Genetic analysis in children with transient thyroid dysfunction or subclinical hypothyroidism detected on neonatal screening

Guidelines for Newborn Screening of Congenital Hypothyroidism (2021 Revision)

Purpose of developing the guidelines: Newborn screening (NBS) for congenital hypothyroidism (CH) was started in 1979 in Japan, and early diagnosis and treatment improved the intelligence prognosis of CH patients. The incidence of CH was once about one in 5,000-8,000 births, but has been increased with diagnosis of subclinical CH. The disease requires continuous treatment and specialized medical facilities should conduct differential diagnosis and treatment in patients who are positive by NBS to avoid unnecessary treatment. The Guidelines for Mass Screening of Congenital Hypothyroidism (1998 version) were developed by the Mass Screening Committee of the Japanese Society for Pediatric Endocrinology in 1998. Subsequently, the guidelines were revised in 2014. Here, we have added minor revisions to the 2014 version to include the most recent findings. Target disease/conditions: Primary congenital hypothyroidism. Users of the Guidelines: Physician specialists in pediatric endocrinology, pediatric specialists, physicians referring pediatric practitioners, general physicians, laboratory technicians in charge of mass screening, and patients.

Curating the gnomAD database: Report of novel variants in the thyroid peroxidase gene using in silico bioinformatics algorithms and a literature review

Thyroid peroxidase (TPO) is a membrane-bound glycoprotein located at the apical side of the thyroid follicular cells that catalyzes both iodination and coupling of iodotyrosine residues within the thyroglobulin molecule, leading to the synthesis of thyroid hormone. Variants in TPO cause congenital hypothyroidism (CH) by iodide organification defect and are commonly inherited in an autosomal recessive fashion. In the present work, we report a detailed population analysis and bioinformatic prediction of the TPO variants indexed in the Genome Aggregation Database (gnomAD) v2.1.1. The proportion of missense cysteine variants and nonsense, frameshift, and splice acceptor/donor variants were analyzed in each ethnic group (European (Non-Finnish), European (Finnish), African/African Americans, Latino/Admixed American, East Asian, South Asian, Ashkenazi Jewish, Other). The results showed a clear predominance of frameshift variants in the East Asian (82%) and European (Finnish) (75%) population, whereas the splice site variants predominate in African/African Americans (99.46%), Other (96%), Latino/Admixed American (94%), South Asian (86%), European (Non-Finnish) (56%) and Ashkenazi Jewish (56%) populations. The analysis of the distribution of the variants indexed in gnomAD v2.1.1 database revealed that most missense variants identified in the An peroxidase domain map in exon 8, followed by exons 11, 7 and 9, and finally in descending order by exons 10, 6, 12 and 5. In total, 183 novel TPO variants were described (13 missense cysteine's variants, 158 missense variants involving the An peroxidase domain and 12 splicing acceptor or donor sites variants) which were not reported in the literature and that would have deleterious effects on prediction programs. In the gnomAD v2.1.1 population, the estimated prevalence of heterozygous carriers of the potentially damaging variants was 1:77. In conclusion, we provide an updated and curated reference source of new TPO variants for application in clinical diagnosis and genetic counseling. Also, this work contributes to elucidating the molecular basis of CH associated with TPO defects.

Update on Neonatal Isolated Hyperthyrotropinemia: A Systematic Review

The purpose of this paper was to systematically summarize the published literature on neonatal isolated hyperthyrotropinemia (HTT), with a focus on prevalence, L-T4 management, re-evaluation of thyroid function during infancy or childhood, etiology including genetic variation, thyroid imaging tests, and developmental outcome. Electronic and manual searches were conducted for relevant publications, and a total of 46 articles were included in this systematic review. The overall prevalence of neonatal HTT was estimated at 0.06%. The occurrence of abnormal imaging tests was found to be higher in the persistent than in the transient condition. A continuous spectrum of thyroid impairment severity can occur because of genetic factors, environmental factors, or a combination of the two. Excessive or insufficient iodine levels were found in 46% and 16% of infants, respectively. Thirty-five different genetic variants have been found in three genes in 37 patients with neonatal HTT of different ethnic backgrounds extracted from studies with variable design. In general, genetic variants reported in the TSHR gene, the most auspicious candidate gene for HTT, may explain the phenotype of the patients. Many practitioners elect to treat infants with HTT to prevent any possible adverse developmental effects. Most patients with thyroid abnormalities and/or carrying monoallelic or biallelic genetic variants have received L-T4 treatment. For all those neonates on treatment with L-T4, it is essential to ensure follow-up until 2 or 3 years of age and to conduct medically supervised trial-off therapy when warranted. TSH levels were found to be elevated following cessation of therapy in 44% of children. Withdrawal of treatment was judged as unsuccessful, and medication was restarted, in 78% of cases. Finally, data extracted from nine studies showed that none of the 94 included patients proved to have a poor developmental outcome (0/94). Among subjects presenting with normal cognitive performance, 82% of cases have received L-T4 therapy. Until now, the precise neurodevelopmental risks posed by mild disease remain uncertain.

