Trisomy 21 with 47,+18 lymphocyte cell line: double mitotic nondisjunction

Double aneuploidy mosaicism involving chromosomes 18 and 21 in a neonate

BACKGROUND

Double aneuploidy is common, especially in products of conception, frequently involving a combination of a sex chromosome and an acrocentric chromosome. Double autosomal trisomies are rare with only five cases reported. Double aneuploidy mosaicism involving two different cell lines is rarer with only three cases reported.

CASE PRESENTATION

We report a fourth case of double aneuploidy mosaicism on a baby. Results of a 24-h preliminary chromosome analysis at birth showed a mosaic karyotype, 47,XX,+18[15]/47,XX,+21[8]/48,XX,+21,+mar[7]. Reflex testing to SNP microarray with the same sample collected at birth showed gain of a 77.9 Mb region on chromosome 18 and gain of a 32.5 Mb region on chromosome 21. Microarray did not show any other copy number variants indicating that the marker chromosome may not contain any euchromatic material. A repeat chromosome analysis at 1-year of age showed a mosaic karyotype, 47,XX,+18[76]/47,XX,+21[4] with loss of the marker cell line.

CONCLUSION

Based on our results, we propose that the mosaic double autosomal trisomy in our case was due to two independent non-disjunction events in a normal zygote very early during embryogenesis.

Trisomy 13/trisomy 18 mosaicism in an infant

Cytogenetic analysis of amniotic fluid cells from a 31-week-old fetus suffering from polyhydramnios revealed that there were two cell lines, each with either trisomy 13 or trisomy 18. We studied the origin and mechanism for formation of this unique mixoploidy by tracing chromosomal heteromorphisms as genetic markers, and showed no discordance of parent-child transmission between the two cell lines in any of the heteromorphisms examined. The result indicated that the mixoploidy is not chimerism but mosaicism and that the mechanism of mosaic development is most likely due to two non-disjunctional events which had occurred independently at the two-cell stage of the zygote. A girl was born at the 38th gestational week and her clinical features were mainly those for trisomy 13. Chromosome analysis of the newborn confirmed +13/+18 mosaicism in fibroblasts from the skin and chorionic plate, while cord blood lymphocytes and chorionic villus cells showed only the +18 cell line.

Trisomy 18 and trisomy 21 mosaicism in a Down's syndrome patient

A male child with typical features of Down's syndrome and mosaicism of two trisomic cell lines, trisomy 18 (84%) and trisomy 21 (16%), is reported. Non-disjunction or anaphase lag of chromosomes 18 and 21 could be the cause.

Trisomy 18/trisomy 13 mosaicism in an adult with profound mental retardation and multiple malformations

We report on an adult woman with profound mental retardation and multiple anomalies who consists of 3 cell lines: one with trisomy 18, one with trisomy 13, and a normal cell line. Her phenotype includes manifestations of both trisomy syndromes. The origin of these cell lines could have been a doubly aneuploid (48,XX + 13, + 18) or singly aneuploid (47,XX + 18 or 47,XX + 13) zygote with subsequent mitotic nondisjunctions, or a normal zygote with multiple mitotic nondisjunctions. There have been four previous reports of mosaicism involving both trisomy D and trisomy E; all died in the first six months of life. Two of these cases had a doubly aneuploid (48,XX, + D + E) cell line. Our patient illustrates the need for study of several tissues in patients with complex aneuploidy syndromes or atypical manifestations of a given syndrome (such as prolonged survival), as well as the need for caution in counseling families about prognosis for survival in autosomal trisomies which usually are lethal.