Mosaic Trisomy 21/Monosomy 21 in a Living Female Infant

Abstract

Many autosomal monosomies are presumed to end in arrested growth in the first few mitoses, prior even to the time of implantation, with possibly some proceeding to the stage of occult abortion. The single exception may be monosomy 21, although this has been questioned, with most earlier reports of monosomy 21 recently re-interpreted as being due to an unbalanced translocation involving chromosome 21. Here we report a female infant with a mosaic trisomy 21/monosomy 21 karyotype. While the karyotype 46,XX,i(21)(q10) is detected in all metaphases investigated in lymphocytes, mosaicism with the karyotype 46,XX,i(21)(q10)[31]/45,XX, –21[12] is seen in fibroblasts from a skin biopsy. Dysmorphic facial features and multiple malformations remarkably resemble cases of monosomy 21 that have been described in the literature. This suggests a dominant phenotypic effect of loss of one chromosome 21. Detailed clinical description, results of gene dosage studies, and cytogenetic analysis will be presented.

Mental retardation, congenital heart malformation, and myelodysplasia in a patient with a complex chromosomal rearrangement involving the critical region 21q22

“…The current patient shares with the phenotype of patients carrying 21q monosomy the presence of mental retardation, downslanting palpebral fissures, downturned corners of mouth, micrognathia, heart defect, hematologic disorders. Two previous patients [Barbi et al, 2000;Nguyen, 2009], with a combi-nation of monosomy and trisomy of 21q, though involving regions different from those of our patient, have been described. The authors suggested a dominant role of monosomy in defining the clinical phenotype.…”

De novo MECP2 duplication in two females with random X-inactivation and moderate mental retardation

“…Besides genotyping, we measured peak heights for all duplication carriers compared with normal controls in order to identify duplicated and nonduplicated alleles as described previously. 15 The SNP-microarray data were evaluated considering the genotype and the corresponding probe signals within the duplicated region, thus providing a correlation of a specific genotype and the respective signal height. The origin of the duplication was identified by an allele-specific elevation of signal intensity in the patient in comparison with the parental genotypes.…”

Constitutional and Acquired Autosomal Aneuploidy

“…In addition to mosaicism involving autosomal trisomy, patients having mosaicism for autosomal monosomy have also been described, including mosaic monosomies for chromosomes 13 [ 62 ], 21 [ 70,72 ], and 22 [ 4 ] (Table 2). However, these conditions are too rare to allow for the establishment of a distinct syndromic phenotype.…”