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Buried in the Middle but Guilty: Intronic Mutations in the TCIRG1 Gene Cause Human Autosomal Recessive Osteopetrosis
Author(s) -
Palagano Eleonora,
Blair Harry C,
Pangrazio Alessandra,
Tourkova Irina,
Strina Dario,
Angius Andrea,
Cuccuru Gianmauro,
Oppo Manuela,
Uva Paolo,
Van Hul Wim,
Boudin Eveline,
SupertiFurga Andrea,
Faletra Flavio,
Nocerino Agostino,
Ferrari Matteo C,
Grappiolo Guido,
Monari Marta,
Montanelli Alessandro,
Vezzoni Paolo,
Villa Anna,
Sobacchi Cristina
Publication year - 2015
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.2517
Subject(s) - osteopetrosis , tcirg1 , exome sequencing , genetics , biology , exon , rna splicing , intron , exome , alternative splicing , mutation , splice site mutation , gene , genetic heterogeneity , phenotype , rna , immunology , cytotoxic t cell , antigen presenting cell , in vitro
Autosomal recessive osteopetrosis (ARO) is a rare genetic bone disease with genotypic and phenotypic heterogeneity, sometimes translating into delayed diagnosis and treatment. In particular, cases of intermediate severity often constitute a diagnostic challenge and represent good candidates for exome sequencing. Here, we describe the tortuous path to identification of the molecular defect in two siblings, in which osteopetrosis diagnosed in early childhood followed a milder course, allowing them to reach the adult age in relatively good conditions with no specific therapy. No clearly pathogenic mutation was identified either with standard amplification and resequencing protocols or with exome sequencing analysis. While evaluating the possible impact of a 3'UTR variant on the TCIRG1 expression, we found a novel single nucleotide change buried in the middle of intron 15 of the TCIRG1 gene, about 150 nucleotides away from the closest canonical splice site. By sequencing a number of independent cDNA clones covering exons 14 to 17, we demonstrated that this mutation reduced splicing efficiency but did not completely abrogate the production of the normal transcript. Prompted by this finding, we sequenced the same genomic region in 33 patients from our unresolved ARO cohort and found three additional novel single nucleotide changes in a similar location and with a predicted disruptive effect on splicing, further confirmed in one of them at the transcript level. Overall, we identified an intronic region in TCIRG1 that seems to be particularly prone to splicing mutations, allowing the production of a small amount of protein sufficient to reduce the severity of the phenotype usually associated with TCIRG1 defects. On this basis, we would recommend including TCIRG1 not only in the molecular work‐up of severe infantile osteopetrosis but also in intermediate cases and carefully evaluating the possible effects of intronic changes. © 2015 American Society for Bone and Mineral Research.