Genotype and phenotype correlation in a cohort of Chinese congenital hypothyroidism patients with DUOX2 mutations

BACKGROUND

This study aimed to explore the relationship between the phenotype and genotype of congenital hypothyroidism (CH) caused by dual oxidase 2 (DUOX2) mutation in Chinese children, and to investigate the genetic causes of permanent and transient hypothyroidism through next-generation genetic testing technology and long-term clinical follow-up data.

METHODS

We recruited 61 patients with thyroid stimulating hormone (TSH) levels of >10 mIU/mL during newborn screening, clinical diagnosis of CH, and L-thyroxine (L-T4) oral treatment within 1 month of birth; they were followed up until the present. All CH infants and their parents were genotyped using whole-exome sequencing (WES); DUOX2 variants were detected in 20 infants, and the longitudinal prognosis, genotype, and phenotype correlations were analyzed.

RESULTS

Biallelic DUOX2 mutations were detected in 20 participants. All of them were born full term. All patients were treated with L-T4 when diagnosed with CH; 9 of them stopped L-T4 eventually before 3 years old; and 2 were treated with a reduced dose of L-T4 (12.5 µg per day). The others were still treated with L-T4 at a dose of 37.5-87.5 µg per day. Of these 20 participants, 5 carried an R1110Q variant and 5 carried K530X variants. A total of 7 novel variants were discovered in our cohort. The variants carried in transient CH patients were located extracellularly and not near the functional domain.

CONCLUSIONS

Most CH patients with DUOX2 mutations were those with transient or subclinical CH. The R1110Q, R885L, and K530X were the most common variants in our Chinese cohort. The R1110Q and K530X variants may play a founder effect in the transient CH. The R885L variant may play a benign role in transient CH. Intracellular variants or those near the functional domain may cause permanent CH.

Complicated Relationship between Genetic Mutations and Phenotypic Characteristics in Transient and Permanent Congenital Hypothyroidism: Analysis of Pooled Literature Data

PURPOSE

Mutations and phenotypic characteristics remain unclear in patients with congenital hypothyroidism (CH), and no study concerning whether the outcome of transient CH (TCH) or permanent CH (PCH) is determined by mutations has been reported.

METHODS

We searched the literature up to April 2019. Eligible studies and data extraction were performed. We estimated the relationship between mutations and phenotypic characteristics in pooled patients with CH.

RESULTS

Two hundred forty-one cases were pooled from 41 eligible studies. The thyroid morphology, classification of mutated genes, and types of mutations were different between 94 patients with TCH and 147 patients with PCH. Heterozygous missense mutations prevailed in PAX8, TSHR, FOXE1, and NKX2-5, and patients with these mutated genes had a higher risk of PCH (OR = 37.38, 95% CI 5.04-277.21, P < 0.001). TCH and PCH have equal shares in patients with mutated DUOX2 or DUOXA2. Dual-site and multisite mutations were frequently detected in DUOX2. High phenotypic heterogeneity was observed in mutated DUOX2 even in the same mutations. However, there was no relationship found between mutations and transient or permanent outcome in patients with mutated DUOX2.

CONCLUSION

Transient or permanent outcomes were influenced by the biological function of mutated genes instead of types of mutations among patients with CH. Patients whose mutations were related to thyroid dysgenesis (TD) were more likely to have PCH. The relationship between mutations and phenotypic characteristics is complicated, and phenotypic characteristics may be affected by mutations and other factors.

A Population-Based Genomic Study of Inherited Metabolic Diseases Detected Through Newborn Screening

Background

A newborn screening (NBS) program has been utilized to detect asymptomatic newborns with inherited metabolic diseases (IMDs). There have been some bottlenecks such as false-positives and imprecision in the current NBS tests. To overcome these issues, we developed a multigene panel for IMD testing and investigated the utility of our integrated screening model in a routine NBS environment. We also evaluated the genetic epidemiologic characteristics of IMDs in a Korean population.

Methods

In total, 269 dried blood spots with positive results from current NBS tests were collected from 120,700 consecutive newborns. We screened 97 genes related to NBS in Korea and detected IMDs, using an integrated screening model based on biochemical tests and next-generation sequencing (NGS) called NewbornSeq. Haplotype analysis was conducted to detect founder effects.

