The Relationship Between Iodine Status and Thyroid Function in Congenital Hypothyroidism With Eutopic Thyroid Gland

Background: We investigated the relationship between iodine status and thyroid function in children with congenital hypothyroidism (CH) with eutopic gland. We also evaluated whether the presence of iodine organification defect (IOD) or pathogenic genetic variants affects the association between iodine status and thyroid function. Methods: A total of 31 children (14 boys) with CH participated in the study, who repeatedly underwent thyroid function test and urine iodine concentration (UIC) without levothyroxine (LT4) medication after 3 years of age (1-5 times per patient). After confirming eutopic gland, IOD was demonstrated by the positive perchlorate discharge test with a discharge rate >10%. Genetic analysis was performed using targeted gene sequencing including 23 genes. Results: We identified likely pathogenic or pathogenic variants in 14 cases (45.2%): 1 case with triallelic (digenic) variants (DUOX2 and TSHR), 4 cases with biallelic variants (3 DUOX2 and 1 TSHR), and 9 cases with monoallelic variants (7 DUOX2, 1 DUOXA2, and 1 TSHR). Among 26 cases treated with LT4 from neonatal period, thyroid function after LT4 discontinuation was euthyroid (n = 7), subclinically hypothyroid (n=15), and overtly hypothyroid requiring LT4 (n = 3). The other 5 cases without LT4 treatment remained subclinical hypothyroid. After excluding 2 cases with TSHR, 29 cases (with 72 samples) were included to analyze the relationship between iodine status and log-transformed TSH (log-TSH) using generalized estimating equation models. The positive IOD (n = 17) was not associated with presence of DUOX2/DUOXA2 variants (n = 12). Iodine status of urine samples was categorized into adequate (UIC < 300 μg/L, n = 25), mild excessive (UIC = 300-599 μg/L, n = 14), and severe excessive (UIC ≥ 600 μg/L, n = 33) groups. When stratified by the presence of IOD, log-TSH significantly increased in severe excessive group (β = 0.52, P = 0.014 vs. iodine adequate group) among negative IOD group, but rather decreased in mild excessive group (β = -0.84, P < 0.001 vs. iodine adequate group) among positive IOD group. Meanwhile, when stratified by the presence of DUOX2/DUOXA2 variants, no significant association was found between iodine status and log-TSH levels. Conclusion:DUOX2 mutation was most common in CH patients with eutopic gland. The relationship of iodine status with thyroid function differed by presence of IOD.

Clinical and laboratory features of children and adolescents with congenital hypothyroidism due to dyshormonogenesis in southern Brazil

OBJECTIVE: To characterize the phenotype of patients with congenital hypothyroidism (CH) due to dyshormonogenesis, and to hypothesize on the degree of genetic defect. SUBJECTS AND METHODS: Patients with dyshormonogenesis were subdivided into G1 (radioactive iodine uptake, RAIU > 15%; n = 62) and G2 (RAIU < 15%; n = 32). Thyroglobulin (TG) was measured in all patients; perchlorate discharge test (PDT) was performed in G1; and saliva-to-plasma radioiodine ratio (I- S/P) in G2. RESULTS: Levels of TSH, TT4, and FT4 before treatment and upon diagnosis confirmation were significantly different in both groups, but not between groups. In G1, 27 patients developed goiter; 17 had positive PDT (14%-71% discharge), 11 had TG < 2.5 ng/dL (one with high TSH), and one developed thyroid carcinoma. In G2, four patients developed goiter, and three had low I- S/P. CONCLUSION: These data suggest an iodide organification defect in 17 cases; an iodide transport defect (NIS defect) in three, probable TSH resistance in 10, and a TG synthesis defect in two cases.

Monoallelic thyroid peroxidase gene mutation in a patient with congenital hypothyroidism with total iodide organification defect

The aim of this study was to identify the genetic defect of a patient with dyshormonogenetic congenital hypothyroidisms (CH) with total iodide organification defect (TIOD). A male child diagnosed with CH during neonatal screening. Laboratory tests confirmed the permanent and severe CH with TIOD (99% perchlorate release). The coding sequence of TPO, DUOX2, and DUOXA2 genes and 2957 base pairs (bp) of the TPO promoter were sequenced. Molecular analysis of patient's DNA identified the heterozygous duplication GGCC (c.1186_1187insGGCC) in exon 8 of the TPO gene. No additional mutation was detected either in the TPO gene, TPO promoter, DUOX2 or DUOXA2 genes. We have described a patient with a clear TIOD causing severe goitrous CH due to a monoallelic TPO mutation. A plausible explanation for the association between an autosomal recessive disorder with a single TPO-mutated allele is the presence of monoallelic TPO expression.

Pendred Syndrome in a large consanguineous Brazilian family caused by a homozygous mutation in the SLC26A4 gene

Pendred Syndrome (PS) is an autossomal recessive disorder characterized by sensorineural deafness, goiter and iodide organification defect. The hearing loss is associated with inner ear abnormalities, ranging from an isolated enlarged vestibular aqueduct (EVA) to a typical coclear dysplasia. Mutations in the gene that encodes pendrin (SLC26A4), a chloride/iodide transporter, have been shown to be associated with PS. We describe the clinical and molecular characteristics of a large consanguineous family harboring a mutation in the SLC26A4 gene. The proband was a 26-year-old deaf Brazilian woman who presented a bulky multinodular goiter and hypothyroidism since puberty. Five other siblings were deaf: one brother had a similar phenotype, three siblings also had goiters but normal thyroid function tests, and one brother had only a subtle thyroid enlargement. Other 4 siblings had no thyroid or hearing disorder. Parents were first degree cousins and had normal hearing. The mother was healthy, except for subclinical hypothyroidism; the father was deceased. A perchlorate test in the proband showed a discharge of 21% of the incorporated iodide 2h after the administration of 1g of KClO4. Audiological examinations showed profound hearing loss in all deaf subjects; CT and MRI of the temporal bones showed EVA in all of them. Genomic DNA was isolated from whole blood, from the 6 affected and 4 unaffected siblings, the mother and control. The coding region of the PDS gene (exons 2-21), including exon/intron boundaries, were amplified by PCR and sequenced. A single base-pair (T) deletion at position 1197 of exon 10 was detected in homozygous state in the 6 deaf siblings. The mother and 2 unaffected siblings were heterozygous for this mutation, which has been described by Everett et al. The 1197delT mutation is predicted to result in a frameshift and a truncated protein. The existence of PS phenocopies and intrafamilial phenotypic variability are well documented. The definite diagnosis requires molecular analysis. Our study illustrates the value and challenges of mutational analysis in selected patients with PS.

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

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.