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


METHODS
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.
Di Palma
Tina
T
IEOS, G. Salvatore National Research Council, Naples, Italy.
Zampella
Emilia
E
Filippone
Maria Grazia
MG
Macchia
Paolo Emidio
PE
Ris-Stalpers
Carrie
C
de Vroede
Monique
M
Zannini
Mariastella
M
D000328:Adult; D015153:Blotting, Western; D003409:Congenital Hypothyroidism / Q000235:genetics*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009154:Mutation; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics* / Q000378:metabolism; D055815:Young Adult
D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors