Heterozygous Mutations of the DUOXA2 and DUOX2 Genes in Dizygotic Twins with Congenital Hypothyroidism

Background: The mutations in the dual oxidase maturation factor 2 (DUOXA2) and dual oxidase 2 (DUOX2) genes have been identified in patients with congenital hypothyroidism (CH). This study reports a set of dizygotic twins with CH due to the mutations in the DUOX2/DUOXA2 system. Methods: The dizygotic twins, a boy and a girl, both aged 7 years, were born to euthyroid nonconsanguineous parents; they were diagnosed with CH at neonatal screening and were enrolled in this study. The DUOXA2, DUOX2, paired box 8 (PAX8), thyroid peroxidase (TPO), and thyrotropin receptor (TSHR) genes were considered for mutation screening. Genomic DNA was extracted from peripheral blood leukocytes, and Sanger sequencing was used to screen for the mutations in the exon fragments. Family members of the patients were also enrolled and evaluated. Results: The fraternal twins each harbored a single heterozygous mutation, including c.738C>G (p.Y246X) in the boy inherited from the paternal DUOXA2 allele and c.2654G>A (p.R885Q) in the girl from the maternal DUOX2 allele. The two mutations have been previously reported. The boy showed enlarged thyroid lobes and a little calcification in the left lobe, while the girl's thyroid gland was severely underdeveloped and the girl had obvious complications due to irregular treatment. The germline mutations from this family were consistent with an autosomal recessive inheritance pattern. No mutations in the PAX8, TPO, and TSHR genes were detected in this study. Conclusions: The inactivating mutations in the DUOXA2 (p.Y246X) and DUOX2 (p.R885Q) genes were identified in a set of dizygotic twins with CH. The girl was more severe in several aspects than her brother. The similar genetic defect resulted in very different outcomes.