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9q34 deletion syndrome
9q34 deletion syndrome, also known as Kleefstra syndrome, is a rare genetic disorder. Terminal deletions of chromosome 9q34 have been associated with childhood hypotonia, a distinctive facial appearance and developmental disability. The facial features typically described include arched eyebrows, small head circumference, midface hypoplasia, prominent jaw and a pouting lower lip. Individuals with this disease may often have speech impediments, such as speech delays. Other characteristics of this disease include: epilepsy, congenital and urogenetic defects, microcephaly, corpulence, and psychiatric disorders.〔Berry Kravis, E.M., et al., Update on Kleefstra Syndrome. Molecular Syndromology. 2012 Jan;2:202-211.〕 From analysis of chromosomal breakpoints, as well as gene sequencing in suggestive cases, Kleefstra and colleagues identified EHMT1 as the causative gene.〔Kleefstra et al., Disruption of the gene Euchromatin Histone Methyl Transferase1 (Eu-HMTase1) is associated with the 9q34 subtelomeric deletion syndrome. J Med Genet. 2005 Apr;42(4):299-306.〕 This gene is responsible for producing the protein Histone methyltransferase which functions to alter histones. Ultimately, histone methyltransferases are important in deactivating certain genes, needed for proper growth and development. Moreover, a frameshift, missense, or nonsense error in the coding sequence of EHMT1 can result in this condition in an individual.
==History and etiology==
Kleefstra syndrome is a new condition that has only been known about for a few years and there have been fewer than 200 cases, reported. Due to the lack of cases worldwide, however, the history behind the origination is unclear.〔Author, A. A., & Author, B. B. (29 December 2012). What is Kleefstra Syndrome. Retrieved from ()〕 Despite the associated effects of Kleefstra, there is insubstantial information regarding to the lethality of Kleefstra's. Most the of the documented cases are de novo with the exception of one case due to hereditary factors; however, some cases may be a result of chromosomal translocations. In the exception case, the mother transferred the EHMT1 point mutation on to her child as she was a carrier of this gene defect. According to Mitter, et al. (2012), the mother's phenotype of the NM_024757.4:c.2712+1G>A mutation displayed mosaicism at certain tissues. This mutation resulted in the disregard of exon 18 on the EHMT1 gene, as opposed to removing it through the spliceosomes. In another transcript, however, an intron was placed between exon 18 and 19 of the EHMT1 gene. The combination of the intron insertion and the mosaicism in the mother was transferred to the child, resulting in the pathogenesis of the disease.〔Mitter, D., et al. ("A mosaic maternal splice donor mutation in the EHMT1 gene leads to aberrant transcripts and to Kleefstra syndrome in the offspring." ), ''European Journal of Human Genetics'', 2012 December 12〕
In the past, research showed that the austerity of the disease was directly proportional to the number of EHMT1 deletions prevalent in an individual. The greater the deletions, the greater the severity of the condition. However, in recent studies, 9q34 deletion syndrome occurs when the EHMT1 gene is non-functioning, as opposed to strictly deletion.〔Rare Chromosome Disorder Support Group, ("Kleefstra Syndrome" ), ''Kleefstra Syndrome'', 2009〕
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