Biallelic Stop Codon Mutations (p.F353Pfs*36/p.Y425X) in <em>DUOX2</em> Gene Associated with Transient Congenital Hypothyroidism: Report of a Family and Literature Review

Research Article

Annals Thyroid Res. 2016; 2(2): 69-78.

Biallelic Stop Codon Mutations (p.F353Pfs*36/p.Y425X) in DUOX2 Gene Associated with Transient Congenital Hypothyroidism: Report of a Family and Literature Review

Fiorella S Belforte¹, María Cecilia Olcese¹, Sofia Siffo¹, Patricia Papendieck², Rosa Enacan², Laura Grueiro-Papendieck², Ana Chiesa², Héctor M Targovnik¹ and Carina M Rivolta¹*

¹Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Argentina

²División de Endocrinología, Hospital de Nios “Ricardo Gutierrez”, Argentina

*Corresponding author: Carina M Rivolta, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Inmunología, Genética y Metabolismo (INIGEM), Facultad de Farmacia y Bioquímica, Hospital de Clínicas “José de San Martín”, Av. Córdoba 2351, Cuarto Piso, Sala 5, C1120AAR - Buenos Aires, Argentina

Received: October 03, 2016; Accepted: October 14, 2016; Published: November 03, 2016


Purpose: DUOX2 deficiency is a transient or permanent disorder that results in thyroid dyshormonogenesis. The purpose of this study was to identify and characterize new mutations in the DUOX2 gene in an attempt to increase the understanding of genotype-phenotype correlation for this disorder. The current study summarizes also the spectrum of DUOX2 variations reported to date in the literature.

Methods: Two siblings from an nonconsanguineous family with clinical and biochemical criteria suggestive of transient CH were studied. Single-Strand Conformation Polymorphism (SSCP) analysis and sequencing of DNA of TPO and DUOX2 genes were performed.

Results: Sequencing analysis of DUOX2 gene revealed two inactivating mutations, a novel c.1057_1058delTT mutation (p.F353Pfs*36, father’s mutation) and a possible previously reported c.1275T>G mutation (p.Y425X, mother’s mutation). Consequently, the two siblings carry a compound heterozygous for p.F353Pfs*36/ p.Y425X mutations, whereas the healthy brother is heterozygous for the c.1275T>G mutation and does not carry the c.1057_1058delTT mutation. Up to date, hundred twenty pathogenic variations and functional single nucleotide polymorphisms in the human DUOX2 gene have been reported associated with transient or permanent CH: 78 missense mutations, 11 nonsense mutations, 26 deletions and insertions, and 6 splice site mutations. The transient or persistent variability of the CH phenotype is not directly related to the number of mutant DUOX2 alleles. Pathogenic DUOX2 mutations were identified together with likely pathogenic variants in the TSHR, DUOXA2, Thyroid peroxidase, Thyroglobulin and SLC26A4 genes.

Conclusion: In the present study, we have identified a novel p.F353Pfs*36 mutation in peroxidase like domain of DUOX2 and we have confirmed that total loss of DUOX2 activity by biallelic premature termination codon causes transient CH phenotype.

Keywords: Congenital hypothyroidism; DUOX2 gene; Mutation; Compound heterozygous mutations; Premature stop codon


Iodide Organification Defects (IOD) associated with mutations in the TPO (Thyroid Peroxidase), SLC26A4 (solute carrier family 26 member 4, pendrin), DUOX2 (Dual Oxidasa 2) or DUOXA2 (DUOX maturation factor 2) genes are implicated in the pathogenesis of Congenital Hypothyroidism (CH) [1]. IOD is characterized by high levels of serum TG and TSH with simultaneous low levels of circulating thyroid hormones and a positive Perchlorate Descarge Test (PDT), indicating that the iodide is taken up by thyroid cells but it is not incorporated into the TG protein [1,2].

The key enzymatic system involved in the iodide organification process is located on the apical plasma membrane of polarized follicular thyroid cells. TPO catalyzes both the iodination and coupling of hormonogenic tyrosyl residues of TG with an absolute requirement of hydrogen peroxide, which acts as an electron acceptor [3]. H2O2 is generated by a metabolic pathway, involving DUOX1 and DUOX2 [3-5].

PDT is used to distinguish Total Iodide Organification Defect (TIOD) from Partial Thyroid Organification Defect (PIOD). TPO gene mutations in patients with PIOD usually affect a single allele, whereas homozygous or compound-heterozygous TPO mutations are associated to TIOD [1]. Mutations in SLC26A4 gene cause Pendred syndrome characterized by congenital sensorineural hearing loss, goiter with or without hypothyroidism and usually PIOD [1]. Most of patients with mutations in DUOX2 gene are characterized by PIOD. Furthermore, mutations in DUOX2 gene have been associated to transient CH (TCH) or permanent CH (PCH), with a high intra and interfamilial phenotypic variability [2]. Instead, TCH can be caused by iodine excess or deficiency and exposure to maternal antithyroid drugs or transplacental antibodies [6,7]. PCH requires lifelong thyroid hormone replacement.

Most cases of CH associated with alterations in the DUOX2 are caused by either biallelic or monoallelic mutations which lead to relantionships between DUOX2 genotypes and clinical phenotypes extremaly complex [8-10]. Both biallelic and monoallelic DUOX2 mutations could be associated with TCH or PCH [11,12]. Because DUOX2 biallelic mutations commonly are inherited in an autosomal recessive manner, the patients should be homozygous or compound heterozygous for gene mutations and the parents should be carriers of one DUOX2 mutation. Up to date, 121 variations have been identified and characterized throughout the DUOX2 gene [8,9,11-13-47].

In the present study we report a family with transient CH. Screening of DUOX2 gene revealed two inactivating mutations, a novel c.1057_1058delTT mutation (p.F353Pfs*36) and a possible previously documented c.1275T>G mutation (p.Y425X) [19], conforming a new compound heterozygous. Remarkable, as our findings confirm, severe biallelic defects of DUOX2 in transient CH infers compensatory mechanisms in the peroxide supply.

Materials and Methods


We report 2 siblings of nonconsanguineous healthy parents and affected with congenital hypothyroidism which led to perform genetic testing.

The proband (II-1), born in 2003, was a girl who was detected through neonatal screening with elevated TSH, 32.5 mUI/l blood at 2 days of life (Cut of <10 mUI/L). Thyroid profile at 1 month of age showed TSH: 32 mU/L (reference range: <10), TT4 13 ug/dl, (reference range 6-18) FT4: 1.46 ng/dl (reference range:1-2.6) and TG: 266 ng/ dl (reference range: 30-100) with no circulating autoantibodies (anti- TPO and anti-TG) (Table 1) and eutopic enlarged thyroid gland in the 99mTc scan. These results suggested a defect in thyroid hormone synthesis and so treatment with levothyroxine was started at 25 μg per day and continued since 2.9 years of age. At that time treatment was discontinued for a month in order to reevaluate her thyroid function. Serum TSH, TT4 and FT4 levels were normal and TG slightly elevated (Table 1). A Perchlorate discharge test was performed with 17% of discharge (normal <15%). Thyroid ultrasound was normal. Treatment was restarted and stopped again for a month at 7 years of age. Thyroid profile was normal (Table 1), perchlorate test negative and TG: 51.2 ng/dl (reference range: 6-40). Therefore levothyroxine replacement was not necessary. She is now 12 years old, grows normally, has an adequate school performance, undergoes normal puberty and keeps euthyroid.