A complete study and understanding of Down syndrome from a genetic point of view

In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genescarry the codes responsible for all of our inherited traits and are grouped along rod-like structures calledchromosomes. Typically, the nucleus of each cell contains ۲۳ pairs of chromosomes, half of which areinherited from each parent. Down syndrome occurs when an individual has a full or partial extra copyof chromosome ۲۱. This additional genetic material alters the course of development and causes thecharacteristics associated with Down syndrome. A few of the common physical traits of Downsyndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep creaseacross the center of the palm – although each person with Down syndrome is a unique individual andmay possess these characteristics to different degrees, or not at all. For centuries, people with Downsyndrome have been alluded to in art, literature, and science. It wasn’t until the late nineteenth century,however, that John Langdon Down, an English physician, published an accurate description of a personwith Down syndrome. It was this scholarly work, published in ۱۸۶۶, that earned Down the recognitionas the “father” of the syndrome. Although other people had previously recognized the characteristics ofthe syndrome, it was Down who described the condition as a distinct and separate entity. In recenthistory, advances in medicine and science have enabled researchers to investigate the characteristics ofpeople with Down syndrome. In ۱۹۵۹, the French physician Jérôme Lejeune identified Down syndromeas a chromosomal condition. Instead of the usual ۴۶ chromosomes present in each cell, Lejeuneobserved ۴۷ in the cells of individuals with Down syndrome. It was later determined that an extra partialor whole copy of chromosome ۲۱ results in the characteristics associated with Down syndrome. In theyear ۲۰۰۰, an international team of scientists successfully identified and catalogued each of theapproximately ۳۲۹ genes on chromosome ۲۱. This accomplishment opened the door to great advancesin Down syndrome research. Down's syndrome is a genetic disorder that can lead to mental retardationof varying degrees. How this chromosomal abnormality causes mental retardation remains an openquestion. This paper res what is currently known about the neural and cognitive features of Down'ssyndrome, noting the growing evidence of disproportionate impairment of specific systems such as thehippocampal formation, the prefrontal cortex and the cerebellum. The development of animal modelsof these defects offers a way of ultimately connecting the genetic disorder to its cognitive consequences.

کلیدواژه ها:

DNA methylation ، Acetylation ، Tumor suppressor gene ، Tumor suppressive miRNA.