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.

Chromosome duplications and deletions and their mechanisms of origin.

Duplications and deletions of the same gene loci or chromosome regions are known to produce different clinical manifestations and are significant factors in human morbidity and mortality. Extensive cytogenetic and molecular cytogenetic studies with cosmid and YAC probes in two patients with unique mosaicism for reciprocal duplication-deletion allowed us to further understand the origin of these abnormalities. The first patient's mosaic karyotype was 46,XX, inv dup(11) (q23q13)/46,XX,del(11)(q13q23).

Prenatal diagnosis of a mosaic extra structurally abnormal chromosome by spectral karyotyping.

A de novo mosaic extra structurally abnormal chromosome (ESAC) was detected in 33 per cent of cultured amniotic fluid cells from a pregnant woman. Neither Q-banding nor fluorescence in situ hybridization (FISH) employing a DNA probe for nucleolar organizer region demonstrated the presence of satellites on the ESAC. Spectral karyotyping (SKY) was performed in this prenatal case and led to a quick and accurate determination of the ESAC as chromosome 14 in origin.

Characterization of two extreme variants involving the short arm of chromosome 22: are they identical?

The heteromorphic nature of the short-arms of human acrocentric chromosomes is considered the norm without any dire consequences. We characterized two highly unusual chromosome 22 variants with extremely enlarged short arms by routine and molecular cytogenetic techniques. Routine banding revealed that the two variants were not alike.

Free beta hCG screening of hydropic and non-hydropic Turner syndrome pregnancies.

Fourteen cases of Turner syndrome (45,X), two cases of mosaic Turner syndrome (45,X/47,XXX and 45,X/ 46,XX), and one case of Turner syndrome involving an isochromosome X [46,X,i(X)(q10)] were ascertained by prenatal maternal serum alpha-fetoprotein (MSAFP) and free beta human chorionic gonadotropin (hCG) screening or by ultrasound. Patient-specific risks for Down syndrome were calculated and used as the criteria to determine offering further testing. Eleven of the 17 cases had hydrops and presented with an increased Down syndrome risk based on MSAFP and free beta hCG screening.