Rapid and simple prenatal DNA diagnosis of Down's syndrome.

BACKGROUND: Prenatal diagnosis of chromosomal abnormality requires cytogenetic analysis of amniotic fetal cells. The necessary culture time delays diagnosis, is expensive, and requires substantial scientific expertise. In a masked prospective study, we investigated the feasibility of PCR amplification of chromosome 21 markers for the prenatal diagnosis of Down's syndrome. METHODS: The study population consisted of 2167 pregnant women, undergoing amniocentesis for prenatal diagnosis. In this cohort at least 1.5 mL amniotic fluid was available surplus to the requirements for traditional diagnostic methods. DNA was extracted from the surplus amniotic fluid and amplified in fluorescence-based PCR reactions, with three small-tandem-repeat markers located on chromosome 21. The products of the reactions were analysed on a DNA sequencer to identify the presence of two or three copies of chromosome 21. FINDINGS: In 2083 (97.4%) of 2139 samples of amniotic fluid that were not macroscopically blood-stained, two DNA markers gave an informative and correct result, identifying 2053 fetuses as normal and 30 as having trisomy 21 Down's syndrome (as confirmed by cytogenetic analysis). An extra marker was informative in 32 of 41 other clear samples. Thus a total of 99.6% informative results was achieved with these three markers. Macroscopically blood-stained samples (28 [1.3%]) were unsuitable for DNA testing. They gave a typical but non-informative result. There were no false-positive or false-negative results. INTERPRETATION: The PCR-based DNA diagnostic test has great potential for improved prenatal diagnosis of Down's syndrome, with the advantage that results may be available within a day.

Amniotic fluid acetylcholinesterase in the prenatal diagnosis of open neural tube defects and abdominal wall defects: a comparison of gel electrophoresis and a monoclonal antibody immunoassay.

Stored amniotic fluid samples collected in Oxford and East Birmingham as part of the Collaborative Acetylcholinesterase Study were assayed for the presence of acetylcholinesterase (AChE) using a monoclonal antibody (4F19) enzyme antigen immunoassay. These results were compared with the results of a gel AChE which had been performed earlier. A total of 5689 samples from singleton pregnancies were analysed (including 36 with anencephaly, 77 with open spina bifida and 17 with anterior abdominal wall defects). The gel test yielded detection rates of 97% for anencephaly, 99% for open spina bifida and 94% for abdominal wall defects; the false positive rate (excluding pregnancies associated with serious abnormalities, miscarriages and intrauterine deaths) was 0.24%. The monoclonal test yielded similar results; using appropriate cut-off values to allow for differences in acetylcholinesterase levels in blood stained and clear samples, a similar false-positive rate of 0.22% was associated with detection rates of 97%, 95% and 71% respectively for the three types of defect. Although the detection rates and the false positive rate were slightly higher for the gel test, a result that might be explained by a decrease in AChE activity caused by storage of the samples, the monoclonal test has the advantages of requiring less interpretative expertise, it can be performed on a larger number of samples a day and it is not affected by contamination with fetal calf serum.

Primary cerebral rhabdomyosarcoma and the problem of medullomyoblastoma.

A case of primary rhabdomyosarcoma in the right cerebral hemisphere of a 45 year old woman is reported. This was treated by surgical excision but death occurred 10 months after the first symptom. The histogenesis of such a tumour is discussed. The clinical and pathological features of 15 previously reported similar tumours of the CNS are compared. Most of these occurred in the cerebellum in children where they have been regarded as medullomyoblastomas (a variant of medulloblastoma), teratomas, or rhabdomyosarcomas. Few have been recorded in adults and only one previously in the cerebrum. All of these tumours tend to have a short clinical course, although survival time seems to be significantly improved by surgical excision followed by radiotherapy. The remarkable morphological similarities between the tumours are discussed. Argyrophilic fibrils were demonstrated in the present case and in an unrelated rhabdomyosarcoma of the jaw. This observation may invalidate the main criterion used for separating medullomyoblastomas and teratomas from rhabdomyosarcomas in this group of tumours. It is concluded that at present all these tumours should be regarded as rhabdomyosarcomas.

Intrafollicular amyloid in primary hyperparathyroidism.

The histology of the parathyroids from 88 cases of primary hyperparathyroidism has been reviewed in a search for local amyloid deposits. Characteristic intrafollicular amyloid deposits of varying extent were found in nine cases. The case histories of these show that seven had suspected or proven pluriglandular adenomatosis but that the remainder had no such associations. The material studied shows no correlation with systemic primary or secondary amyloidosis. The significance of these findings is discussed in relation to the pluriglandular syndrome, peptide hormones, medullary carcinoma of the thyroid, and calcitonin secretion. It is suggested that amyloid in this context may be a ;marker' for secretion of a peptide closely related to calcitonin.