黑白花奶牛“白细胞粘附缺陷症”（LAD）的分子生物学分析与诊断

从一患白细胞粘附缺陷症（ＬＡＤ）的黑白花奶牛犊的核苷酸顺序分析中，发现牛的抗原分子分化群１８（ＣＤ１８）的基因密码有二处发生了点突变；一处在第３８３核苷酸上，在此处原有的腺瞟吟已被鸟嘌呤取代；另一处在第７７５核苷酸上，在此处原有的胞嘧啶被胸腺嘧啶取代了。在第７７５核苷酸的突变是静止的，因为它并没有使其相应的氨基酸顺序发生改变。在第３８３核苷酸的突变，使其在相应的氨基酸顺序中第１２８位氨基酸位置上的天门冬氨酸被甘氨酸（Ｄ１２８Ｇ）所替代。一种用于牛的Ｄ１２８Ｇ等位基因的快速筛选诊断方法已作了说明。在美国，在黑白花奶牛中Ｄ１２８Ｇ等位基因的携带率在公牛中占１４．１％，在母牛中占５．８％。这一突变基因已流行于世界各地的黑白花奶牛之中。

The Molecular and Biological Identification of "Ieukocyte Adhesion Deficiency" (LAD) in Holstein Cattle

In the .analysis of the sequence from a Holstein calf afflicted with leukocyte adhesion deficiency (LAD), two point mutations were detected within the gene encoding bovine CD18: one mutation replaced adenine at the nucleotide 383 with guanine, and the other mutation replaced the cytosine at the nucleotide 775 with thymine. The mutation at the nucleotide 775 was silent, because it did not alter the deduced amino acid sequence. The mutation at the nucleotide 383 caused an aspartic acid to glycine substitution at the amino acid 128 (D128G). A method was described to rapidly screen cattle for the (D128G) allele. The carrier frequency for the (D128G) allele among Holstein cattle in the United States is 14. 1% among bulls and 5. 8% among cows. This mutation is prevalent among Holstein cattle throughout the world.