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

Abstract

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 IV A 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 characterize the second disease-causing mutation in the 16% of the patients' cohort. To address this drawback and uncover potential gross GALNS rearrangements, we developed molecular procedures (CNV [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 1:300,000 live births and defined a molecular testing algorithm designed to help diagnosing MPS IVA and foreseeing disease progression.

Molecular diagnosis of patients affected by mucopolysaccharidosis: a multicenter study

“…(Gly290Ser)–[59]Likely pathogenicc.1043C>Ap. (Thr348Asn)–[14]Likely pathogenicc.1156C>Tp. (Arg386Cys)rs118204437; ClinVar ID:700[43]Likely pathogenicc.1219A>Cp.…”

“…(Lys503Valfs*226)–[14]Likely pathogenicc.1519T>Cp. (Cys507Arg)–[14]Likely pathogenicc.1520G>Tp. (Cys507Phe)ClinVar ID:93169[40]Not enough evidenceNC_000016.9: g.88836836_88899132del62296––[14]Likely pathogenicc.1002+307G>C––[15]Not enough evidence GLB1 (NM_000404.3; NP_000395.2)Single nucleotide variationMissense variant–Novel; Morrone A et al in publication–c.817_818delinsCTp.…”

“…(Cys507Arg)–[14]Likely pathogenicc.1520G>Tp. (Cys507Phe)ClinVar ID:93169[40]Not enough evidenceNC_000016.9: g.88836836_88899132del62296––[14]Likely pathogenicc.1002+307G>C––[15]Not enough evidence GLB1 (NM_000404.3; NP_000395.2)Single nucleotide variationMissense variant–Novel; Morrone A et al in publication–c.817_818delinsCTp. (Trp273Leu)–[44]Likely pathogenicc.1480-2A>G–rs587776526; ClinVar ID: 946[39]Pathogenic ARSB (NM_000046.4; NP_000037.2)c.245T>Cp.…”

Mucopolysaccharidosis type IVA (Morquio A): a close differential diagnosis of spondylo-epiphyseal dysplasia

“…Birth prevalence of MPS IVA ranges from 1 per 71 000 to 1 per 500 000 according to reports from several countries including Australia, Brazil, Canada, Germany, Japan, Netherlands, Saudi Arabia, Taiwan, United Arab Emirates and UK 3. A German study estimated the incidence of MPS IVA at 1 per 270 0004 whereas, in Italy, the incidence has been estimated at 1 per 300 000 live births 5…”

Estudo genético-clínico das displasias esqueléticas, com enfoque nas osteocondrodisplasias com acometimento do esqueleto axial, associado ao envolvimento epifisário e/ou metafisário

“…São características típicas o encurtamento dos ossos longos com alargamento metafisário, a hipoplasia de tórax e ilíaco, o avanço de idade óssea nos ossos do carpo e tarso, e os núcleos de ossificação adicional nas mãos com falange em delta (Huber et al, 2009 processo odontóide e alterações da epífise femural proximal. Na forma clássica, o início dos sintomas ocorre antes dos 3 anos e a estatura final encontra-se abaixo dos 120 cm, com redução da taxa de crescimento aos 18 meses de vida (Caciotti et al, 2015). Existem mais de 275 mutações diferentes relacionadas com a MPS-IVA, sendo portanto, uma explicão plausível para a variabilidade fenotípica da doença.…”