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Biallelic Inactivation of the Dual Oxidase Maturation Factor 2 (DUOXA2) Gene as a Novel Cause of Congenital Hypothyroidism

Laboratory of Pediatric Endocrinology (I.Z., S.M.), Department of Pediatrics (F.C., M.C.V., G.C., S.M., G.W.), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, and Department of Medical Sciences (L.F., L.P.), University of Milan, Istituto Auxologico Italiano (L.P.) and Fondazione Ospedale Maggiore Policlinico (L.F.), 20100 Milan, Italy; and Departments of Medicine (H.G., K.O., S.R.) and Pediatrics (S.R.) and Committee on Genetics (S.R.), University of Chicago, Chicago, Illinois 60637

Address all correspondence and requests for reprints to: Luca Persani, M.D., Ph.D., Department of Medical Sciences, University of Milan, Lab of Experimental Endocrinology, Istituto di Ricovero e Cura a Carattere Scientifico, Istituto Auxologico Italiano, Via Zucchi 18, 20095 Cusano (Milan), Italy. E-mail: luca.persani{at}unimi.it.

Context: Dual oxidase 2 (DUOX2) is the catalytic core of the H₂O₂ generator crucial for the iodination of thyroglobulin in thyroid hormone synthesis. DUOX2 deficiency produces congenital hypothyroidism (CH) in humans and mice. We recently cloned a novel gene, the product of which (dual oxidase maturation factor 2; DUOXA2) is required to express DUOX2 enzymatic activity.

Objective: Our objective was to identify DUOXA2 mutations as a novel cause of CH due to dyshormonogenesis.

Patients: Subjects included 11 CH patients with partial iodine organification defect but negative for other known genetic causes of partial iodine organification defect.

Results: One Chinese patient born to nonconsanguineous parents was homozygous for a nonsense mutation (p.Y246X), producing a truncated DUOXA2 protein lacking transmembrane helix 5 and the C-terminal cytoplasmic domain. The mutant protein was inactive in reconstituting DUOX2 in vitro. Pedigree analysis demonstrated recessive inheritance, because heterozygous carriers had normal thyroid function including negative results in neonatal TSH screening. One heterozygous carrier of Y246X was identified in unrelated Chinese controls (n = 92) but not in Caucasian or Japanese controls, indicating that homozygosity for Y246X could be a frequent cause of CH in Chinese. Functional studies suggest that the DUOXA2 paralog (DUOXA1) can partially compensate DUOXA2 deficiency, consistent with the proband having a milder CH phenotype than patients with biallelic DUOX2 nonsense mutations.

Conclusions: We report the first mutation in DUOXA2, identified in a patient with CH and dyshormonogenic goiter. Results of our studies provide evidence for the critical role of DUOXA2 in thyroid hormonogenesis. Biallelic DUOXA2 mutations are a novel genetic event in permanent CH.