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Adenosine deaminase deficiency, also called ADA deficiency or ADA-SCID, is an autosomal recessive metabolic disorder that causes immunodeficiency. It occurs in fewer than one in 100,000 live births worldwide. It accounts for about 15% of all cases of severe combined immunodeficiency (SCID). Only 3% of children are born with this gene. ADA deficiency may be present in infancy, childhood, adolescence, or adulthood.〔 Age of onset and severity is related to some 29 known genotypes associated with the disorder. ==Pathophysiology== ADA deficiency is due to a lack of the enzyme adenosine deaminase. This deficiency results in an accumulation of deoxyadenosine, which, in turn, leads to: *a buildup of dATP in all cells, which inhibits ribonucleotide reductase and prevents DNA synthesis, so cells are unable to divide. Since developing T cells and B cells are some of the most mitotically active cells, they are highly susceptible to this condition. *an increase in S-adenosylhomocysteine since the enzyme adenosine deaminase is important in the purine salvage pathway; both substances are toxic to immature lymphocytes, which thus fail to mature. Because T cells undergo proliferation and development in the thymus, affected individuals typically have a small, underdeveloped thymus.〔p347, ''The Immune System'' Peter Parham, Garland Science, London and New York, 2009〕 As a result, the immune system is severely compromised or completely lacking. 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「adenosine deaminase deficiency」の詳細全文を読む スポンサード リンク
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