Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a rare X-linked 
disorder caused by deficient activity of the lysosomal enzyme, 
iduronate-2-sulfatase (IDS). Phenotypic expression of MPS II in female patients 
rarely occurs and may be the result of (i) structural abnormalities of the X 
chromosome, (ii) homozygosity for disease-causing mutations, or (iii) skewed 
X-chromosome inactivation, in which the normal IDS allele is preferentially 
inactivated and the abnormal IDS allele is active. We report here on a female 
patient with clinical MPS II manifestations, deficiency of IDS enzyme activity 
and a de novo balanced reciprocal X;9 translocation. As our patient has a skewed 
XCI pattern, but neither genomic IDS mutations nor abnormal IDS transcripts were 
detected, we speculate about the possible role of the chromosomal rearrangement 
in reducing the IDS translation efficiency.