Department of Medical Genetics, Genome-Scale Biology Research Program, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland.
Gastroenterology. 2012 Dec;143(6):1482-1491.e3. doi: 10.1053/j.gastro.2012.08.045. Epub 2012 Sep 6.
BACKGROUND & AIMS: Familial visceral myopathy (FVM) is a rare inherited form of myopathic pseudo-obstruction; little is known about the genetic factors that cause this disorder. FVM is characterized by impaired functions of enteric smooth muscle cells, resulting in abnormal intestinal motility, severe abdominal pain, malnutrition, and even death. We searched for genetic factors that might cause this disorder.
We performed whole-exome sequence analysis of blood samples from 2 individuals in a family that had 7 members diagnosed with FVM. Sanger sequencing was used to analyze additional family members and 280 individuals without this disorder (controls). Intestinal tissue samples from 4 patients and 2 controls were analyzed by immunohistochemistry. Functional studies, including immunofluorescence, cell contractility, and actomyosin structure analyses, were performed using CRL-1976 and U2OS sarcoma cell lines.
Whole-exome sequence analysis of DNA from 2 siblings identified 83 gene variants that were shared between the siblings and considered as possible disease-causing changes. A heterozygous variant, R148S in enteric smooth muscle actin γ-2 (ACTG2), segregated with disease phenotype. Intestinal smooth muscle (muscularis propria) from individuals with FVM had reduced levels of cytoplasmic ACTG2 and abnormal accumulation of the protein into intracellular inclusions compared with controls. Sarcoma cells that expressed exogenous ACTG2(R148S) incorporated reduced amounts of this protein into actin filaments compared with cells expressing ACTG2(wt) (P < .001). ACTG2(R148S) also interfered with actin cytoskeleton organization and the contractile activities of the cells, indicating a dominant-negative effect. These findings, along with the site of the variation in the protein, indicate that ACTG2 R148S interferes with actin filament assembly.
We identified the R148S variant in ACTG2 as a cause of FVM in one family. The altered ACTG2 protein appears to aggregate, rather than form actin filaments, in intestinal smooth muscle tissue. This defect could impair contraction of the visceral smooth muscle cells and reduce bowel motility.
家族性内脏肌病（FVM）是一种罕见的遗传性肌病性假性肠梗阻形式；导致这种疾病的遗传因素知之甚少。FVM 的特征是肠平滑肌细胞功能受损，导致肠道运动异常、严重腹痛、营养不良，甚至死亡。我们寻找可能导致这种疾病的遗传因素。
我们对一个家族的 2 名成员的血液样本进行了全外显子组测序，该家族有 7 名成员被诊断为 FVM。对其他家族成员和 280 名无此疾病的个体（对照）进行 Sanger 测序分析。对 4 名患者和 2 名对照的肠道组织样本进行免疫组织化学分析。使用 CRL-1976 和 U2OS 肉瘤细胞系进行免疫荧光、细胞收缩性和肌动球蛋白结构分析等功能研究。
对 2 名兄弟姐妹的 DNA 进行全外显子组测序发现，83 个基因变异在兄弟姐妹之间共享，并被认为是可能导致疾病的变化。一种杂合变体，即肌球蛋白轻链 2 （ACTG2）中的 R148S，与疾病表型分离。与对照组相比，FVM 个体的肠道平滑肌（固有层）中的细胞质 ACTG2 水平降低，并且该蛋白异常积累到细胞内包涵体中。与表达野生型 ACTG2（wt）的细胞相比，表达外源性 ACTG2（R148S）的肉瘤细胞将这种蛋白掺入肌动蛋白丝的量减少（P<0.001）。ACTG2（R148S）还干扰了细胞的肌动蛋白细胞骨架组织和收缩活性，表明具有显性负效应。这些发现以及该蛋白变异的位置表明，ACTG2 R148S 干扰了肌动蛋白丝的组装。
我们在一个家族中鉴定出 ACTG2 的 R148S 变体是 FVM 的原因。改变的 ACTG2 蛋白似乎在肠道平滑肌组织中聚集，而不是形成肌动蛋白丝。这种缺陷可能会损害内脏平滑肌细胞的收缩并降低肠道蠕动。
