Variation in argininosuccinate synthetase activity in amniotic fluid cell cultures: implications for prenatal diagnosis of citrullinemia

Argininosuccinate synthetase activity was measured in amniotic fluid cells cultured from 25 normal fetuses and from 2 fetuses at risk for citrullinemia. Among the 25 control lines, argininosuccinate synthetase was low in epithelial-like cultures and high in more fibroblast-like cultures. The radioactivity incorporated from 14C-citrulline into protein was proportional to argininosuccinate synthetase activity. The activity of argininosuccinate lyase, the next enzyme in the urea cycle, was unaffected by a predominance of one or the other cell type. Argininosuccinate synthetase was low but detectable in cells from the two fetuses at risk for citrullinemia. The pregnancies were continued and both resulted in clinically normal females. Thus factors such as predominant cell type may affect area cycle enzyme activity in cultured amniotic fluid cells and should be taken into consideration in attempts to diagnose citrullinemia prenatally.

A family with different clinical forms of acid maltase deficiency (glycogenosis type II): biochemical and genetic studies

In the same family, the generalized or infantile form of acid maltase deficiency (glycogenosis type II, Pompe disease) and the muscular or adult-onset form affected different individuals. Autosomal-recessive inheritance for the two clinical forms was demonstrated in this family by assay of acid alpha-glucosidase in muscle, lymphocytes, cultured fibroblasts, and urine of asymptomatic relatives. Current biochemical techniques do not discriminate between persons heterozygous for the generalized form and those heterozygous for the muscular form. To explain the coexistence of both forms in the same family, the infant with the generalized form or her grandfather with the muscular form must have been a genetic compound of different mutant alleles for acid alpha-glucosidase.

Genetic heterogeneity and clinical variability in the Sanfilippo syndrome (types A, B, and C)

A study of 73 patients with the Sanfilippo syndrome (36 patients with Sanfilippo A disease, 23 with Sanfilippo B disease and 14 with Sanfilippo C disease) revealed both intertype and intratype variability. The course of the disease was relatively mild in Sanfilippo B disease and dementia was less severe. Type A showed earlier onset with more severe clinical manifestations and an earlier age at death. Sanfilippo C disease was slightly less severe than Sanfilippo A disease. The intratype variability may be explained in part by differences in genetic and environmental background. In Sanfilippo B disease, genetic heterogeneity is suggested by the observation of a more severe and a mild variant, and this variation may be due to the involvement of different allelic mutations. The intrafamilial variability of the different types was small, but in three families with Sanfilippo B disease intrafamilial variability was evident.

Trace element studies in three patients and a fetus with Menkes' disease. Effect of copper therapy

This paper reports the results of a multielement analysis of postmortem samples of Menkes patients, of which one was untreated and two had been treated for various lengths of time with intramuscular injections of copper-EDTA. The findings have been compared with data from a Menkes fetus and from controls. The results confirm that copper accumulates in various tissues and demonstrate a further increase in copper levels as a result of the treatment with copper-EDTA. Although no clinical improvement was observed, the levels of some copper-containing enzymes normalized during the copper-therapy. Furthermore, in agreement with the identification of the copper-binding protein in the kidney as metallothionein, it was found that not only copper, but also zinc, cadmium, and mercury are trapped in this tissue. A low copper concentration in the brain was also found in a Menkes fetus, indicating that brain damage might already have occurred before birth. Speculation Until recently, Menkes' disease was considered to be due to copper deficiency. However, the symptoms are more typical of a storage disease in which copper is irreversibly trapped in some tissues, in particular in the kidneys, by metallothionein. This abnormal storage pattern gives rise to copper deficiency elsewhere in the organism, particularly in the brain where it may cause irreversible damage in the foetus. Parenteral administration of copper does not lead to clinical improvement. The only "therapy" that seems feasible at present is tracing the carriers of the disease and advising abortion when prenatal diagnosis indicates a male fetus carrying the disease.

