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1q21.1 duplication syndrome or 1q21.1 (recurrent) microduplication is a rare aberration of chromosome 1. (Unique ), the international rare chromosome disorder group, has 57 genetically confirmed registered cases of this duplication worldwide (October 2012). In a common situation a human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 duplication syndrome one chromosome of the pair is over complete, because a part of the sequence of the chromosome is duplicated twice or more. In 1q21.1, the '1' stands for chromosome 1, the 'q' stands for the long arm of the chromosome and '21.1' stands for the part of the long arm in which the duplication is situated. Next to the duplication syndrome, there is also a 1q21.1 deletion syndrome. While there are two or three copies of a similar part of the DNA on a particular spot with the duplication syndrome, there is a part of the DNA missing with the deletion syndrome on the same spot. Literature refers to both the deletion and the duplication as the 1q21.1 copy-number variations (CNV). The CNV leads to a very variable phenotype and the manifestations in individuals are quite variable. Some people who have the syndrome can function in a normal way, while others have symptoms of mental retardation and various physical anomalies. ==Cause of the syndrome== Meiosis is the process of dividing cells in humans. In meiosis, the chromosome pairs splits and a representative of each pair goes to one daughter cell. In this way the number of chromosomes will be halved in each cell, while all the parts on the chromosome (genes) remain, after being randomized. Which information of the parent cell ends up in the daughter cell is purely decided by chance. Besides this random process, there is a second random process. In this second random process the DNA will be scrambled in a way that pieces are omitted (deletion), added (duplication), moved from one place to another (translocation) and inverted (inversion). This is a common process, which leads to about 0.4% variation in the DNA. It explains why even identical twins are not genetically 100% identical. The second random process can give rise to genetic mistakes. In the deletion and duplication process, the chromosomes that come together in a new cell may be shorter or longer. The result of this spontaneous change in the structure of DNA is a copy number variation. Due to the copy number variation chromosomes of different sizes can be combined in a new cell. If this occurs around conception, there is the first cell of a human with a genetic variation. This can be either positive or negative. In positive cases this new human will be capable of a special skill that is assessed positively, for example, sports or science. In negative cases, you have to deal with a syndrome or a severe disability, as in this case the 1q21.1 duplication syndrome. Based on the meiotic process, the syndrome may occur in two ways. *1. a spontaneous deviation (a 'novo' the situation): two chromosomes come together of which one has a copy number variation as a result of the meiosis process. *2. a parent is unknowingly carrier of a chromosome with a copy number variation and passes itthrough at conception to the child, with different consequences for the child. Due to this genetic misprint the embryo may experience problems in the development during the first months of pregnancy. Approximately 20 to 40 days after fertilization, something goes wrong in the construction of the body parts and brain, which leads to a chain reaction.〔A. Ploeger; 'Towards an integration of evolutionary psychology and developmental science: New insights from evolutionary developmental biology'〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「1q21.1 duplication syndrome」の詳細全文を読む スポンサード リンク
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