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Case Reports
. 2018 Oct 11;19(1):183.
doi: 10.1186/s12881-018-0694-6.

Mis-splicing of the GALNS gene resulting from deep intronic mutations as a cause of Morquio a disease

Anna Caciotti  1 , Rodolfo Tonin  1   2 , Matthew Mort  3 , David N Cooper  3 , Serena Gasperini  4 , Miriam Rigoldi  4 , Rossella Parini  4 , Federica Deodato  5 , Roberta Taurisano  5 , Michelina Sibilio  6 , Giancarlo Parenti  6 , Renzo Guerrini  1   2 , Amelia Morrone  7   8
Affiliations
Case Reports

Mis-splicing of the GALNS gene resulting from deep intronic mutations as a cause of Morquio a disease

Anna Caciotti et al. BMC Med Genet. .

Abstract

Background: Mucopolysaccharidosis-IVA (Morquio A disease) is a lysosomal disorder in which the abnormal accumulation of keratan sulfate and chondroitin-6-sulfate is consequent to mutations in the galactosamine-6-sulfatase (GALNS) gene. Since standard DNA sequencing analysis fails to detect about 16% of GALNS mutant alleles, gross DNA rearrangement screening and uniparental disomy evaluation are required to complete the molecular diagnosis. Despite this, the second pathogenic GALNS allele generally remains unidentified in ~ 5% of Morquio-A disease patients.

Methods: In an attempt to bridge the residual gap between clinical and molecular diagnosis, we performed an mRNA-based evaluation of three Morquio-A disease patients in whom the second mutant GALNS allele had not been identified. We also performed sequence analysis of the entire GALNS gene in two patients.

Results: Different aberrant GALNS mRNA transcripts were characterized in each patient. Analysis of these transcripts then allowed the identification, in one patient, of a disease-causing deep intronic GALNS mutation. The aberrant mRNA products identified in the other two individuals resulted in partial exon loss. Despite sequencing the entire GALNS gene region in these patients, the identity of a single underlying pathological lesion could not be unequivocally determined. We postulate that a combination of multiple variants, acting in cis, may synergise in terms of their impact on the splicing machinery.

Conclusions: We have identified GALNS variants located within deep intronic regions that have the potential to impact splicing. These findings have prompted us to incorporate mRNA analysis into our diagnostic flow procedure for the molecular analysis of Morquio A disease.

Keywords: Deep intronic mutations; GALNS; Morquio a disease; Mucopolysaccharidosis IVA; Whole gene sequencing; mRNA defects.

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Conflict of interest statement

Ethics approval and consent to participate

According to local ethical guidelines, all nucleic acid samples were obtained for storage and analysis only after the patients’ family members’ written informed consent had been obtained, using a form approved by the local Ethics Committee (Ethics Committee of the Meyer Hospital, Florence, Italy).

Consent for publication

The patients’ family members’ written informed consents contain their permission to publish patient data.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Diagnostic flowchart for Morquio A disease. The flowchart illustrates our clinical/laboratory analytical procedure. It should be noted that the procedure includes mRNA analysis in addition to DNA and protein analysis
Fig. 2
Fig. 2
Aberrant splicing products detected in Morquio A patients in the heterozygous state. The alternative GALNS cDNA (RT-PCR) products were detected in samples from: a Pt3; b, c Mother of Pt3; d Pt3 and his father; e Pt2; f Pt1. Ten normal controls were included alongside the three patients in the mRNA analyses in order to compare the GALNS cDNA amplification products. The control group did not show any aberrant transcripts. Del, deletion; ins, insertion; trunc, truncated; ex, exon
See this image and copyright information in PMC

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