Severe psychomotor retardation in a boy with a small supernumerary marker chromosome 19p

Molecular cytogenetics characterization of seven small supernumerary marker chromosomes derived from chromosome 19: Genotype-phenotype correlation and review of the literature

Only a few subjects carrying supernumerary marker chromosomes derived from 19 chromosome (sSMC(19)) have been described to date and for a small portion of them the genic content has been defined at the molecular level. We present seven new different sSMCs(19) identified in eight individuals, seven of whom unrelated. The presence of the sSMC is associated with a clinical phenotype in five subjects, while the other three carriers, two of whom related, are normal. All sSMCs(19) have been characterized by means of conventional and molecular cytogenetics. We compare the sSMCs(19) carriers with a clinical phenotype to already described patients with gains (sSMCs or microduplications) of overlapping genomic regions with the aim to deepen the pathogenicity of the encountered imbalances and to assess the role of the involved genes on the phenotype. The present work supports the correlation between the gain of some chromosome 19 critical regions and specific phenotypes.

A systematic analysis of small supernumerary marker chromosomes using array CGH exposes unexpected complexity

PURPOSE

A small supernumerary marker chromosome is often seen in patients with developmental disorders. Prior to array-based comparative genomic hybridization markers were rarely genotyped end to end. In this study, a valid genotype-to-phenotype correlation was possible because the supernumerary marker chromosomes were fully characterized by array-based comparative genomic hybridization in a genome-wide analysis.

METHODS

Ten consecutive de novo small supernumerary marker chromosome cases were systematically genotyped using G-banding, C-banding, AgNOR staining, whole-genome array-based comparative genomic hybridization, and fluorescence in situ hybridization.

RESULTS

Among 10 small supernumerary marker chromosome cases studied, 4 (40%) were not identified by array-based comparative genomic hybridization because of low-level mosaicism or because they lacked euchromatin. One case (10%) was a simple pericentromeric marker extending from 5p13.3 to 5q11.2. Five (50%) markers showed unexpected complexity. Two cases had markers that were derivative acrocentric (AgNOR+) chromosomes with the euchromatin from chromosomes 18p or 19p. Each of the other three cases with complex markers had unusual characteristics including a marker from noncontiguous segments of chromosome 19q, a highly complex rearrangement involving a chromosome 20 homolog as well as the small supernumerary marker chromosome, and a mosaic duplication of a proximal 8p marker.

CONCLUSION

Small supernumerary marker chromosomes are frequently complex on the basis of our small sample. Whole-genome array-based comparative genomic hybridization characterization of the small supernumerary marker chromosome provided informed genetic counseling.

Identification and characterization of a complex pure mosaic of small supernumerary marker chromosomes involving 11p11.12 → q12.1 and 19p12 → q12 regions in a child featuring multiple congenital anomalies

Unstable, gene-rich pericentric regions have been associated with various structural aberrations including small supernumerary marker chromosomes (sSMCs). We hereby report on a complex pure mosaic sSMCs derived from chromosomes 11 and 19 in a child featuring multiple congenital anomalies. As indicated by microarray analysis, the sSMCs have involved materials from 11p11.12 → q12.1 and 19p12 → q12 in complex forms (with four cell lines harboring from 1 to 4 sSMCs) in all peripheral blood lymphocytes. The patient featured facial dysmorphism, generalized hypotonia, cryptorchidism, transverse palmar creases, cerebral hemorrhage, atrial septal defect secundum, strabismus, epilepsy, immunodeficiency, and severe cognitive and motor impairment. Literature review indicated this to be a unique sSMCs case simultaneously involving chromosomes 11 and 19, with one sSMC containing materials from the both chromosomes. We propose that the involved chromosomal regions may contain dosage-sensitive genes which are important for the development, and that the sSMCs derived from multiple origins have formed by a complex mechanism.