text: ②腺苷脱氨酶（ADA）缺陷为ADA基因突变，ADA缺乏引起嘌呤旁路和甲基化旁路的中间代谢产物脱氧三磷酸腺苷（dATP）和S-腺苷同型半亮氨酸（S-adenosylhomocysteine）堆积，它们具有细胞毒效应，抑制T、B细胞增殖和分化。
entities.entity: 腺苷脱氨酶（ADA）缺陷
entities.label: dis
entities.entity: ADA
entities.label: bod
entities.entity: ADA缺乏
entities.label: dis
entities.entity: 嘌呤旁路
entities.label: bod
entities.entity: 甲基化旁路
entities.label: bod
entities.entity: 脱氧三磷酸腺苷
entities.label: bod
entities.entity: dATP
entities.label: bod
entities.entity: S-腺苷同型半亮氨酸
entities.label: bod
entities.entity: S-adenosylhomocysteine
entities.label: bod
entities.entity: 细胞
entities.label: bod
entities.entity: B细胞
entities.label: bod