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1q21.1 deletion syndrome or 1q21.1 (recurrent) microdeletion is a rare aberration of chromosome 1. A human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 deletion syndrome, one chromosome of the pair is not complete, because a part of the sequence of the chromosome is missing. One chromosome has the normal length and the other is too short. 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 deletion is situated. The syndrome is a form of the 1q21.1 copy number variations and it is a deletion in the distal area of the 1q21.1 part. 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. 1q21.1 microdeletion is a very rare chromosomal condition. Only 46 individuals with this deletion have been reported in medical literature as of August 2011. ==Cause of the syndrome== Meiosis is the process of dividing cells in humans. In meiosis, the chromosome pairs split 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. A problem of the second random process is that genetic mistakes can occur. Because of 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 so-called 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, the result will be a 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, in sports or science. In negative cases, you have to deal with a syndrome or a severe disability, as in this case the 1q21.1 deletion syndrome. Based on the meiotic process, the syndrome may occur in two ways. # a spontaneous deviation (a 'de novo' situation): two chromosomes come together of which one has a copy number variation as a result of the meiosis process. # a parent is unknowingly the carrier of a chromosome with a copy number variation and passes it 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 deletion syndrome」の詳細全文を読む スポンサード リンク
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