Diagnosis of a complex chromosomal rearrangement using fluorescent in situ hybridisation

Molecular cytogenetic analysis of complex chromosomal rearrangements in patients with mental retardation and congenital malformations: delineation of 7q21.11 breakpoints

Constitutional de novo complex chromosomal rearrangements (CCRs) are a rare finding in patients with mild to severe mental retardation. CCRs pose a challenge to the clinical cytogeneticist: generally CCRs are assumed to be the cause of the observed phenotypic abnormalities, but the complex nature of these chromosomal changes often hamper the accurate delineation of the chromosomal breakpoints and the identification of possible imbalances. In a first step towards a more detailed molecular cytogenetic characterization of CCRs, we studied four de novo CCRs using multicolor fluorescent in situ hybridization (M-FISH), comparative genomic hybridization (CGH), and FISH with region specific probes. These methods allowed a more refined characterization of the breakpoints in three of the four CCRs. The occurrence of 7q breakpoints in three out of these four CCRs and in 30% of reported CCRs suggested preferential involvement of this chromosomal region in the formation of CCRs. Further analysis of these 7q breakpoints revealed a 2 Mb deletion at 7q21.11 in one patient and involvement of the same region in a cryptic insertion in a second patient. This particular region contains at least 5 candidate genes for mental retardation. The other patient had a breakpoint more proximal to this region. The present data together with these from the literature provide evidence that a region within 7q21.11 may be prone to breakage and formation of CCRs.

Severe mental retardation-distal arthrogryposis in the upper limbs and complex chromosomal rearrangements resulting from a 10q25-->qter deletion

We present the first report of chromosomal rearrangement involving chromosomes 4, 10 and 12. The proband was a 42-year-old woman with severe mental retardation and multiple congenital anomalies. The most striking physical anomalies were upper limb contractures resulting in distal arthrogryposis. As upper limb flexion contractures have been previously reported in individuals with partial distal 10q deletion, this sign should be considered as part of the clinical manifestations of 10q25-->qter monosomy.

A new approach to the elucidation of complex chromosome rearrangements illustrated by a case of Rieger syndrome

A patient with a complex chromosome rearrangement and unilateral Rieger syndrome is presented. This rearrangement involves four chromosomes and six breakpoints, one of which is at 4q25, the candidate region for Rieger syndrome. We discuss a novel approach to the elucidation of this case using a multiprobe fluorescence in situ hybridisation method to show rearrangements unpredictable from G banded analysis, and the clear and unambiguous presentation of the karyotype using computer generated colour ideograms.