Ianzano Leonarda, Young Edwin J, Zhao Xiao C, Chan Elayne M, Rodriguez M T, Torrado Maria V, Scherer Stephen W, Minassian Berge A
Department of Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada.
Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Canada.
Hum Mutat. 2004 Feb;23(2):170-176. doi: 10.1002/humu.10306.
Lafora disease is the most severe teenage-onset progressive epilepsy, a unique form of glycogenosis with perikaryal accumulation of an abnormal form of glycogen, and a neurodegenerative disorder exhibiting an unusual generalized organellar disintegration. The disease is caused by mutations of the EPM2A gene, which encodes two isoforms of the laforin protein tyrosine phosphatase, having alternate carboxyl termini, one localized in the cytoplasm (endoplasmic reticulum) and the other in the nucleus. To date, all documented disease mutations, including the knockout mouse model deletion, have been in the segment of the protein common to both isoforms. It is therefore not known whether dysfunction of the cytoplasmic, nuclear, or both isoforms leads to the disease. In the present work, we identify six novel mutations, one of which, c.950insT (Q319fs), is the first mutation specific to the cytoplasmic laforin isoform, implicating this isoform in disease pathogenesis. To confirm this mutation's deleterious effect on laforin, we studied the resultant protein's subcellular localization and function and show a drastic reduction in its phosphatase activity, despite maintenance of its location at the endoplasmic reticulum.
拉福拉病是最严重的青少年期起病的进行性癫痫，是糖原贮积病的一种独特形式，其特征为糖原异常形式在核周积聚，也是一种神经退行性疾病，表现出异常的全身性细胞器解体。该疾病由EPM2A基因突变引起，该基因编码两种不同羧基末端的拉福林蛋白酪氨酸磷酸酶同工型，一种定位于细胞质（内质网），另一种定位于细胞核。迄今为止，所有已记录的疾病突变，包括基因敲除小鼠模型中的缺失，都发生在两种同工型共有的蛋白质片段中。因此，尚不清楚细胞质同工型、核同工型或两者的功能障碍是否会导致该疾病。在本研究中，我们鉴定出六个新突变，其中一个c.950insT（Q319fs）是第一个特定于细胞质拉福林同工型的突变，提示该同工型与疾病发病机制有关。为了证实该突变对拉福林的有害作用，我们研究了所得蛋白质的亚细胞定位和功能，结果显示尽管其在内质网中的位置得以维持，但其磷酸酶活性却大幅降低。
