15q24 deletion syndrome

Causes

Why is 15q24 microdeletion syndrome caused by a microdeletion?

15q24 microdeletion syndrome occurs when a person has one intact chromosome 15, but the other has a small amount of material missing (microdeletion) on the long arm (q). No single gene has so far been shown to produce the characteristic features of 15q24 microdeletion syndrome. The exact size of the deletion varies, but people with 15q24 are missing between 1.7 million and 6.1 million, or 1.7-6.1 megabases (Mb), of DNA building blocks (base pairs) at position q24 on chromosome 15. Base pairs are the chemicals in DNA that form the end of the "rungs" of its ladder-like structure.

Although the size of the deletion for 15q24 microdeletion varies with each individual (between 1.7-6.1 Mb), all individuals are missing the same 1.2 Mb region on one copy of their chromosome 15. The signs and symptoms that result from a 15q24 microdeletion are probably related to the loss of one or more genes in this deleted region, as this section on chromosome 15 contains several genes that are thought to be important for normal development. It is unclear, however, which missing genes contribute to the specific features of the disorder.

References
  • Genetics Home Reference. (2011). 15q24 microdeletion. Retrieved January 15, 2016, from http://ghr.nlm.nih.gov/condition/15q24-microdeletion
  • Unique. (2012). 15q24 microdeletion syndrome. Retrieved from http://www.rarechromo.org/information/Chromosome 15/15q24 microdeletion syndrome FTNW.pdf
  • Mefford H, Shur N, Rosenfeld J. 15q24 Microdeletion Syndrome. 2012 Feb 23. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016. Available from: http://www.ncbi.nlm.nih.gov/books/NBK84258/
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What gene change causes 15q24 microdeletion syndrome?

What gene change causes 15q24 microdeletion syndrome?

Chromosomes are made up mostly of DNA, and are the structures in the body's cells that carry genetic information (known as genes), which tell the body how to grow and develop. Each chromosome has a short (p) arm and a long (q) arm, and usually come in pairs, one from each parent. In addition to sex chromosomes, which are: XX (a pair of X chromosomes) in females and XY (one X chromosome and Y chromosome) in males, the remaining 44 chromosomes are grouped in 22 pairs and are numbered 1 to 22.

15q24 microdeletion syndrome occurs when a person has one intact chromosome 15, but the other has a small amount of material missing (microdeletion) on the long arm (q). No single gene has so far been shown to produce the characteristic features of 15q24 microdeletion syndrome. The exact size of the deletion varies, but people with 15q24 are missing between 1.7 million and 6.1 million, or 1.7-6.1 megabases (Mb), of DNA building blocks (base pairs) at position q24 on chromosome 15. Base pairs are the chemicals in DNA that form the end of the "rungs" of its ladder-like structure.

Determining the exact size of the deletion is necessary for identifying what genes may contribute to the features of 15q24 microdeletions. It has been noted that 1.1 Mb region in which 26 genes are located is deleted in the majority of cases so far, and has been deemed a critical region for 15q24 microdeletion syndrome. Children who have had small deletions that lie outside the more typical 1.1 Mb region, and involve a small number of genes (5-15), and had milder features of the syndrome with mild learning difficulties and reasonable speech.

References
  • Andrieux J, Dubourg C, Rio M, Attie-Bitach T, Delaby E, Mathieu M, Journel H, Copin H, Blondeel E, Doco-Fenzy M, Landais E, Delobel B, Odent S, Manouvrier-Hanu S, Holder-Espinasse M. Genotype-phenotype correlation in four 15q24 deleted patients identified by array-CGH. Am J Med Genet A. 2009;149A:2813?9
  • El-Hattab AW, Zhang F, Maxim R, Christensen KM, Ward JC, Hines-Dowell S, Scaglia F, Lupski JR, Cheung SW. Deletion and duplication of 15q24: molecular mechanisms and potential modification by additional copy number variants. Genet Med. 2010;12:573?86
  • Genetics Home Reference. (2011). 15q24 microdeletion. Retrieved January 15, 2016, from http://ghr.nlm.nih.gov/condition/15q24-microdeletion
  • Mefford H, Shur N, Rosenfeld J. 15q24 Microdeletion Syndrome. 2012 Feb 23. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016. Available from: http://www.ncbi.nlm.nih.gov/books/NBK84258/
  • Unique. (2012). 15q24 microdeletion syndrome. Retrieved from http://www.rarechromo.org/information/Chromosome 15/15q24 microdeletion syndrome FTNW.pdf

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