Mosaic Trisomy 12 Associated with Overgrowth Detected in Fibroblast Cell Lines.

Mosaic trisomy 12 is a rare anomaly, and only 9 cases of live births with this condition have been reported in the literature. The clinical phenotype is variable, including neuropsychomotor developmental delay, congenital heart disease, microcephaly, cutaneous spots, facial asymmetry, prominent ears, hypotonia, retinopathy, and sensorineural hearing loss. A 2-year-old female presented with neuropsychomotor developmental delay, prominent forehead, dolichocephaly, patchy skin pigmentation, and unexpected overgrowth at birth. Cytogenetic analysis of her peripheral blood showed normal results, suggesting the presence of a chromosomal alteration in other tissues. Further studies using G-banding and FISH performed on fibroblasts from both hyper- and hypopigmented regions identified a 47,XX,+12/46,XX karyotype. To the best of our knowledge, no patients with mosaic trisomy 12 associated with overgrowth have been reported to date. Congenital overgrowth and neonatal overgrowth have been frequently linked to Pallister-Killian syndrome (PKS; OMIM 601803). This case suggests the possibility of an association of genes present in the 12p region with fetal overgrowth, considering that chromosomal duplications could lead to an increase in the production of aberrant transcripts and disturbing gene dosage effects. This case highlights the importance of cytogenetic analysis in different tissues to provide relevant information to the specific genotype/phenotype correlation.

Subtelomeric Copy Number Variations: The Importance of 4p/4q Deletions in Patients with Congenital Anomalies and Developmental Disability.

The most prevalent structural variations in the human genome are copy number variations (CNVs), which appear predominantly in the subtelomeric regions. Variable sizes of 4p/4q CNVs have been associated with several different psychiatric findings and developmental disability (DD). We analyzed 105 patients with congenital anomalies (CA) and developmental and/or intellectual disabilities (DD/ID) using MLPA subtelomeric specific kits (P036 /P070) and 4 of them using microarrays. We found abnormal subtelomeric CNVs in 15 patients (14.3%), including 8 patients with subtelomeric deletions at 4p/4q (53.3%). Additional genomic changes were observed at 1p36, 2q37.3, 5p15.3, 5q35.3, 8p23.3, 13q11, 14q32.3, 15q11.2, and Xq28/Yq12. This indicates the prevalence of independent deletions at 4p/4q, involving PIGG, TRIML2, and FRG1. Furthermore, we identified 15 genes with changes in copy number that contribute to neurological development and/or function, among them CRMP1, SORCS2, SLC25A4, and HELT. Our results highlight the association of genes with changes in copy number at 4p and 4q subtelomeric regions and the DD phenotype. Cytogenomic characterization of additional cases with distal deletions should help clarifying the role of subtelomeric CNVs in neurological diseases.