The chromosome 22q11 region is susceptible to rearrangements that are associated with congenital anomaly disorders and malignant tumors. Three congenital anomaly disorders, cat-eye syndrome, der() syndrome and velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) are associated with tetrasomy, trisomy or monosomy, respectively, for part of chromosome 22q11. VCFS/DGS is the most common syndrome associated with 22q11 rearrangements. In order to determine whether there are particular regions on 22q11 that are prone to rearrangements, the deletion end-points in a large number of VCFS/DGS patients were defined by haplotype analysis. Most VCFS/DGS patients have a similar 3 Mb deletion, some have a nested distal deletion breakpoint resulting in a 1.5 Mb deletion and a few rare patients have unique deletions or translocations. The high prevalence of the disorder in the population and the fact that most cases occur sporadically suggest that sequences at or near the breakpoints confer susceptibility to chromosome rearrangements. To investigate this hypothesis, we developed hamster-human somatic hybrid cell lines from VCFS/DGS patients with all three classes of deletions and we now show that the breakpoints occur within similar low copy repeats, termed LCR22s. To support this idea further, we identified a family that carries an interstitial duplication of the same 3 Mb region that is deleted in VCFS/DGS patients. We present models to explain how the LCR22s can mediate different homologous recombination events, thereby generating a number of rearrangements that are associated with congenital anomaly disorders. We identified five additional copies of the LCR22 on 22q11 that may mediate other rearrangements leading to disease.
"DS results from a 3-Mb deletion of chromosome 22q11 region spanning LCR22-A to LCR22-D. A minority of cases present either a common approximately 1.5-Mb nested deletion spanning LCR22-A to LCR22-B [Edelmann et al., 1999b]. Deletions distal to 22q11.21 have been reported. "
"The human 22q11.2 region is susceptible to chromosomal rearrangements because it contains low copy repeats (LCRs) [Edelmann et al., 1999; Babcock et al., 2003]. LCRs constitute $5% of the human genome and are 10–400 kb DNA blocks that show more than 95% identity between copies and can be responsible for genomic instability [Torres-Juan et al., 2007]. "
"Most recombination events occur between LCRs A and D, giving rise to the common 3 Mb deletion. Approximately 8% of patients have a 1.5 Mb deletion, nested within the 3 Mb deletion.20,54,56 It has been argued that the 1.5 Mb deletions contain all key genes responsible for the syndrome and, in particular, for the increased risk of psychiatric illness.5,57 "
[Show abstract][Hide abstract] ABSTRACT: The 22q11.2 deletion syndrome (22q11DS) is caused by an autosomal dominant microdeletion of chromosome 22 at the long arm (q) 11.2 band. The 22q11DS is among the most clinically variable syndromes, with more than 180 features related with the deletion, and is associated with an increased risk of psychiatric disorders, accounting for up to 1%-2% of schizophrenia cases. In recent years, several genes located on chromosome 22q11 have been linked to schizophrenia, including those encoding catechol-O-methyltransferase and proline dehydrogenase, and the interaction between these and other candidate genes in the deleted region is an important area of research. It has been suggested that haploinsufficiency of some genes within the 22q11.2 region may contribute to the characteristic psychiatric phenotype and cognitive functioning of schizophrenia. Moreover, an extensive literature on neuroimaging shows reductions of the volumes of both gray and white matter, and these findings suggest that this reduction may be predictive of increased risk of prodromal psychotic symptoms in 22q11DS patients. Experimental and standardized cognitive assessments alongside neuroimaging may be important to identify one or more endophenotypes of schizophrenia, as well as a predictive prodrome that can be preventively treated during childhood and adolescence. In this review, we summarize recent data about the 22q11DS, in particular those addressing the neuropsychiatric and cognitive phenotypes associated with the deletion, underlining the recent advances in the studies about the genetic architecture of the syndrome.
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