Introduction

Unconjugated hyperbilirubinemia (UCB) is a feature of Gilbert's syndrome (GS) and Crigler-Najjar's syndrome (CNS), which are two hereditary defects in bilirubin metabolism. Both syndromes are linked to mutations in the UGT1A1 gene, which cause either the decrease or the absence of the UGT1A1 enzymatic activity. Here, we investigated the molecular basis of the UGT1A1 gene in Tunisian patients presenting with unconjugated hyperbilirubinemia.

Methods

Twenty-four patients with UCB were investigated. The screening protocol for hemoglobinopathies, enzymopathies, and membrane defects was executed in all patients. Afterward, the molecular analysis of the entire UGT1A1 gene was performed by DNA Sanger sequencing. Several bioinformatic tools were used to explore the effects of novel mutations.

Results

Fifteen different UGT1A1 variations were identified, among which four are described here for the first time. In exon 5, the c.1412C > G; p.(Ala471Gly) and c.1589C > T; p.(Ser530Phe) mutations were detected in patients presenting with CNS type I and GS, respectively. In the 3′UTR region of UGT1A1, the c.*90C > T mutation was detected in 3 patients with CNS type I. In the same region, the c.*388C > T defect was found in a GS patient. A deleterious and damaging effect on the UGT1A1 protein were predicted for both exonic mutations. Furthermore, novel microRNAs were identified as targetting the mutated sequences for the 3′UTR mutations.

Conclusion

Our study provides novel data on UCB among Tunisians. Furthermore, we report four novel mutations associated with both GS and CNS. The identification of these mutations increases the spectrum of the UGT1A1 mutations and contributes to an understanding of the molecular abnormalities associated with unconjugated hyperbilirubinemia.

中文翻译：

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非结合性高胆红素血症的突尼斯患者中铀酰二磷酸-葡萄糖醛酸转移酶1A1（UGT1A1）基因的新突变

介绍

未结合的高胆红素血症（UCB）是吉尔伯特综合征（GS）和克利格勒-纳杰尔综合征（CNS）的特征，这是胆红素代谢的两个遗传缺陷。这两个综合症都与UGT1A1基因的突变相关，这会导致UGT1A1酶活性的降低或缺失。在这里，我们调查了突尼斯患者中未结合高胆红素血症的UGT1A1基因的分子基础。

方法

研究了二十四例UCB患者。对所有患者均进行了血红蛋白病，酶病和膜缺损的筛查方案。然后，通过DNA Sanger测序对整个UGT1A1基因进行分子分析。几种生物信息学工具被用来探索新突变的影响。

结果

确定了15种不同的UGT1A1变体，其中有4种是首次在此进行描述。在外显子5中，c.1412C> G；p。（Ala471Gly）和c.1589C> T; 在患有CNS I型和GS的患者中分别检测到p。（Ser530Phe）突变。在UGT1A1的3'UTR区域中，在3例I型中枢神经系统患者中检测到c。* 90C> T突变。在同一区域中，在GS患者中发现了c。* 388C> T缺陷。预测两个外显子突变对UGT1A1蛋白的有害和破坏作用。此外，新的microRNA被确定为靶向3'UTR突变的突变序列。

结论

我们的研究为突尼斯人提供了有关UCB的新颖数据。此外，我们报告了与GS和CNS相关的四个新颖的​​突变。这些突变的鉴定增加了UGT1A1突变的范围，并有助于理解与未结合的高胆红素血症有关的分子异常。