BackgroundMucopolysaccharidosis type VI (Maroteaux-Lamy syndrome; MPS VI) is an autosomal recessive lysosomal storage disorder in which deficiency of N-acetylgalactosamine 4-sulfatase (arylsulfatase B; ARSB) leads to the storage of glycosaminoglycans (GAGs) in connective tissue. The genotype-phenotype correlation has been addressed in several publications but the picture is not complete. Since 2007, enzyme-replacement therapy (ERT) has been available for patients with MPS VI in the Netherlands. The purpose of our study was to learn more about the genotype-phenotype correlations in MPS VI and the antibody response to ERT with galsulfase (recombinant human arylsulfatase B).MethodsWe identified ARSB mutations in 12 patients and used site-directed mutagenesis to study their effect. Antibody levels to galsulfase were measured using ELISA and a semi-quantitative immunoprecipitation method. We assessed the in vitro inhibitory effect of antibodies on galsulfase uptake and their effect on clinical outcome.ResultsFive patients had a rapidly progressive phenotype and seven a slowly progressive phenotype. In total 9 pathogenic mutations were identified including 4 novel mutations (N301K, V332G, A237D, and c.1142 + 2 T > C) together composing 8 pathogenic genotypes. Most mutations appeared not to affect the synthesis of ARSB (66 kD precursor), but to hamper its maturation (43 kD ARSB). Disease severity was correlated with urinary GAG excretion. All patients developed antibodies to galsulfase within 26 weeks of treatment. It was demonstrated that these antibodies can inhibit the uptake of galsulfase in vitro.ConclusionsThe clinical phenotypes and the observed defects in the biosynthesis of ARSB show that some of the mutations that we identified are clearly more severe than others. Patients receiving galsulfase as enzyme-replacement therapy can develop antibodies towards the therapeutic protein. Though most titers are modest, they can exceed a level at which they potentially affect the clinical outcome of enzyme-replacement therapy.

With or without intellectual disabilities, many MPS patients experience pain. We recommend that standardized pain assessments are included in the regular follow-up program of patients with MPS.

BackgroundIt remains unclear to what extent the brain is affected by Maroteaux-Lamy syndrome (MPS VI), a progressive lysosomal storage disorder. While enzyme replacement therapy (ERT) elicits positive effects, the drug cannot cross the blood–brain barrier. We therefore studied cognitive development and brain abnormalities in the Dutch MPS VI patient population treated with ERT.MethodsIn a series of 11 children with MPS VI (age 2 to 20 years), we assessed cognitive functioning and brain magnetic resonance imaging prospectively at the start of ERT and at regular times thereafter up to 4.8 years. We also assessed the children’s clinical characteristics, their siblings’ cognitive development, and their parents’ educational levels.ResultsThe patients’ intelligence scores ranged from normal to mentally delayed (range test scores 52–131). In 90 %, their scores remained fairly stable during follow-up, generally lying in the same range as their siblings’ test scores (median for patients = 104, median for siblings = 88) and comparing well with the parental educational levels. Native-speaking patients had higher intelligence test scores than non-native-speaking patients. Two patients, both with high baseline glycosaminoglycan levels in their urine and severe mutations in the arylsulfatase B gene, scored clearly lower than expected. Patients with pY210C performed best. Brain abnormalities were aspecific, occurring more in patients with severe symptoms.ConclusionOur study shows that cognitive development in MPS VI patients is determined not only by familial and social-background factors, but, in patients with a severe form of the disease, also by the disease itself. Therefore in patients with severe disease presentation cognition should be monitored carefully.Electronic supplementary materialThe online version of this article (doi:10.1007/s10545-015-9895-8) contains supplementary material, which is available to authorized users.

Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI) is a rare lysosomal storage disorder in which the pathologic storage of glycosaminoglycans in various tissues can lead to severe symptoms, including cardiomyopathy. We report on a child with Maroteaux-Lamy syndrome whose cardiac condition deteriorated and eventually led to cardiac failure at the age of 7 years due to severe mitral regurgitation. She received a mitral valve replacement and tricuspid repair with successful outcome. Histologic examination of the mitral valve showed abundant "clear" cells in both the leaflets and chordae tendineae. In Hurler disease (MPS I), similar cells have been identified as activated valvular interstitial cells (VICs, a myofibroblast like cell type). Here we report that the "clear" cells are CD68 positive, a frequently used marker of macrophage lineage. The "clear" cells remained unstained with the more specific macrophage marker CD14 while persistent staining of other cells demonstrated macrophage infiltration. From these observations, we infer that macrophages are involved in mitral valve pathology in MPS VI.

NANS‐CDG is a congenital disorder of glycosylation (CDG) caused by biallelic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. It presents with intellectual developmental disorder (IDD), skeletal dysplasia, neurologic impairment, and gastrointestinal dysfunction. Some patients suffer progressive intellectual neurologic deterioration (PIND), emphasizing the need for a therapy. In a previous study, sialic acid supplementation in knockout nansa zebrafish partially rescued skeletal abnormalities. Here, we performed the first in‐human pre‐ and postnatal sialic‐acid study in NANS‐CDG. In this open‐label observational study, 5 patients with NANS‐CDG (range 0–28 years) were treated with oral sialic acid for 15 months. The primary outcome was safety. Secondary outcomes were psychomotor/cognitive testing, height and weight, seizure control, bone health, gastrointestinal symptoms, and biochemical and hematological parameters. Sialic acid was well tolerated. In postnatally treated patients, there was no significant improvement. For the prenatally treated patient, psychomotor and neurologic development was better than two other genotypically identical patients (one treated postnatally, one untreated). The effect of sialic acid treatment may depend on the timing, with prenatal treatment potentially benefiting neurodevelopmental outcomes. Evidence is limited, however, and longer‐term follow‐up in a larger number of prenatally treated patients is required.