Chromosomal mosaicism was found in 38 of 4,000 chorionic villus samples examined from 1998 to 2003. A small fraction of these (5/38) were confirmed as true mosaics by analysis of amniotic fluid. Twenty-nine cases that fit the definition of confined placental mosaicism were followed with clinical and cytogenetic analysis throughout the pregnancy, at birth and in a few cases into infancy. This was done to determine the prognostic interpretation of prenatal cytogenetic results from multiple specimens in a single pregnancy and thus allow for reevaluation of the genetic counseling. In 2 of these 29 cases, low-level mosaicism was found in the neonate, and in 1 of these the chromosome abnormality is probably the cause of the resulting minor phenotypic abnormalities. Families face unique difficulties when confined placental mosaicism is the prenatal diagnosis, and it is extremely important that the counseling they receive takes into consideration the unlikely possibility of the placental abnormality appearing in fetal tissues.

Mosaic trisomy 8, also known as Warkany syndrome, has a well-characterized constellation of phenotypic findings. Partial trisomy 8, including mosaic cases, has also been reported, with outcome and counseling dependent on the chromosomal segment involved and whether accompanied by partial aneuploidy for other chromosomes. We present a case of a fetus mosaic for trisomy of the entire long arm (q) of chromosome 8 without additional chromosomal aberrations. The diagnosis was made by amniocentesis performed following an 18 week sonogram that showed multiple fetal anomalies. Mosaicism for trisomy 8q was confirmed by routine karyotyping and fluorescent in situ hybridization (FISH) analysis. The case proved useful for testing the sensitivity of array comparative genomic hybridization (array-CGH) with respect to segmental trisomy in the presence of chromosomal mosaicism. The phenotype of this fetus, which appears to be the first reported case involving mosaic trisomy 8 for the entire q arm of the chromosome, is described and compared to previously reported cases involving partial trisomy 8q.

Objectives: To explore the advantages and limitations of comparative genomic hybridization to BAC arrays (array CGH) for prenatal diagnosis of a fetus with anomalies and a chromosome abnormality. Methods: We used karyotype analysis, FISH and array CGH to investigate an unbalanced chromosome rearrangement. Results: We report a case of a fetus with ultrasound anomalies at 11 weeks’ gestation and an unbalanced chromosome translocation [46,XX,der(13)t(2;13)(p25.1;q32)pat]. Initially, a chromosome 13 deletion was reported from G-banded chromosome analysis and 13q subtelomere FISH. The involvement of chromosome 2 was determined after a balanced translocation was identified in the father, 46,XY,t(2;13)(p25.1;q32). Array CGH confirmed the fetal abnormality as partial trisomy of the short arm chromosome 2 and partial monosomy of the long arm of chromosome 13. The abnormalities identified by ultrasound studies and autopsy appear to be most consistent with 13q deletion syndrome. Conclusions: Array CGH successfully identified a subtle unbalanced chromosome complement in a fetus with multiple ultrasound anomalies. If array CGH had been performed along with the fetal karyotype, the cryptic partial trisomy 2 could have been identified in a more timely manner to assist in the prenatal counseling of this family.

The sensitivity of array CGH was valuable in detecting monosomy of the MLS critical region. Array CGH should be considered for the prenatal diagnosis of this syndrome.