Prenatal diagnosis of 18p deletion and isochromosome 18q mosaicism in a fetus with a cystic hygroma.

Although, deletion of short arm of chromosome 18 is one of the most frequent autosomal terminal deletions, mosaic form of 18p deletion is infrequently observed. Furthermore, prenatally detected cases of 18p deletion and isochromosome 18q mosaicism are extremely rare. Herein, we present a case of del(18p)/i(18q) mosaicism, prenatally detected after chori- onic villus sampling. A 37-year-old woman was referred for prenatal diagnosis because of fetal septated cystic hygroma measuring 4.3 mm. Cytogenetic analysis showed a mosaic 46,XX,del(18)(p11.2)/46,XX,i(18)(q10) karyotype in both, short- and long-term culture. Parents elected to terminate the pregnancy. Fetal mosaic karyotype was confirmed by chromosomal analysis of cultured skin fibroblasts. Molecular characterization of chromosome 18 structural aberrations was performed by fluorescence in situ hybridization (FISH). Considering variable ultrasound findings among cases with del(18p)/i(18q) mosaicism, we emphasized that first and second trimester ultrasound screening examinations for fetal malformations, followed by cytogenetic and molecular evaluations, are very important in the management of prenatally detected cases.