Identification and characterization of ‐3c–g acceptor splice site mutation in human α‐ l‐iduronidase associated with mucopolysaccharidosis type IH/S

DNA screening for mutations in the α‐ l‐iduronidase (IDUA) gene was performed in a Chinese mucopolysaccharidosis type IH/S patient. The patient had two different mutations: the maternal allele has L346R (t–g transversion in codon 346) and the paternal allele has 388‐3c–g (c–g transversion at position ‐3 of the 3′ splice site of intron 2). In transfected COS‐7 cells, L346R showed no appreciable IDUA activity (0.4% of normal activity), although it did not cause an apparent reduction in IDUA mRNA or protein level. The 388‐3c–g mutation profoundly affects normal splicing leading to a very unstable mRNA. Expression of the IDUA cDNA containing the mutated acceptor splice site showed trace amounts of enzyme activity (1.6% of normal activity). The results provide further support for the importance of cytosine at the ‐3 position in RNA processing.