Role of novel and rare nucleotide substitutions of the β-globin gene

Abstract

The Laboratory for Molecular Prenatal Diagnosis of Hemoglobinopathies at the Villa Sofia-Cervello Hospital in Palermo, Italy, carries out an intensive screening program aimed at identifying the healthy carriers of thalassemia and, consequently, the couples at risk of bearing an affected fetus. The diagnostic process is basically divided into two phases: i) hematologic and hemoglobin data; ii) molecular analysis of globin genes and, when possible, a genetic study of the family. Since 2003, we have been performing DNA sequence analysis on those cases in which classical molecular methods failed to give a complete diagnostic response, particularly in phenotypes with borderline values of HbA2 with mild or absent microcytosis. During ten years of screening activities (from 2003 to 2012), twenty- seven unknown or rare nucleotide changes of the β-globin gene have been identified; hematologic and hemoglobin data have been carefully evaluated and, wherever possible, we have conducted a family study to evaluate whether a phenotypic expression could be associated to these nucleotide changes. Because of the limited numbers of cases for each mutation, the significance of these nucleotide substitutions has still not been fully clarified, and this raises a number of questions that need to be answered when carrying out appropriate genetic counseling for couples presumed to be at risk. 意大利巴勒莫Villa Sofia-Cervello医院血红蛋白病分子产前诊断实验室进行密集的筛选程序，旨在识别健康的地中海贫血携带者和有怀上地中海贫血胎儿风险的夫妇。 诊断过程基本上分为两个阶段：1）血液及血红蛋白数据；2）珠蛋白基因分子分析以及家族遗传研究（如有可能）。 自2003年以来，我们已对这类病例进行DNA序列分析：传统的分子方法无法给出完整的诊断响应，尤其是有轻微小红细胞症或缺乏小红细胞症的HbA2临界值表型。 通过十年筛选活动（2003年至2012年），已识别出β珠蛋白基因的27个未知或罕见的核苷酸变化；仔细评估过血液和血红蛋白数据，在可能的情况下，我们已进行家系研究，以确定表型表达是否与这些核苷酸变化相关。由于只有有限的突变案例，所以至今尚未完全证实这些核苷酸置换的重要性，并对假定存在患病风险的夫妇开展适当的基因遗传咨询时，因此引起了大量需要解答的问题。

Keywords

• thalassemia, nucleotide substitutions, genetic counseling.