Metabolism & Genetics Group, Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL), Faculty of Pharmacy, University of Lisbon, Av. Prof. Gama Pinto, 1643-009, Lisbon, Portugal.
J Inherit Metab Dis. 2014 Jan;37(1):43-52. doi: 10.1007/s10545-013-9623-1. Epub 2013 Jun 8.
Classic galactosemia is an autosomal recessive disorder caused by deficient galactose-1-phosphate uridylyltransferase (GALT) activity. Patients develop symptoms in the neonatal period, which can be ameliorated by dietary restriction of galactose. Many patients develop long-term complications, with a broad range of clinical symptoms whose pathophysiology is poorly understood. The high allelic heterogeneity of GALT gene that characterizes this disorder is thought to play a determinant role in biochemical and clinical phenotypes. We aimed to characterize the mutational spectrum of GALT deficiency in Portugal and to assess potential genotype-phenotype correlations. Direct sequencing of the GALT gene and in silico analyses were employed to evaluate the impact of uncharacterized mutations upon GALT functionality. Molecular characterization of 42 galactosemic Portuguese patients revealed a mutational spectrum comprising 14 nucleotide substitutions: ten missense, two nonsense and two putative splicing mutations. Sixteen different genotypic combinations were detected, half of the patients being p.Q188R homozygotes. Notably, the second most frequent variation is a splicing mutation. In silico predictions complemented by a close-up on the mutations in the protein structure suggest that uncharacterized missense mutations have cumulative point effects on protein stability, oligomeric state, or substrate binding. One splicing mutation is predicted to cause an alternative splicing event. This study reinforces the difficulty in establishing a genotype-phenotype correlation in classic galactosemia, a monogenic disease whose complex pathogenesis and clinical features emphasize the need to expand the knowledge on this "cloudy" disorder.
经典型半乳糖血症是一种常染色体隐性遗传病，由半乳糖-1-磷酸尿苷酰转移酶（GALT）活性缺陷引起。患者在新生儿期出现症状，通过限制饮食中的半乳糖可改善症状。许多患者会出现长期并发症，具有广泛的临床症状，其病理生理学尚未完全了解。这种疾病的 GALT 基因突变具有高度的等位基因异质性，被认为在生化和临床表型中起决定作用。我们旨在描述葡萄牙 GALT 缺乏症的突变谱，并评估潜在的基因型-表型相关性。通过直接测序 GALT 基因和计算机分析来评估未明突变对 GALT 功能的影响。对 42 名葡葡牙半乳糖血症患者的分子特征进行了分析，结果发现突变谱包括 14 个核苷酸取代：10 个错义突变、2 个无义突变和 2 个可能的剪接突变。共检测到 16 种不同的基因型组合，其中一半患者为 p.Q188R 纯合子。值得注意的是，第二常见的变异是剪接突变。计算机预测结合对蛋白质结构中突变的详细分析表明，未明义突变对蛋白质稳定性、寡聚状态或底物结合具有累积的点效应。一个剪接突变预计会导致另一个剪接事件。本研究进一步证实了在经典型半乳糖血症中建立基因型-表型相关性的困难，这种单基因疾病的复杂发病机制和临床特征强调了需要扩展对这种“模糊”疾病的认识。
