Ngiwsara Lukana, Ketudat-Cairns James R, Sawangareetrakul Phannee, Charoenwattanasatien Ratana, Champattanachai Voraratt, Kuptanon Chulaluck, Pangkanon Suthipong, Tim-Aroon Thipwimol, Wattanasirichaigoon Duangrurdee, Svasti Jisnuson
Laboratory of Biochemistry, Chulabhorn Research Institute, Bangkok, Thailand.
School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
Ann Hum Genet. 2018 May;82(3):150-157. doi: 10.1111/ahg.12236. Epub 2017 Dec 28.
Mucopolysaccharidosis type I (MPS I) is a rare autosomal-recessive disorder caused by defects in alpha-L-iduronidase (IDUA), a lysosomal enzyme encoded by the IDUA gene. Herein, we characterized IDUA mutations underlying mucopolysaccharidosis type I intermediate form (Hurler-Scheie syndrome) and its molecular pathogenic mechanisms.
Clinical data, activity of the IDUA enzyme in leukocytes, and a mutation of the IDUA gene were analyzed. Pathogenesis associated with an IDUA mutation was further investigated by evaluating the mutant cDNA sequence, protein expression and activity in COS-7 cells.
Five unrelated patients were identified to have clinical diagnosis of intermediate form of MPS I (Hurler-Scheie) and exhibited low-to-absent levels of leukocyte IDUA activity. Genetic analysis revealed homozygous c.*1T>C (p.X654R) mutation in two patients and compound heterozygosity between the c.*1T>C and another allele including c.265G>A (p.R89Q), c.935G>A (p.W312X), or c.1138 C>T (p.Q380X), each in a single patient. Sequencing the 3'RACE product of the c.*1T>C (p.X654R) allele indicated a 38-amino acids elongation of the mutant protein. COS-7 cells expressing IDUA with the mutations exhibited extremely low levels or complete absence of enzyme activity compared to wild-type IDUA. Western blot analysis detected no protein in p.W312X and p.Q380X samples, while an elevated molecular mass and a different pattern of protein bands were found in p.X654R specimen compared with the wild type IDUA.
Mutational spectrum underlying intermediate MPS I is expanded. Our data suggest that the p.X654R is an intermediate IDUA mutant allele with residual enzyme activity. It can lead to intermediate or milder form of MPS I depending on another associated allele.
I型黏多糖贮积症（MPS I）是一种罕见的常染色体隐性疾病，由α-L-艾杜糖醛酸酶（IDUA）缺陷引起，IDUA是一种由IDUA基因编码的溶酶体酶。在此，我们对I型黏多糖贮积症中间型（Hurler-Scheie综合征）潜在的IDUA突变及其分子致病机制进行了表征。
分析临床数据、白细胞中IDUA酶的活性以及IDUA基因的突变。通过评估突变cDNA序列、蛋白质表达及在COS-7细胞中的活性，进一步研究与IDUA突变相关的发病机制。
鉴定出5例无亲缘关系的患者临床诊断为I型黏多糖贮积症中间型（Hurler-Scheie），白细胞IDUA活性水平低或缺失。基因分析显示，2例患者存在纯合子c.*1T>C（p.X654R）突变，另3例患者分别为c.*1T>C与另一个等位基因（包括c.265G>A（p.R89Q）、c.935G>A（p.W312X）或c.1138C>T（p.Q380X））的复合杂合子。对c.*1T>C（p.X654R）等位基因的3'RACE产物进行测序，结果表明突变蛋白延长了38个氨基酸。与野生型IDUA相比，表达带有这些突变的IDUA的COS-7细胞表现出极低水平或完全没有酶活性。蛋白质印迹分析在p.W312X和p.Q380X样本中未检测到蛋白质，而与野生型IDUA相比，p.X654R样本中发现分子量升高且蛋白带模式不同。
I型黏多糖贮积症中间型的突变谱得到了扩展。我们的数据表明，p.X654R是一个具有残余酶活性的IDUA中间突变等位基因。根据另一个相关等位基因的情况，它可导致I型黏多糖贮积症的中间型或较轻形式。
