p.X654R IDUA variant among Thai individuals with intermediate mucopolysaccharidosis type I and its residual activity as demonstrated in COS‐7 cells

• Published in: Annals of human genetics Vol. 82; no. 3; pp. 150 - 157
• Main Authors: Ngiwsara, Lukana, Ketudat‐Cairns, James R., Sawangareetrakul, Phannee, Charoenwattanasatien, Ratana, Champattanachai, Voraratt, Kuptanon, Chulaluck, Pangkanon, Suthipong, Tim‐Aroon, Thipwimol, Wattanasirichaigoon, Duangrurdee, Svasti, Jisnuson
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.05.2018
• Subjects: Alleles; Alpha‐L‐iduronidase; Amino acid sequence; Enzymatic activity; Enzymes; Genetic analysis; Hereditary diseases; Heterozygosity; Hurler‐Scheie syndrome; IDUA gene; IDUA mutation; Leukocytes; Mucopolysaccharidosis; Mucopolysacharidosis; Mutation; Proteins; Mucopolysacharidosis; IDUA mutation; Alpha-L-iduronidase; Hurler-Scheie syndrome
• ISSN: 0003-4800; 1469-1809
• DOI: 10.1111/ahg.12236

Background 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. Methods 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. Results 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. Conclusions 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.