccharate),an inhibitor of p-D-glucuronidase. ot-L-iduronidase is also inhi-bited by saccharolactone but to a lesser extent (Kj 0.69mmol/I) than p-glucuronidase (Kj 0.0012 mmol/1). S

Amniotic cells from two pregnancies at risk for Hurler’s dis-ease and controls were collected by amniocentesis at about 16weeks’ gestation and cultured. As shown in the table, release

IDURONIDASE ACTIVITIES OF CULTURED AMNIOTIC CELLS

*1 unit of activity is defined as nmol 4-methylumbelliferone released/h/mg protein.

of 4-methylumbelliferone during incubation (iduronidase ac-tivity) was reduced in 7 control amniotic cell cultures by 19-1%to 37.1% (mean 29.4%) by the addition of saccharolactone:and in the two Hurler amniotic cells by 78.7% and 64-3%.This differential inhibition of control and Hurler amniotic cell"iduronidase activity" in the presence of saccharolactone in-creased discrimination from 9.6% to 3.9% of control mean

1. Stirling JL, Robinson D, Fensom AH, Benson PF, Baker JE. Fluorimetricassay for prenatal detection of Hurler and Scheie homozygotes or hetero-zygotes. Lancet 1978; i, 147.

2. Hall CW, Neufeld EF. &agr;-L-iduronidase activity in cultured skin fibroblastsand amniotic fluid cells. Arch Biochem. Biophys 1973; 158, 817-821.

3. Bach G, Cantz M, Hall CW, Neufeld EF. Genetic errors of mucopolysac-charide degradation. Biochem Soc Trans 1973, 1, 231-234.

4. Hopwood JJ, Muller V, Smithson A, Baggett N. A fluorimetric assay using4-methylumbelliferyl &agr;-L-iduronide for estimation of &agr;-iduronidase acti-vity and the detection of Hurler and Scheie syndromes. Clin Chim Acta,1979, 92, 257-265.

5. Weissman B, Santiago S. &agr;-L-iduronidase in lysosomal extracts. BiochemBiophys Res Commun 1972, 46, 1430-1433.

values. Both pregnancies were terminated and iduronidasedeficiency was confirmed in both fetuses using phenyI-<x-L-idur-onide as the substrate (phenyliduronidase activity in fetuses 1and 2 were 0.70% and 0. 39% of control, respectively).We conclude that the specificity of assay for 4-methylumbelli-

feryl-ot-L-iduronidase in cultured amniotic cells is increasedwhen the incubation is done in the presence of saccharolactoneand that the assay is reliable for prenatal diagnosis of Hurler’sdisease.

We thank Mr E. E. Vickers of Koch-Light Laboratories Ltd for agenerous gift of MU-iduronide.

Department of Biochemistry,Queen Elizabeth College,London W8 7AH

JOHN L. STIRLINGDONALD ROBINSON

P&aelig;diatric Research Unit,Prince Philip ResearchLaboratories,

Guy’s Hospital Medical School,London SE1 9RT

ANTHONY H. FENSOMPHILIP F. BENSON

JANET E. BAKERLINDA R. BUTTON

ANTENATAL DETECTION OF CONGENITALADRENAL HYPERPLASIA

SIR,-The paper by Dr Pollack and colleagues (May 26,p. 1107) clearly shows the feasibility of using HLA typing forantenatal detection in congenital adrenal hyperplasia due to21-hydroxylase deficiency. Leaving aside the question ofwhether this is the best method available, it was sad that therewas no discussion of the ethical implications of antenataldetection with termination in a disease which with treatmentis compatible with normal life. In the course of a genetic sur-vey into this condition in Wales, parents were asked whetherthey would wish to take advantage of antenatal detection withtermination of an affected fetus if a reliable method becameavailable. Only two of twenty-six parents would opt for thiscourse, the rest being willing to risk a further affected child.The linkage between congenital adrenal hyperplasia and HLAis clearly of great scientific interest but is probably of relativelylittle nrncticql annlication.

Llandough HospitalPenarth, Glamorgan CF6 1XX J. R. SIBERT

REVERSIBLE CEREBRAL ATROPHY IN INFANTILESPASMS CAUSED BY CORTICOTROPHIN

SIR,-Cerebral atrophy as defined pathologically includestwo constant features, the loss of neurones and neuroglialovergrowth,’ both of which are irreversible. Therefore the

computer assisted tomographic brain scans (CT scans) shownby Dr Lagenstein and colleagues to demonstrate the reversibi-lity of cerebral atrophy,2 must be open to alternative interpre-tations.

Firstly, the apparently normal CT scans before and aftercorticotrophin (ACTH) may represent "cerebral swelling"superimposed upon an underlying cerebral atrophy, and theeffect of steroids is merely to unmask the atrophy. Radiologicalcerebral atrophy is a common finding in infantile spasms.3,4 35out of 79 children (44%) with infantile spasms who have hadCT scans at the Hospital for Sick Children have the radiologi-cal appearances of cerebral atrophy or hypoplasia (table).Although cerebral atrophy is also found on neuropathological

1. Cappell DF, Anderson JR. Muir’s textbook of pathology. 9 ed. London:Edward Arnold, 1971: 607.

2. Lagenstein I, Willig HP, Kuhne D. Reversible cerebral atrophy caused bycorticotrophin. Lancet 1979; i: 1246-1247.

3. Brett EM, Hoare RD. An assessment of the value and limitations of air ence-phalography in children with mental retardation and with epilepsy. Brain1969; 92: 731-742.

4. Gastaut H, et al. Computerised tomography in the study of West’s syndrome.Develop Med Child Neurol 1978; 20: 21-27.