Solving a case of allelic dropout in the GNPTAB gene: implications in the molecular diagnosis of mucolipidosis type III alpha/beta

Coutinho, Maria Francisca; Encarnação, Marisa; Laranjeira, Francisco; Lacerda, Lúcia; Prata, Maria João; Alves, Sandra

http://hdl.handle.net/10400.18/4286

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Authors

Coutinho, Maria Francisca

Encarnação, Marisa

Laranjeira, Francisco

Lacerda, Lúcia

Prata, Maria João

Alves, Sandra

Abstract(s)

While being well known that the diagnosis of many genetic disorders relies on a combination of clinical suspicion and confirmatory genetic testing, not rarely, however, genetic testing needs much perseverance and cunning strategies to identify the causative mutation(s). Here we present a case of a thorny molecular diagnosis of mucolipidosis type III alpha/beta, which is an autosomal recessive lysosomal storage disorder, caused by a defect in the GNPTAB gene that codes for the α/β-subunits of the GlcNAc-1-phosphotransferase. We used both cDNA and gDNA analyses to characterize a mucolipidosis type III alpha/beta patient whose clinical diagnosis was already confirmed biochemically. In a first stage only one causal mutation was identified in heterozygosity, the already described missense mutation c.1196C>T(p.S399F), both at cDNA and gDNA levels. Only after conducting inhibition of nonsense-mediated mRNA decay (NMD) assays and after the utilization of another pair of primers the second mutation, the c.3503_3504delTC deletion, was identified. Our findings illustrate that allelic dropout due to the presence of polymorphisms and/or of mutations that trigger the NMD pathway can cause difficulties in current molecular diagnosis tests.

Keywords

Allelic Dropout Genotype-phenotype Correlation GlcNAc-1-phosphotransferase GNPTAB ML III alpha/beta Molecular Genetic Testing Nonsense Mediated mRNA Decay Polymorphism Doenças Genéticas