Prenatal diagnosis of the fragile X--the Australasian experience.

Identification of increasing numbers of females heterozygous for fragile X linked mental retardation together with improved genetic counselling is creating a growing demand for prenatal diagnosis of fra(X). However, present cytogenetic techniques are somewhat unreliable and our collaborative approach has endeavoured to improve quality of cell culture systems and the sensitivity of fra(X) detection. Since 1985 we have exchanged cell cultures between our laboratories for verification of diagnostic results and comparison of induction techniques and have benefitted from larger numbers of cells scored for fra(X). Our 50 cases represent almost all of such studies undertaken in Australasia (Australia and New Zealand). Ten cases were unequivocally fra(X) positive; there was discrepancy between laboratories in 4 cases and one false-negative case. We propose a protocol to enhance fra(X) detection and conclude that, provided care is exercised, couples at risk of a fra(X) pregnancy can benefit from prenatal cytogenetic diagnosis.

Chorionic villus sampling: cytogenetic experience in preliminary investigations and in 50 diagnostic cases.

The results of preliminary cytogenetic investigations of chorionic villus sampling (CVS) and its diagnostic application in 50 cases are reported. Preliminary investigations included the effect of short delays between biopsy and processing, levels of mitotic activity related to variations in processing, the incidence of tetraploidy, correlation of the karyotype of the chorionic villi with that of the fetus, and the results of banding studies. A protocol was then designed for application to diagnostic CVS. The 50 diagnostic cases included 4 with male karyotypes which were terminated due to a family history of an X-linked disorder, 1 trisomy 21, 1 trisomy 18, the finding of 1 aberrant cell out of 50 in an otherwise normal analysis, a 45, XY, t (13;21) karyotype, 2 fragile X negative karyotypes and in one case the presence of mosaicism was detected in chorionic villi and subsequently not confirmed at amniocentesis. The karyotype on the chorionic villi was 46XY/47XY +3.

Congenital abnormalities: "is it wise to have another child?".

Congenital abnormalities affect some five per cent of all live births, and are a major factor in childhood morbidity and mortality. Most physicians, therefore, encounter a variety of developmental disorders, and must frequently deal with problems faced by a handicapped patient and his family. This task is becoming increasingly difficult with the growth and sophistication of genetic knowledge and changes in society's attitude toward medical practice. Although congenital abnormalities are classified according to a variety of presumed genetic or environmental 'causes', it is important to remember that most developmental disorders result from complex interactions of genes and environment, and that time is an important factor. Optimal understanding of a congenital defect may, therefore, be best achieved by study of a patient within the wider context of his family. The family history is one of the most powerful tools available in establishing a diagnosis and in answering parents' questions concerning prognosis and recurrence risk. Ultimately, however, decisions based on genetic counselling must be made by the parents themselves, within the context of their own fears, beliefs and aspirations.

Dermatoglyphics in children with acute leukaemia.

The dermatoglyphics of 135 children with acute leukaemia differed significantly from those of normal controls, and examination of 174 of the patients' first degree relatives indicated that familial factors were involved. The findings suggested that within the racial group studied dermatoglyphics may partly identify a population subgroup which is at increased risk of leukaemogenesis. While these observations may not have immediate clinical application, they are likely to contribute to a greater understanding of individuals who have increased constitutional susceptibility to leukaemia.