X-LINKED PYRIDOXINE-RESPONSIVE SIDEROBLASTIC ANEMIA DUE TO A THR(388)-TO-SER SUBSTITUTION IN ERYTHROID 5-AMINOLEVULINATE SYNTHASE
X-LINKED PYRIDOXINE-RESPONSIVE SIDEROBLASTIC ANEMIA DUE TO A THR(388)-TO-SER SUBSTITUTION IN ERYTHROID 5-AMINOLEVULINATE SYNTHASE
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DOI：
10.1056/nejm199403103301004
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发表时间：
1994-03-10
影响因子：
158.5
通讯作者：
MAY, BK
中科院分区：
文献类型：
--
作者：
COX, TC;BOTTOMLEY, SS;MAY, BK
背景。 X连锁铁粒幼细胞性贫血通常与红系细胞中5-氨基乙酰丙酸合酶活性降低有关，某些病例对吡哆醇（该酶辅因子的前体）治疗有反应。最近发现的红细胞特异性 5-氨基乙酰丙酸合酶同工酶基因及其在 X 染色体上的定位使得该基因中的一个或多个缺陷很可能是贫血的根源。方法。利用红系 5-氨基乙酰丙酸合酶基因中的多态性二核苷酸重复序列，我们证实了该基因与 X 连锁吡哆醇反应性铁粒幼细胞贫血家族中的疾病之间的联系。因此，我们通过分析酶促扩增的 DNA 来寻找红系 5-氨基乙酰丙酸合酶基因中核苷酸序列异常的证据。结果。对亲属中两名受影响的男性和一名女性携带者进行的 DNA 测序研究表明，第 1215 号核苷酸（外显子 8）处的胞嘧啶变为鸟嘌呤。这种变化导致氨基酸残基 388 处的苏氨酸被丝氨酸取代，该残基靠近与磷酸吡哆醛辅因子结合的赖氨酸。在表达研究中，突变酶的活性相对于野生型有所降低，这种降低与先证者贫血复发期间红细胞中的活性相当。在吡哆醇存在下表达的酶活性与先证者缓解期间骨髓细胞中表达的酶活性相当。尽管突变酶对磷酸吡哆醛的亲和力没有改变，但突变似乎在酶的活性位点引入了构象变化。结论。我们发现，导致红系 5-氨基乙酰丙酸合酶同工酶的磷酸吡哆醛结合位点附近氨基酸变化的点突变是 X 连锁吡哆醇反应性铁粒幼细胞贫血家族的潜在缺陷。
Background. X-linked sideroblastic anemia is usually associated with reduced 5-aminolevulinate synthase activity in erythroid cells, and some cases are responsive to treatment with pyridoxine, the precursor to the cofactor of the enzyme. The recently identified gene for an erythroid-specific 5-aminolevulinate synthase isoenzyme and its localization to the X chromosome make it likely that one or more defects in this gene underlie the anemia. Methods. Using a polymorphic dinucleotide-repeat sequence in the erythroid 5-aminolevulinate synthase gene, we confirmed the linkage of this gene to the disorder in a family with X-linked pyridoxine-responsive sideroblastic anemia. We therefore sought evidence of a nucleotide-sequence abnormality in the erythroid 5-aminolevulinate synthase gene by analyzing enzymatically amplified DNA. Results. DNA-sequencing studies in two affected males and one carrier female in the kindred demonstrated a cytosine-to-guanine change at nucleotide 1215 (in exon 8). This change results in the substitution of serine for threonine at amino acid residue 388, near the lysine that binds the pyridoxal phosphate cofactor. In expression studies, the activity of the mutant enzyme was reduced relative to that of the wild type, and this reduction was comparable to that in erythroid cells of the proband during relapse of the anemia; the enzyme activity expressed in the presence of pyridoxine was comparable to that in the proband's marrow cells during remission. Although the affinity of the mutant enzyme for pyridoxal phosphate was not altered, the mutation appears to introduce a conformational change at the active site of the enzyme. Conclusions. We identified a point mutation resulting in an amino acid change near the pyridoxal phosphate-binding site of the erythroid 5-aminolevulinate synthase isoenzyme as the underlying defect in a kindred with X-linked pyridoxine-responsive sideroblastic anemia.