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はじめに
脳アミロイドアンギオパチー(cerebral amyloid angiopathy: CAA)は,脳血管へのアミロイド沈着症である。現在までに,脳血管に沈着するアミロイド蛋白としてアミロイドβ蛋白(Aβ),シスタチンC(シスタチンC関連アミロイド:ACys),プリオン蛋白(PrP)(PrP関連アミロイド:AScr),トランスサイレチン(TTR)(TTR関連アミロイド:ATTR),ゲルゾリン(ゲルゾリン関連アミロイド:AGel),ABri/ADanの6種類が知られており,それに基づく分類がなされている(Table1)1)。
軽度のCAAは臨床症状と直接は関連しないが,高度のCAAは脳血管障害(脳出血,白質脳症,脳血管性認知症など)の原因となる1)。遺伝性のCAAに関しては後述するごとく遺伝子診断が可能であるが,最も多数を占める孤発性Aβ型CAAでは,遺伝子変異は通常検出されず2),診断に有用なマーカーは確立していない。しかし,近年いくつかの遺伝的な危険因子の関与が報告されており,今後の診断および治療に有用となる可能性がある。
本稿では,CAAに関して現在までに報告のある遺伝子多型や変異を,孤発性Aβ型CAAと遺伝性のCAAに分けて概説する。
Abstract
Cerebral amyloid angiopathy (CAA) is cerebrovascular amyloid deposition and is related to stroke and dementia. CAA is classified into 6 types according to the biochemical properties of amyloid proteins,and among 6 types,the sporadic CAA of amyloid β protein (Aβ) type is most frequently found in elderly people or patients with Alzheimer's disease (AD). In sporadic CAA of the Aβ type,the ε4 allele of the apolipoprotein E gene is associated with increased vascular Aβ deposition,while the ε2 allele is associated with CAA-related intracerebral hemorrhage. We have also reported that the genetic polymorphisms of presenilin-1,neprilysin,transforming growth factor β-1,and α1-antichymotrypsin are associated with CAA. In the case of hereditary CAA of the Aβ type,mutations in the genes of amyloid precursor protein (APP) and presenilins have been reported. Interestingly,the missense mutations associated with CAA are located in the middle portion of Aβ,while those associated with familial AD (FAD) are near the N- or C- terminals of Aβ. Individuals with FAD with APP duplication have been reported to present with severe CAA. Some of the FAD patients with mutations in the presenilin genes and patients with Down syndrome also show CAA as a complication. Besides sporadic or hereditary CAA of the Aβ type,hereditary CAA with cerebrovascular deposition of cystatin C,transthyretin,gelsolin,prion protein,and ABri/ADan have also been reported in association with mutations in the genes of the precursor proteins. Better understanding of the genetic factors influencing CAA will lead to identification of novel diagnostic markers and the development of preventive for CAA and CAA-related disorders.
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