Kitanaka S, Takeyama K, Murayama A, Sato T, Okumura K, Nogami M, Hasegawa Y, Niimi H, Yanagisawa J, Tanaka T, Kato S
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
N Engl J Med. 1998 Mar 5;338(10):653-61. doi: 10.1056/NEJM199803053381004.
Pseudovitamin D-deficiency rickets is characterized by the early onset of rickets with hypocalcemia and is thought to be caused by a deficit in renal 25-hydroxyvitamin D3 1alpha-hydroxylase, the key enzyme for the synthesis of 1alpha,25-dihydroxyvitamin D3.
We cloned human 25-hydroxyvitamin D3 1alpha-hydroxylase complementary DNA (cDNA) using a mouse 1alpha-hydroxylase cDNA fragment as a probe. Its genomic structure was determined, and its chromosomal location was mapped by fluorescence in situ hybridization. We then identified mutations in the 1alpha-hydroxylase gene in four unrelated patients with pseudovitamin D-deficiency rickets by DNA-sequence analysis. Both the normal and the mutant 1alpha-hydroxylase proteins were expressed in COS-1 cells and were assayed for 1alpha-hydroxylase activity.
The gene for 25-hydroxyvitamin D3 1alpha-hydroxylase was mapped to chromosome 12q13.3, which had previously been reported to be the locus for pseudovitamin D-deficiency rickets by linkage analysis. Four different homozygous missense mutations were detected in this gene in the four patients with pseudovitamin D-deficiency rickets. The unaffected parents and one sibling tested were heterozygous for the mutations. Functional analysis of the mutant 1alpha-hydroxylase protein revealed that all four mutations abolished 1alpha-hydroxylase activity.
Inactivating mutations in the 25-hydroxyvitamin D3 1alpha-hydroxylase gene are a cause of pseudovitamin D-deficiency rickets.
假性维生素D缺乏性佝偻病的特征是佝偻病早期发作并伴有低钙血症，被认为是由肾25-羟维生素D3 1α-羟化酶（合成1α,25-二羟维生素D3的关键酶）缺乏所致。
我们以小鼠1α-羟化酶cDNA片段为探针克隆人25-羟维生素D3 1α-羟化酶互补DNA（cDNA）。确定其基因组结构，并通过荧光原位杂交对其染色体定位进行图谱分析。然后，我们通过DNA序列分析在4例无亲缘关系的假性维生素D缺乏性佝偻病患者中鉴定1α-羟化酶基因的突变。正常和突变的1α-羟化酶蛋白均在COS-1细胞中表达，并检测其1α-羟化酶活性。
25-羟维生素D3 1α-羟化酶基因定位于12q13.3染色体，此前通过连锁分析已报道该位点为假性维生素D缺乏性佝偻病的位点。在4例假性维生素D缺乏性佝偻病患者的该基因中检测到4种不同的纯合错义突变。未受影响的父母和一名受测同胞为这些突变的杂合子。对突变的1α-羟化酶蛋白的功能分析显示，所有4种突变均消除了1α-羟化酶活性。
25-羟维生素D3 1α-羟化酶基因的失活突变是假性维生素D缺乏性佝偻病的病因。
