Chromosome studies to detect the folate sensitive fragile sites have been carried out on 2439 randomly selected neonates. Four autosomal fragile sites were detected in this group. Similar studies were carried out on referred patients, special school students and sheltered workshop employees. The incidence of fragile X in these groups was 6/1936, 13/502 and 0/128 respectively. Autosomal folate sensitive fragile sites were seen in 14/1936, 5/502 and 2/128 individuals respectively.

No abstract

Summary. Observations made on 31 amniotic fluid cell strains serially cultured until senescent are recorded. The cell strains had an average life in culture of 13-9 passages (range 3-29). The source of the amniotic fluid from which the cultures were initiated did not influence the behaviour of the cell strains. The behaviour ofthe cell strains was unrelated to the growth characteristics of the primary cultures from which they were derived. Cell strains derived from serial samples of amniotic fluid from three women were compared and their characteristics were no more related to each other than to the group as a whole. The cell types found in amniotic fluid cultures are described. The karyology of 12 of the cell strains was monitored and no significant changes from normal diploidy were seen. Possible reasons for the highly variable and unpredictable behaviour of amniotic fluid cell strains are discussed.

Older neonates: those who lived for more than one week but for less than 28 days.Where possible, chromosome studies were carried out

Six cases of chromosomal mosaicism detected in amniotic fluid cultures are described. In five of these there was no evidence of fetal mosaicism. In one case fetal mosaicism was demonstrated but only by the study of fibroblasts since blood cultures showed only normal cells. The implications of amniotic fluid mosaicism are discussed and it is concluded that this usually does not indicate fetal mosaicism. The value of repeated amnio‐centesis in the diagnosis of fetal mosaicism was demonstrated by findings in three of the cases. It is recommended that amniotic fluid cultures be harvested in situ for chromosome studies and that cytogenetic results be expressed as number of colonies karyotyped rather than as number of cells analyzed.