J. M. de Pater

MATERNAL UNIPARENTAL DISOMY FOR CHROMOSOME 22 IN A CHILD WITH GENERALIZED MOSAICISM FOR TRISOMY 22

We report on a case of generalized mosaicism for trisomy 22. At chorionic villus sampling (CVS) in the 37th week of pregnancy, a 47,XX,+22 karyotype was detected in all cells. The indication for CVS was severe unexplained symmetrical intrauterine growth retardation (IUGR) and a ventricular septal defect (VSD) was noted. In cultured cells from amniotic fluid taken simultaneously, only two out of ten clones were trisomic. At term, a growth‐retarded girl with mild dysmorphic features was born. Lymphocytes showed a normal 46,XX[50] karyotype; both chromosomes 22 were maternal in origin (maternal uniparental disomy). Investigation of the placenta post‐delivery using fluorescence in situ hybridization showed a low presence of trisomy 22 cells in only one out of 14 biopsies. In cultured fibroblasts of skin tissue, a mosaic 47,XX,+22[7]/46,XX[25] was observed. Clinical follow‐up is given up to 19 months.

Characterization of partial trisomy 9p due to insertional translocation by chromosomal (micro)FISH

de Pater JM, Ippel PF, van Dam WM, Loneus WH, Engelen JJM. Characterization of partial trisomy 9p due to insertional translocation by chromosomal (micro)FISH. 
Clin Genet 2002: 62: 482–487.

Isochromosome 1q as the Sole Chromosomal Abnormality in Two Fetal Teratomas: Possible Trisomic or Tetrasomic Zygote Rescue in Fetal Teratoma with an Additional Isochromosome 1q

An isochromosome of the long arm of chromosome 1 leading to tetrasomy 1q was detected as the sole chromosomal aberration in two cases of fetal teratoma arising from the oral cavity. This type of teratoma is extremely rare and has seldom been investigated cytogenetically. Studies of DNA markers in the tumor, normal fetal skin, and parental cells demonstrated that in both cases the additional 1q material was of maternal origin. In one of the patients, the teratoma had maternal 1q marker alleles that were not found in the fetal body cells. This implies that the tumor was not derived in a direct way from the fetal body tissue; instead, the chromosomally-normal fetus might be the result of some trisomic or tetrasomic zygote rescue mechanism.

Striking Facial Dysmorphisms and Restricted Thymic Development in a Fetus with a 6-Megabase Deletion of Chromosome 14q

During routine ultrasound screening at 12 weeks 5 days of gestation, a nuchal translucency of 7 mm, an omphalocele, and fetal hydrops were found and prompted chorionic villus sampling at 13 weeks 2 days. Chromosome analysis showed an unbalanced karyotype with an abnormal chromosome 14. The mother was a carrier of a translocation karyotype 46,XX,t(13;14) (q34;q32.2). In the fetus this gave rise to a partial trisomy 13q and partial monosomy 14q (fetal karyotype: 46,XX,der[14]t[13;14][q34;q32.2]). By Array-CGH on DNA extracted from a postmortem skin culture, a duplication of approximately 1.7 Mbp of the distal part of chromosome 13q34 and a deletion of approximately 6.0 Mbp of the distal part of chromosome 14q32.2 was demonstrated. Postmortem findings after termination of pregnancy at 14 weeks 6 days included, among others, a severe hypoplasia of the median part of the maxilla, no recognizable nose, a broad median palatoschisis, nonlobulated lungs, a horseshoe kidney with multicystic dysplasia, and decreased development of cortical cellularity in the thymus. These clinical manifestations and autopsy findings of the fetus are compared with those of previously published cases and the possible involvement in this pathology of the YY1 and JAG2 transcription factors and the BCL11b and SIVA-1 regulators of thymic development is discussed.

Unique mosaicism of structural chromosomal rearrangement: is chromosome 18 preferentially involved?

The mentally normal mother of a 4‐year‐old boy with del(18)(q21.3) syndrome was tested cytogenetically to study the possibility of an inherited structural rearrangement of chromosome 18. She was found to carry an unusual mosaicism involving chromosomes 18 and 21. Two unbalanced cell lines were seen as derivatives of a reciprocal translocation t(18;21), resulting in mosaicism of two cell lines, one with partial monosomy 18q and one with partial trisomy 18q. A literature review revealed that mosaicism of two or more cell lines with different unbalanced structural aberrations is extremely rare; moreover, chromosome 18 appeared to be involved in the majority of cases. We discuss possible mechanisms for the origin of this distinctive chromosomal constitution.