Partial Monosomy 4p and Trisomy 12q due to a t(4;12)(p16.3;q24.31) Familial Translocation in Two Cousins.

Wolf-Hirschhorn syndrome (WHS) is caused by a distal 4p monosomy usually involving the region of the WHSC1 and WHSC2 genes. About 40-45% of WHS patients show an unbalanced translocation leading to both 4p monosomy and partial trisomy of another chromosome arm. In this case report, we describe 2 female cousins (P1 and P2) with a derivative chromosome leading to a 4p16.3pter deletion and 12q24.31qter duplication. Conventional karyotyping and genomic analyses showed that they both had the same rearrangement derived from a balanced parental translocation involving chromosomes 4 and 12, t(4;12)(p16.3;q24.31). The rearrangements occurred between 4p16.3pter and 12q24.31qter detected by array-CGH analysis, with a 2.7-Mb loss at 4p and a large 12.4-Mb gain at 12q. Both affected patients shared global developmental delay and craniofacial dysmorphisms with some distinct phenotypic findings associated with both WHS and 12qter trisomy. P2 was more severely impaired than P1, and she showed severe intellectual disability, seizures, midface hypoplasia, unilateral microtia, and deafness which were absent in P1. Previous studies of distal 4p monosomies have found phenotypic variability in WHS which does not correlate with haploinsufficiency of specific genes. Features of 12q trisomies are diverse with developmental and growth delay, intellectual disability, behavioral problems, and facial abnormalities. Collectively, our analysis of the literature of 3 similar translocations involving 4p and 12q, together with the clinical features of the affected cousins in this familial translocation, permits an evaluation of genes closely linked to WHSC1 and WHSC2 in the context of WHS and the genes involved in 12q trisomy.

Complex Mosaic Ring Chromosome 11 Associated with Hemizygous Loss of 8.6 Mb of 11q24.2qter in Atypical Jacobsen Syndrome.

Jacobsen syndrome (JBS) is a contiguous gene deletion syndrome involving terminal chromosome 11q. The haploinsufficiency of multiple genes contributes to the overall clinical phenotype, which can include the variant Paris-Trousseau syndrome, a transient thrombocytopenia related to FLI1 hemizygous deletion. We investigated a boy with features of JBS using classic cytogenetic methods, FISH and high-resolution array CGH. The proband was found to have a mosaic ring chromosome 11 resulting in a hemizygous 11q terminal deletion of 8.6 Mb, leading to a copy number loss of 52 genes. The patient had a hemizygous deletion in the FLI1 gene region without apparent thrombocytopenia, and he developed diabetes mellitus type I, which has not previously been described in the spectrum of disorders associated with JBS. The relationship of some of the genes within the context of the phenotype caused by a partial deletion of 11q has provided insights concerning the developmental anomalies presented in this patient with atypical features of JBS.