Identification of heterozygotes for glycogenosis 2 (acid maltase deficiency)

In 21 obligate and 9 possible heterozygotes for acid maltase deficiency (AMD) (glycogenosis 2, Pompe's disease), different methods of identifying heterozygotes have been studied. Heterozygosity could not be demonstrated by physical examination, serum CPK assays, morphological examination of muscle biopsy (including light-microscopy, histochemistry and electron-microscopy), or by ultrastructural examination of a skin biopsy. Heterozygotes could be identified to a large, but still limited extent, by measuring the acid alpha-glucosidase activity in urine, cultivated fibroblasts, leucocytes, or skeletal muscle. Heterozygotes for the generalized from of AMD could not be distinguished from those for the muscular form. The limitations of heterozygote identification by means of enzyme assays are discussed, and some practical aspects for genetic counselling are mentioned.

Intermittent neurological symptoms in a girl with a maple syrup urine disease (MSUD) variant

Severe neurological symptoms, including intermittent ataxia, hallucinations and convulsions, associated with metabolic acidosis and branched-chain amino-acidemia occurred in a six-year-old girl with a variant form of maple syrup urine disease. The symptoms only appeared during periods of infection. Between these periods the girl was healthy and the biochemical findings were normal. In later episodes of infection the condition was successfully treated with a low protein diet and sodium bicarbonate. Analyses of 1-14C-leucine decarboxylase in fibroblasts revealed 10 per cent of normal activity in the girl and 50-70 per cent in the parents. The importance of early diagnosis of MSUD variants is discussed. This is the first published Swedish case of MSUD variant.

Prenatal detection of a probable heterozygote for ADA deficiency and severe combined immunodeficiency disease using a microradioassay

A pregnancy at risk for adenosine deaminase deficiency and severe combined immunodeficiency disease has been investigated by assay of adenosine deaminase activity in cultured amniotic fluid cells using a microradioassay. A low-normal level of activity consistent with heterozygote status in the foetus was found and confirmed after birth by assay of red cell and fibroblast adenosine deaminase activities. It is suggested that the radioassay method offers significant advantages in sensitivity and specificity over the standard spectrophotometric procedure.

Prenatal diagnosis of xeroderma pigmentosum (group C) using assays of unscheduled DNA synthesis and postreplication repair

The analysis of DNA repair processes is described in two pregnancies at risk for xeroderma pigmentosum. In both cases, excision repair (measured by unscheduled DNA synthesis) and postreplication repair were analyzed. An affected and an unaffected fetus were identified within 3 weeks after amniocentesis. The cells from the affected fetus were found to be deficient in excision DNA repair, whereas the PRR patterns were intermediate between those of normal and PRR deficient cells. This indicates the possibility of prenatal diagnosis of PRR deficient XP patients (XP variants).

Prenatal monitoring for the Hunter syndrome: the heterozygous female fetus

An abnormal level of 35S-sulfate labeled mucopolysaccharides was found in cultured amniotic fluid cells from a pregnancy, at risk for the Hunter syndrome, with a female fetal karyotype. Subsequent prenatal analyses suggested heterozygosity for the X-linked Hunter syndrome, and this was confirmed by clonal analysis of fibroblasts of the child after birth. The possible implications of abnormal biochemical results in association with a female karyotype in the prenatal diagnosis of the Hunter syndrome are discussed.

An unexpected high frequency of trisomic fetuses in 229 pregnancies monitored for advanced maternal age

In 229 pregnancies monitored because of advance maternal age, 16 (7%) abnormal fetal karyotypes were detected. We found 13 cases of trisomy 21, twice a trisomy 18, and once an additional marker chromosome. The frequency of abnormal fetal karyotypes in different maternal age groups was found to increase from 1:20 at 38--40 years, to 1:16 at 41--43 years, and finally to 1:4.5 in women of 44--46 years. The overall incidence of chromosomal aberrations and specifically of trisomy 21 is considerably higher than that described in retrospective studies.

