Molecular Investigations of Duplications of Chromosome 15 in Autism
N. Carolyn Schanen, M.D., Ph.D.
Head of Human Genetics Research, Nemours Research Programs
Alfred I DuPont Hospital for Children, Wilmington DE
Phone: (302) 651-6702
Fax: (302) 651-6767
E-mail: schanen@medsci.udel.edu
Our research study on Molecular Investigations of Duplications of Chromosome 15 in Autism is recruiting new participants in this study through 2008. Most families who enroll after March 1, 2004 will only be asked to participate in the DNA study.
Numerous reports have implicated maternally derived rearrangements of proximal chromosome 15q as significant risk factors for autism and autism related disorders. The region undergoes gametic imprinting and thus parent-of-origin specific gene expression. Whether it is dosage of a particular interval or gene, or even involvement of a particular breakpoint that leads to the phenotype is unclear at present. As part of a NIH-funded program project, we are currently studying the molecular characteristics of chromosome 15 duplications in a large patient cohort to delineate the relationship between these duplications and the clinical presentation.
We are using of a combination of standard molecular, cytogenetic and microarray approaches to characterize the duplication regions. Roughly half of the duplication events arise due to the presence of a supernumerary marker chromosome while the remaining are interstitial duplications of the long arm. Once the smallest region of overlap has been defined, we will use resources of the human genome mapping project to identify candidate genes within this region.
We are learning a lot about the structural features of the long arm of chromosome 15 that predisposes it to rearrange and make duplication chromosomes. On chromosome 15, there are repeated regions that share nearly identical DNA sequence. Recent studies have determined that there are likely to be five main positions that are involved in the generation of duplication chromosomes. These repeated regions contain active genes, so understanding the positions that are involved in making the duplication chromosomes may help us understand the variability in the symptoms of people with duplications – the symptoms may depend on both what is duplicated and which repeat region was involved. Although the initial reports of idic(15) chromosomes suggested that the extra chromosome is symmetric and a mirror image, we have found that actually the positions of the breakpoints involved vary among kids with seemingly identical duplications (based on the clinical studies). How this affects outcome is not known at this point.
If any families would like more information or would like to enroll in our study,
Dup15q Alliance, P.O. Box 674, Fayetteville, NY 13066 USA
855-dup-15qa info@dup15q.org
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