FAMILIAL GLUCOSE GALACTOSE MALABSORPTION

葡萄糖-半乳糖吸收不良(GGM)的特征是 新生儿出现几次腹泻，导致死亡，除非 有害的糖类会从饮食中去除。它是由一种 刷状缘钠/葡萄糖共转运蛋白(SGLT1)缺陷。我们 已经确定了转运蛋白，克隆并绘制了基因图，以及 在33名患者中发现了导致这种疾病的突变。 现在的目标是了解人的分子和细胞生物学 GGM。我们计划：继续筛查新患者的突变； 确定突变是如何导致吸收不良的；设计新的 治疗病人的疗法；并解决是否携带 GGM突变会损害葡萄糖的吸收。新病人 将使用基因组DNA，外显子的聚合酶链式反应扩增， 单链构象多态性(SSCP)凝胶，以及 测序。90%的突变发生在基因编码中 区域和结果产生突变和截断 蛋白质。我们的假设是截短的蛋白质是 且突变蛋白不会插入到血浆中 薄膜。我们将通过表达突变体来检验这一假设 非洲爪哇卵母细胞利用电生理学， 免疫学、生化和显微技术。一旦 糖类转运受损的原因在模型中确定 表达系统，我们将在活检样本中进行测试 病人。在那些突变导致基因缺陷的情况下 SGLT1蛋白在内质网和 质膜，我们将制定策略来增加 将SGLT1输送到质膜。最后，在家庭中 在我们发现GGM突变的地方，我们将对家族进行筛查 杂合子和正常纯合子的成员。糖 将使用H呼气测试来测量吸收，以确定是否 携带者表现出任何吸收不良的症状。这项研究将 使我们能够识别和治疗糖吸收不良的患者 由于SGLT1基因的突变，将提供独特的 关于合成、贩运和职能的信息 辅助传送器。

Glucose-Galactose Malabsorption (GGM) is characterized by a neonatal onset of a several diarrhea that results in death unless the offending sugars are removed from the diet. It is caused by a defect in the brush border Na/glucose cotransporter (SGLT1). We have identified the transporter, cloned and mapped the gene, and found the mutations responsible for the disease in 33 patients. The goal now is to understand the molecular and cell biology of GGM. We plan to: continue screening new patients for mutations; determine how the mutations cause the malabsorption; devise new therapies to treat patients; and resolve whether or not carriers of GGM mutations have impaired glucose absorption. New patients will be screened using genomic DNA, PCR-amplification of exons, single strand conformational polymorphism (SSCP) gels, and sequencing. 90 percent of the mutations are in the gene coding region and result in the production of mutant and truncated proteins. Our hypothesis is that the truncated proteins are defective and that mutant proteins are not inserted into the plasma membrane. We will test this hypothesis by expressing mutants in Xenopus laevis oocytes an using electrophysiological, immunological, biochemical and microscopic techniques. Once the reason for impaired sugar transport is determined in the model expression system, we will test this in biopsy samples from the patients. In those cases where mutations cause a defect in trafficking SGLT1 protein between the endoplasmic reticulum and the plasma membrane, we will devise strategies to increase the delivery of SGLT1 to the plasma membrane. Finally, in kindreds where we have identified GGM mutations, we will screen family members for heterozygotes and normal homozygotes. Sugar absorption will be measured using H-breath tests to determine if carriers exhibit any symptoms of malabsorption. This study will enable us to identify and treat patients with sugar malabsorption due to mutations in the SGLT1 gene, and will provide unique information about the synthesis, trafficking and function of the cotransporter.