Miyajima H, Shimizu T, Kaneko E
First Department of Medicine, Hamamatsu University School of Medicine.
Rinsho Shinkeigaku. 1992 Oct;32(10):1087-92.
A 33-year-old female complained of muscle pain and stiffness after severe exercise from the age of nine. Her sister also had similar symptoms. Consanguinity was found in her parents. Neither muscle wasting nor weakness was detectable. The activity of LDH in the muscle was decreased less to than 8% of normal value. The isoenzyme pattern of the muscle LDH revealed only one band of B4. The levels of blood lactate did not rise on anaerobic exercise, while a marked increase of pyruvate was found. Northern blot analysis showed that the ratio of LDH-A transcript to beta-actin transcript in the patient was similar to that in a normal subject. RNA preparations were reverse-transcribed, amplified by a polymerase chain reaction (PCR), and separated by electrophoresis. The size of PCR product corresponding to exon 6 was decreased. The nucleotide sequence of this product was determined and a 20 bp deletion was found. This mutation results in a frame-shift translation and premature termination. The predicted incomplete LDH-A subunit contains only 259 instead of 331 amino acids. Immunofluorescence for LDH-A subunit could be seen within the cytoplasm and on the surface membrane of the muscle fibers in our patient as well as control subjects by the immunohistochemical studies. These findings suggest that LDH-A mRNA is transcribed in a truncated form and an enzymatically inactive protein is produced in the patient's muscles.
一名33岁女性自9岁起便抱怨剧烈运动后出现肌肉疼痛和僵硬。她的姐姐也有类似症状。其父母存在近亲关系。未检测到肌肉萎缩或无力。肌肉中乳酸脱氢酶（LDH）的活性降至正常水平的8%以下。肌肉LDH的同工酶谱仅显示一条B4带。无氧运动时血乳酸水平未升高，而丙酮酸显著升高。Northern印迹分析显示，患者中LDH - A转录本与β - 肌动蛋白转录本的比例与正常受试者相似。RNA制剂经逆转录、通过聚合酶链反应（PCR）扩增并进行电泳分离。对应于外显子6的PCR产物大小减小。测定了该产物的核苷酸序列，发现有20 bp的缺失。这种突变导致移码翻译和提前终止。预测的不完整LDH - A亚基仅包含259个而非331个氨基酸。通过免疫组织化学研究，在我们的患者以及对照受试者的肌纤维细胞质和表面膜内均可看到LDH - A亚基的免疫荧光。这些发现表明，患者肌肉中LDH - A mRNA以截短形式转录，并产生了无酶活性的蛋白质。