Limitations of visualization of the entire fetus by means of second-trimester fetoscopy

Fetoscopy with rigid fiber optics was performed under general anesthesia in 9 patients scheduled for therapeutic abortion by hysterotomy with a duration of pregnancy between 12 and 18 weeks. Visualization of fetus and placenta was found to be at random chance and incomplete, and could not be improved by internal or external manipulation. Skin biopsies were obtained in 5 cases. The cord could be recognized in all cases. It is concluded that the haphazard and incomplete visualization of the uterine contents at present precludes the application of second-trimester fetoscopy for early detection of visible congenital fetal abnormalities.

Rapid prenatal diagnosis of GM1-gangliosidosis using microchemical methods

Prenatal diagnoses were established in 3 pregnancies at risk for GM1-gangliosidosis at 9, 10, and 12 days after amniocentesis. Beta-galactosidase activities in cultured amniotic fluid cells were determined by microchemical assays in cell homogenates and in isolated groups of 10--30 freeze-dried cells. The latter method requires only a few hundred cells growing in one or more clones and will usually allow a diagnosis within 9--12 days after amniocentesis.

Prenatal diagnosis of genetic disorders

Three hundred and fifty pregnancies were monitored by transabdominal amniocentesis in the fourteenth to sixteenth week of gestation followed by karyotyping or biochemica assays of cultured amniotic fluid cells and analysis of alpha-fetoprotein in the amniotic fluid supernatant. The pregnancy was interrupted in 36 cases (10%) either becasue of a fetal abnormality or the presence of a male fetus in pregnancies at risk for an X-linked disease. Four chromosomal aberrations were found in 87 pregnancies tested because of advanced maternal age. In 101 pregnancies with a recurrence risk of Down's syndrome, 2 fetuses with an abnormal karyotype were detected. In 11 cases, in which 1 parent was a carrier of a balanced translocation, 2 unbalanced fetal karyotypes were found. Fetal chromosome studies in 43 pregancies at risk for an X-linked disease indicated the presence of a male fetus in 21 cases. Prenatal diagnosis of 11 different metabolic diseases was performed in a total of 34 cases. Microchemical techniques were used to allow completion of the diagnosis of seven different enzyme deficiencies within 9 to 22 days after amniocentesis. Alpha-fetoprotein assay in the amniotic fluid supernatant of 47 pregnancies at risk for an open neural tube defect resulted in the detection of 3 anencephalic fetuses during the second half of pregnancy. The safety and reliability of amniocentesis and the possible effects on the outcome of pregnancy are evaluated. Prenatal diagnosis offers a promising alternative for parents who are at risk of having a child with a genetic disease which can be detected in amniotic fluid or in cultured amniotic fluid cells.

beta-Galactosidase deficiency in an adult: a biochemical and somatic cell genetic study on a variant of GM1-gangliosidosis

Biochemical data are presented of a 29-year-old male, who shows progressive psychomotor retardation and a beta-galactosidase deficiency in leucocytes and cultured skin fibroblasts. Somatic cell hybridization studies show that this variant of GM1-gangliosidosis is based on a different gene mutation than is present in types 1 and 2. No complementation is observed in fusion experiments with cells from type 3 variant.

Prenatal diagnosis of type II glycogenosis (Pompe's disease) using microchemical analyses

1. In order to reduce the time interval between amniocentesis and prenatal diagnosis of Pompe's disease microchemical techniques were used for assay of acid alpha-1,4-glucosidase activities in cultured amniotic fluid cells. 2. Microtechniques used on homogenates of cultured amniotic fluid cells enabled the waiting period to be reduced to 2-3 weeks. 3. When dissected lyophilized groups of 200-300 cultured cells were analyzed, a prenatal diagnosis was possible at about 10 days after amniocentesis. 4. The acid alpha-1,4-glucosidase activity in the amniotic fluid supernatant is not informative in prenatal diagnosis of Pompe's disease. 5. Conditions of cell cultivation such as length of time in culture were found to influence markedly the acid alpha-1,4-glucosidase activity in cultured amniotic fluid cells. 6. For a reliable prenatal diagnosis of metabolic disorders primary cultures of control amniotic fluid cells should be used and the analytical results from the pregnancy at risk should be compared with primary cultures of control amniotic fluid cells and with those in cultured fibroblasts from heterozygous carriers, and an affected sibling from the particular family.