Detection of mosaicism in amniotic fluid cultures: a CYTO2000 collaborative study

PURPOSE

To evaluate the assumptions on which the American College of Medical Genetics (ACMG) Standards and Guidelines for detecting mosaicism in amniotic fluid cultures are based.

METHODS

Data from 653 cases of amniotic fluid mosaicism were collected from 26 laboratories. A chi-square goodness-of-fit test was used to compare the observed number of mosaic cases with the expected number based on binomial distribution theory.

RESULTS

Comparison of observed data from the in situ colony cases with the expected distribution of cases detected based on the binomial distribution did not reveal a significant difference (P = 0.525).

CONCLUSIONS

The empirical data fit the binomial distribution. Therefore, binomial theory can be used as an initial discussion point for determining whether ACMG Standards and Guidelines are adequate for detecting mosaicism.

Duplication of 16q and deletion of 15q

A patient with distal arthrogryposis, congenital dislocations of the hips, a prominent forehead, epicanthal folds, thin lips, and a poorly defined philtrum was found to have a deletion of 15q and a duplication of 16q. Her mother, maternal grandmother, and great grandmother had a balanced t(15q-, 16q+). The gene for adenine phosphoribosyl transferase was assignable to the 16q22----16qter area that was duplicated.

Molecular characterization of human minichromosomes with centromere from chromosome 1 in human-hamster hybrid cells

In this study we examine the amounts of four different human satellite DNA sequences in a series of human-hamster hybrid cells, which contain a human minichromosome including the centromere of human chromosome 1. Comparisons with the corresponding amounts in an intact human chromosome 1 suggest that the minichromosomes have lost satellite DNA sequences, and in one case a substantial fraction of several satellite DNAs is lost, without affecting the stability and normal mitotic segregation of the minichromosome. The smallest minichromosome appears to have lost all of the long arm and a significant portion of centromeric heterochromatin, while retaining 1000-2000 kb of the short arm of human chromosome 1. The satellite sequences examined include: a chromosome 1-specific satellite III probe, a chromosome 1-specific alpha satellite DNA, another alpha satellite DNA originally derived from the X chromosome, and an alphoid EcoRI dimer whose isolation from one of the minichromosomes and characterization is also described in this paper. One interpretation of these data indicates that an interspersion of blocks of satellite sequences occurs in the centromere region of chromosome 1. If these satellite sequences have functional significance, then there may be redundancy in the system that allows for a variation in the size of the kinetochore and the number of attachment sites for microtubules.