Antenatal analysis of the human chromosomes

The spindle checkpoint and chromosome segregation in meiosis

The spindle checkpoint is a key regulator of chromosome segregation in mitosis and meiosis. Its function is to prevent precocious anaphase onset before chromosomes have achieved bipolar attachment to the spindle. The spindle checkpoint comprises a complex set of signaling pathways that integrate microtubule dynamics, biomechanical forces at the kinetochores, and intricate regulation of protein interactions and post-translational modifications. Historically, many key observations that gave rise to the initial concepts of the spindle checkpoint were made in meiotic systems. In contrast with mitosis, the two distinct chromosome segregation events of meiosis present a special challenge for the regulation of checkpoint signaling. Preservation of fidelity in chromosome segregation in meiosis, controlled by the spindle checkpoint, also has a significant impact in human health. This review highlights the contributions from meiotic systems in understanding the spindle checkpoint as well as the role of checkpoint signaling in controlling the complex divisions of meiosis.

Prenatal diagnosis of chromosome abnormalities

It is possible to define a group of prospective parents who are at risk of producing offspring with disability due to chromosomal abnormalities. Such individuals should have evaluation of the 15 or 16 week fetus by karyotype of amniotic fluid cells. The techniques and problems of such diagnostic procedures are discussed.

Amniotic fluid cells; prenatal sex prediction and culture

Sex chromatin studies were carried out on small amounts of amniotic fluid obtained by amniocentesis or from intact amniotic sacs removed at hysterotomy. Provided that satisfactory preparations were obtained the accuracy of fetal sexing was 87%. Nevertheless, in the management of a pregnancy in which there is a risk of a serious X-linked recessive disorder, repeat amniocentesis may be necessary to ensure satisfactory specimens.Of 90 samples of fluid cultured, satisfactory growth was obtained in 49; the success rate was not increased by the addition of stimulants to the culture medium. It is suggested that between the 13th and the 16th week of pregnancy is the optimum time for amniocentesis to obtain cells for culture, since sufficient cells are then present in a small volume of fluid and therapeutic abortion would still be possible once the results were available.

Antenatal diagnosis

The diagnosis of genetic disease in utero in early pregnancy is a new and exciting development with important applications in the management of families with a high risk of producing a child with an hereditary disorder. Techniques currently under investigation are briefly reviewed and include sex chromatin, cytogenetic and biochemical studies on amniotic fluid cells and the biochemical composition of amniotic fluid. The study of amniotic fluid and its contained cells would seem to offer a promising and important approach to the prevention of genetic disease.