Optimizing the Molecular Diagnosis of GALNS: Novel Methods to Define and Characterize Morquio A Syndrome-Associated Mutations

Morquio A syndrome (MPS IVA) is a systemic lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfatase (GALNS), encoded by the GALNS gene. We studied 37 MPS IVA patients and defined genotype-phenotype correlations based on clinical data, biochemical assays, molecular analyses, and in silico structural analyses of associated mutations. We found that standard sequencing procedures, albeit identifying 14 novel small GALNS genetic lesions, failed to characterise about 15% of the patients' GALNS alleles. To address this drawback and uncover potential gross GALNS rearrangements we developed molecular procedures [CNVs (copy number variation assays), QF- PCRs (quantitative fluorescent- PCRs)], endorsed by CGH-arrays. Using this approach, we characterized two new large deletions and their corresponding breakpoints. Both deletions were heterozygous and included the first exon of the PIEZO1 gene, which is associated with dehydrated hereditary stomatocitosis, an autosomal dominant syndrome. In addition, we characterized the new GALNS intronic lesion c.245-11C>G causing m-RNA defects although identified outside the GT/AG splice pair. We estimated the occurrence of the disease in the Italian population to be approximately 1:300000 live births and defined a molecular testing algorithm designed to help diagnosing MPS IVA and foreseeing disease progression. This article is protected by copyright. All rights reserved.