Characterization of a novel loss-of-function mutation of PAX8 associated with congenital hypothyroidism

• Published in: Clinical endocrinology (Oxford) 2010-12, Vol.73 (6), p.808-814
• Main Authors: Di Palma, Tina, Zampella, Emilia, Filippone, Maria Grazia, Macchia, Paolo Emidio, Ris-Stalpers, Carrie, De Vroede, Monique, Zannini, Mariastella
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Blotting, Western; Congenital Hypothyroidism - genetics; Disease transmission; DNA; Electrophoretic mobility; Endocrine diseases; Endocrinopathies; Expression vectors; Female; Fundamental and applied biological sciences. Psychology; Glutamine; haploinsufficiency; HeLa Cells; Histidine; Humans; Hypoplasia; Hypothyroidism; Infant, Newborn; Male; Medical sciences; Mutation; Neonates; Non tumoral diseases. Target tissue resistance. Benign neoplasms; Organogenesis; Paired Box Transcription Factors - genetics; Paired Box Transcription Factors - metabolism; Pax8 gene; Pax8 protein; PAX8 Transcription Factor; Promoters; Thyroglobulin; Thyroid; Thyroid. Thyroid axis (diseases); Transcription factors; Vertebrates: endocrinology; Young Adult
• ISSN: 0300-0664; 1365-2265
• DOI: 10.1111/j.1365-2265.2010.03851.x

Summary Background  Congenital hypothyroidism (CH) is a common endocrine disease that occurs in about 1:3000 newborns. In 80–85% of the cases, CH is presumably secondary to thyroid dysgenesis (TD), a defect in the organogenesis of the gland leading to an ectopic (30–45%), absent (agenesis, 35–40%) or hypoplastic (5%) thyroid gland. The pathogenesis of TD is still largely unknown. Most cases of TD are sporadic, although familial occurrences have occasionally been described. Recently, mutations in the PAX8 transcription factor have been identified in patients with TD. Objective  Our aim was to identify and functionally characterize novel PAX8 mutations with autosomal dominant transmission responsible for TD. Design  The PAX8 gene was sequenced in a mother and child both suffering from congenital hypothyroidism (CH) because of thyroid hypoplasia. Subsequently, expression vectors encoding the mutated PAX8 were generated, and the effects of the mutation on both the DNA‐binding capability and the transcriptional activity were evaluated. Results  PAX8 gene sequencing revealed a heterozygous mutation that consists of the substitution of a histidine residue with a glutamine at position 55 of the PAX8 protein (H55Q). When tested in cotransfection experiments with a thyroglobulin promoter reporter construct, the mutant protein turned out to be still able to bind DNA in Electrophoretic Mobility Shift Assay assays but transcriptionally inactive. Conclusions  Our findings confirm the important role of PAX8 in normal thyroid development and support the evidence that in humans haploinsufficiency of PAX8 is associated with TD.