Use of fluorescence in situ hybridization to confirm the interpretation of a balanced complex chromosome rearrangement ascertained through prenatal diagnosis

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.

Analysis of a familial three way translocation involving chromosomes 3q, 6q, and 15q by high resolution banding and fluorescent in situ hybridisation (FISH) shows two different unbalanced karyotypes in sibs

We report on a familial three way translocation involving chromosomes 3, 6, and 15 identified by prometaphase banding and fluorescence in situ hybridisation (FISH). Two mentally retarded sibs with different phenotypic abnormalities, their phenotypically normal sister and mother, and two fetuses of the phenotypically normal sister were analysed. The terminal regions of chromosomes 3q, 6q, and 15q were involved in a reciprocal translocation, in addition to a paracentric inversion of the derivative chromosome 15. Conventional cytogenetic studies with high resolution GTG banding did not resolve this rearrangement. FISH using whole chromosome paints (WCPs) identified the chromosomal regions involved, except the aberrant region of 3q, which was undetectable with these probes. Investigation of this region with the subtelomeric FISH probe D3S1445/D3S1446 showed a balanced karyotype, 46,XX,t(3;15;6) (q29;q26.1;q26), inv der(15) (q15.1q26.1) in two adult females and one fetus. It was unbalanced in two sibs, showing two different types of unbalanced translocation resulting in partial trisomy 3q in combination with partial monosomy 6q in one patient and partial trisomy 15q with partial monosomy 6q in the other patient and one fetus. These represent apparently new chromosomal phenotypes.

Familial four breakpoint complex chromosomal rearrangement as a cause of monosomy 9p22-->pter and trisomy 10p11.2-->pter and 11q21 analysed by dual and triple colour FISH

A familial four breakpoint complex chromosomal rearrangement involving chromosomes 9, 10, and 11 was ascertained through a child with dysmorphic features, hypertrophic cardiomyopathy, and hypotonia. A cryptic insertion, invisible in G banded chromosomes was identified by fluorescence in situ hybridisation (FISH) using chromosome specific libraries. Possible mechanisms of its formation as well as karyotype-phenotype correlation are discussed.

Diagnosis of a complex chromosomal rearrangement using fluorescent in situ hybridisation

We report the use of fluorescent in situ hybridisation (FISH) to clarify a complex chromosomal rearrangement (CCR) carried by a woman presenting with recurrent miscarriages. CCRs are rare cytogenetic rearrangements involving three or more chromosomes, which can be difficult to interpret using routine cytogenetic studies with GTG banding. FISH was used to establish a correct interpretation of the maternal karyotype before amniocentesis in a present pregnancy.

Prenatally diagnosed de novo apparently balanced complex chromosome rearrangements: two new cases and review of the literature

Complex chromosome rearrangements (CCR) are rare structural rearrangements. Currently six cases of prenatally diagnosed balanced de novo CCR have been described. We present two new cases of prenatally ascertained balanced de novo CCR. In the first case, an amniocentesis revealed a balanced de novo three-way CCR involving chromosomes 5, 6, and 11 with a pericentric inversion of chromosome 5 [four breaks]. In the second case, a balanced de novo rearrangement was identified by amniocentesis which involved a reciprocal translocation between chromosomes 3 and 8 and a CCR involving chromosomes 6, 7, and 18 [six breaks]. The use of whole chromosome painting helped elucidate the nature of these rearrangements. A review of the postnatally ascertained cases suggests that most patients have congenital anomalies, minor anomalies, and/or developmental delay/mental retardation. In addition, there appears to be a relationship between the number of chromosome breaks and the extent of phenotypic effects. The paucity of information regarding prenatally diagnosed CCR and the bias of ascertainment of postnatal CCR cases poses a problem in counseling families.

Complex chromosomal rearrangements: some breakpoints may have cellular adaptive significance

Cytogenetic study of a 3-year-old girl with developmental delay and some minor abnormalities revealed a complex chromosome rearrangement (CCR) involving seven chromosomes with eight breakpoints, leading to monosomy of segment 5q15-q22. According to breakpoint distribution, CCRs may be classified as those with primary intrachromosomal abnormalities (including inversions, insertions, duplications, etc.) and those without them. Only the latter group of CCRs was used in this analysis. Comparison of theoretical and observed breakpoint distributions in 33 cases demonstrated that recurrent involvement of some chromosome(s) ("re-entry") occurs more frequently than expected. One possible explanation for this observation suggests that the initial event leads to an unstable provisional rearrangement, and subsequent breaks are necessary to stabilize the karyotype.