由于红系5-氨基酮戊酸合酶中苏氨酸388被丝氨酸取代导致的X连锁吡哆醇反应性铁粒幼细胞贫血。
X-linked pyridoxine-responsive sideroblastic anemia due to a Thr388-to-Ser substitution in erythroid 5-aminolevulinate synthase.
作者信息
Cox T C, Bottomley S S, Wiley J S, Bawden M J, Matthews C S, May B K
机构信息
Department of Biochemistry, University of Adelaide, Australia.
出版信息
N Engl J Med. 1994 Mar 10;330(10):675-9. doi: 10.1056/NEJM199403103301004.
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.
背景
X连锁铁粒幼细胞贫血通常与红系细胞中5-氨基酮戊酸合酶活性降低有关，部分病例对维生素B6（该酶辅因子的前体）治疗有反应。最近鉴定出的红系特异性5-氨基酮戊酸合酶同工酶基因及其在X染色体上的定位表明，该基因的一个或多个缺陷可能是贫血的基础。
方法
利用红系5-氨基酮戊酸合酶基因中的一个多态性二核苷酸重复序列，我们在一个患有X连锁维生素B6反应性铁粒幼细胞贫血的家族中证实了该基因与该疾病的连锁关系。因此，我们通过分析酶促扩增的DNA来寻找红系5-氨基酮戊酸合酶基因中核苷酸序列异常的证据。
结果
对该家族中两名患病男性和一名携带者女性的DNA测序研究表明，第1215位核苷酸（外显子8）发生了胞嘧啶到鸟嘌呤的变化。这种变化导致氨基酸残基388处的苏氨酸被丝氨酸取代，该位置靠近结合磷酸吡哆醛辅因子的赖氨酸。在表达研究中，突变酶的活性相对于野生型降低，这种降低与先证者贫血复发时红系细胞中的降低相当；在维生素B6存在的情况下表达的酶活性与先证者缓解期骨髓细胞中的活性相当。虽然突变酶对磷酸吡哆醛的亲和力没有改变，但该突变似乎在酶的活性位点引入了构象变化。
结论
我们鉴定出一个点突变，该突变导致红系5-氨基酮戊酸合酶同工酶的磷酸吡哆醛结合位点附近的氨基酸发生变化，这是一个患有X连锁维生素B6反应性铁粒幼细胞贫血家族的潜在缺陷。
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