Mucopolysaccharidosis type I (MPS IS) is a rare autosomal recessive disease caused by a deficiency of the lysosomal enzyme alpha-L-iduronidase, which is involved in the degradation of sulfated glycosaminoglycans (GAGs). The deficiency results in the intra-and pericellular accumulation of the GAGs heparan sulfate and dermatan sulfate. Eight adult patients with typical features of MPS IS aged 31.5 +/- 6.8 years (five men) were included and compared to age-and gender-matched controls. With transthoracic echocardiography, cyclic ascending aortic diameter changes were measured and ascending aortic elastic properties were calculated to characterize aortic elasticity. In MPS IS patients, aortic stiffness index was significantly increased (23.1 +/- 10.4 vs 3.9 +/- 1.5, P < 0.001), while aortic distensibility was significantly decreased (1.6 +/- 0.8 vs 4.6 [corrected] +/- 1.9 cm(2)/dynes [corrected] 10(-6), P < 0.001) compared to age-and sex-matched controls. The results of the present study demonstrate that in addition to the known cardiac complications, MPS IS patients have an impairment of ascending aortic elasticity. Further follow-up studies are needed to examine arterial elasticity using other methods in this patient population, and to detect possible effects of enzyme replacement therapy.