Mucopolysaccharidosis type VI on enzyme replacement therapy since infancy: Six years follow-up of four children

Clinical and biochemical improvements are reported on Mucopolysaccharidosis type VI (MPS VI) patients on Enzyme Replacement Therapy (ERT) with rhASB (galsulfase, Naglazyme®), and preclinical and clinical studies have shown clinical benefits of early initiation. We report four unrelated MPS VI children who began ERT as infants (ages 5 days–10 months). The three older patients showed the first clinical signs of MPS VI at baseline, also presenting different degrees of dysostosis multiplex, and two had mild heart disease. The two oldest also had mild facial coarseness, one had hearing conduction deficit and sleep disorder and the other corneal clouding at baseline. After six years on ERT, all four patients have normal urinary GAG values. Although they all showed normal motor and mental development, brain and cervical spine MRI images available from two of the older patients showed abnormalities, while the youngest child continues having normal images. The four patients presented slower progression of bone and joint disease when compared to their affected older siblings. It should be noticed that only two patients in this sample are currently below the 3rd percentile for height: the youngest who has a constitutional factor associated and the eldest who already presented frank dysostosis at 10 months of age. These findings confirm previous studies that report that skeletal features of the disease cannot be completely prevented despite early ERT. Heart disease already present in two of the four infants at baseline got worse over time and appeared in another patient, but the youngest child on ERT introduction still has a normal echocardiogram at six years of age; he also is the only one without corneal clouding after six years follow-up. Our results also suggest that early ERT prevented storage in spleen and liver and may also have improved or prevented progression of facial dysmorphic features, corroborating similar findings seen in previous studies. No safety concerns were identified and none of the patients experienced a serious adverse event. The baseline severity of the disorder of these four infants seems related to age and it is tempting to say that severity on the first year of life is progressive and ERT effectiveness is indirectly related to it. Despite being known that MPS VI progresses differently among patients, the fact that these infants had a slower progression than their older siblings speaks in favor of a very early start of ERT. In conclusion, this report confirms the early manifestations of the disease and provides additional evidence on safety and of the beneficial effects of ERT in patients less than 1 year of age.