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Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) activity. Diagnosis can be challenging and requires agreement of clinical, radiographic, and laboratory findings. A group of biochemical genetics laboratory directors and clinicians involved in the diagnosis of MPS IVA, convened by BioMarin Pharmaceutical Inc., met to develop recommendations for diagnosis. The following conclusions were reached. Due to the wide variation and subtleties of radiographic findings, imaging of multiple body regions is recommended. Urinary glycosaminoglycan analysis is particularly problematic for MPS IVA and it is strongly recommended to proceed to enzyme activity testing even if urine appears normal when there is clinical suspicion of MPS IVA. Enzyme activity testing of GALNS is essential in diagnosing MPS IVA. Additional analyses to confirm sample integrity and rule out MPS IVB, multiple sulfatase deficiency, and mucolipidoses types II/III are critical as part of enzyme activity testing. Leukocytes or cultured dermal fibroblasts are strongly recommended for enzyme activity testing to confirm screening results. Molecular testing may also be used to confirm the diagnosis in many patients. However, two known or probable causative mutations may not be identified in all cases of MPS IVA. A diagnostic testing algorithm is presented which attempts to streamline this complex testing process.

We analyzed placental tissue in one fetus with MPS II (iduronate sulphatase deficiency) and another with MPS VI (arylsulfatase B deficiency). Both were diagnosed prenatally, but families decided to continue pregnancies and placentas were collected at birth. We were able to demonstrate early storage of GAGs in both diseases by GAG measurement and microscopy analysis. Our results suggest that some alterations related to MPS storage, although not pronounced, may be observed in placental tissue of patients affected by MPS II and MPS VI., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Mucopolysacchariodosis type VI (MPS VI) is the lysosomal storage disorder caused by the deficient activity of arylsulfatase B (ASB; N-acetylgalactosamine 4-sulfatase) and the subsequent accumulation of the glycosaminoglycan (GAG), dermatan sulfate. In this study, a retroviral vector containing the full-length human ASB cDNA was constructed and used to transduce skin fibroblasts, chondrocytes, and bone marrow cells from human patients, cats, or rats with MPS VI. The ASB vector expressed high levels of enzymatic activity in each of the cell types tested and, in the case of cat and rat cells, enzymatic expression led to complete normalization of 35SO4 incorporation. In contrast, overexpression of ASB in human MPS VI skin fibroblasts did not lead to metabolic correction. High-level ASB expression was detected for up to eight weeks in transduced MPS VI cat and rat bone marrow cultures, and PCR analysis demonstrated retroviral-mediated gene transfer to approximately 30-50% of the CFU GM-derived colonies. Notably, overexpression of ASB in bone marrow cells led to release of the enzyme into the media and uptake by MPS VI cat and rat skin fibroblasts and/or chondrocytes via the mannose-6-phosphate receptor system, leading to metabolic correction. Thus, these studies provide important rationale for the development of gene therapy for this disorder and lay the frame-work for future in vivo studies in the animal model systems.

Two children of second-cousin parents were found to have a very mild form of Morquio syndrome. The 14-year-old boy was 147 cm tall and had fine corneal deposits, a broad chest, dislocated hips, and flat feet. His 7-year-old sister had a broad chest but otherwise normal physical development. An abnormal lumbar spine was seen in radiographs of both children. Analysis of the urine from the affected children showed levels of acid mucopolysaccharides (AMPS) up to twice as high as that found in normal urine, but no evidence of keratosulfaturia. Most urinary AMPS was chondroitin-6-sulfate. Multiple assays of N-acetylgalactosamine-6-sulfate (GalNAc-6-SO4) sulfatase in leukocytes and cultured skin fibroblasts showed deficiency of this enzyme in the range found in the classical form of Morquio (Morquio A) syndrome. This report identifies an enzymatic defect in one form of non-keratan-sulfate-excreting Morquio (NKSE Morquio) syndrome and confirms the absence of keratosulfaturia in this mild form of Morquio disease.

Upon incubation of keratan [35S]sulphate with normal fibroblasts both [35S]sulphate and N-acetylglucosamine 6-[35S]sulphate are liberated. From the products obtained after digestion with various mutant fibroblasts and with purified N-acetylgalactosamine 6-sulphate sulphatase we suggest that (i) [35S]sulphate is released almost exclusively from galactose 6-sulphate residues; (ii) N-acetylgalactosamine 6-sulphate sulphatase exhibits galactose 6-sulphate sulphatase activity; (iii) both sulphatase activities are deficient in Morquio disease type A.