Results

The overall positive rate of IMDs was 20%. We identified 10 additional newborns with preventable IMDs that would not have been detected prior to the implementation of our NGS-based platform NewbornSeq. The incidence of IMDs was approximately 1 in 2,235 births. Haplotype analysis demonstrated founder effects in p.Y138X in DUOXA2, p.R885Q in DUOX2, p.Y439C in PCCB, p.R285Pfs^*2 in SLC25A13, and p.R224Q in GALT.

Conclusions

Through a population-based study in the NBS environment, we highlight the screening and epidemiological implications of NGS. The integrated screening model will effectively contribute to public health by enabling faster and more accurate IMD detection through NBS. This study suggested founder mutations as an explanation for recurrent IMD-causing mutations in the Korean population.

DUOX2 Mutations Are Frequently Associated With Congenital Hypothyroidism in the Korean Population

Background

Most cases with congenital hypothyroidism (CH) are usually sporadic, while about 20% of the cases are caused by genetic defects. Little information is available regarding the mutation incidence and genetic heterogeneity of CH in Koreans. We aimed to determine the mutation incidence of CH in newborn screenings (NBS) and to evaluate the frequency and spectrum of mutations underlying CH.

Methods

A total of 112 newborns with thyroid dysfunction were enrolled from 256,624 consecutive NBS. Furthermore, 58 outpatients with primary CH were added from an endocrine clinic. All coding exons of TSHR, PAX8, TPO, DUOX2, DUOXA2, and SCL5A5 were sequenced.

Results

The mutation incidence of CH was estimated to be 1 in 6,580 newborns. A total of 36 different mutations were identified in 53 cases. The overall mutation positive rate was 31%. The DUOX2 mutations were the most prevalent in both newborns and outpatients. Seven different recurrent mutations [p.G488R (n=13), p.A649E (n=3), p.R885Q (n=3), p.I1080T (n=2), and p.A1206T (n=2) in DUOX2; p.Y138X (n=9) in DUOXA2; and p.R450H (n=5) in TSHR) were identified as the mutations underlying CH.

Conclusions

The mutation incidence of CH was considerably higher than expected in the Korean newborn population. This study revealed seven different recurrent mutations underlying CH. We conclude that DUOX2 mutations are a frequent cause of CH in the Korean population.

National survey on concepts for congenital hypothyroidism screening in neonatal intensive care units in Japan

BACKGROUND

Recently, a revised version of the Guidelines for Mass Screening of Congenital Hypothyroidism (CH) was published in Japan, but it is not known whether the guidelines are used routinely in neonatal intensive care units (NICU).

METHODS

To clarify the current status and issues of newborn screening (NBS) for CH in Japanese NICU, we sent a questionnaire by mail or email to neonatologists responsible for 100 tertiary NICU in Japan, and analyzed their responses.

RESULTS

The response rate was 92% (92/100). Among respondents, 65% (59/91) performed thyroid function testing separately from NBS for CH. Within this group, 63% (37/59) applied criteria, mostly for very low-birthweight (VLBW) infants (25/37). Only 29% of respondents (26/90), however, used criteria to select VLBW infants for treatment. Furthermore, criteria differed in each NICU. Fifty-seven percent of respondents (50/87) reported issues regarding NBS for CH in NICU, which fell into three main areas: establishment of a clear method for the management of VLBW infants; necessity of simultaneous measurement of thyroid-stimulating hormone and free thyroxine; and overlapping blood collection for NBS and thyroid function tests.

CONCLUSIONS

Two-thirds of tertiary NICU performed thyroid function testing separately from NBS for CH. Approximately 60% of neonatologists responded that current NBS for CH had ongoing issues. Further research is needed to establish the optimal NBS protocol for CH in NICU in Japan.

Transient Congenital Hypothyroidism in Turkey: An Analysis on Frequency and Natural Course

OBJECTIVE

Prevalence of congenital hypothyroidism (CH) in Turkey at birth was reported to be as high as 1:650 in 2008-2010. Incidence rates of permanent and transient CH separately are unknown due to lack of follow-up data. We aimed to evaluate the impact of transient hypothyroidism on increasing incidence of CH and to determine the natural course and the clinical, biochemical, and imaging characteristics of transient CH.

METHODS

Baseline and follow-up data of the infants with CH detected at screening in six provinces in the Black Sea Region were analyzed retrospectively during a time period covering the years 2008-2010.

RESULTS

Among 138 cases (48% female), 16 (12%) showed transient hyperthyrotropinemia which resolved without intervention. Of the treated 122 cases, 63 (52%) had transient CH. While its frequency was 35% in 2008, it increased to 56% in 2009-2010, following a lowering of the thyroid stimulating hormone cutoff value. The frequency was higher in inland provinces than in coast (67% vs. 43%; p=0.01).Clinical characteristics of permanent and transient cases were similar except female-to-male sex ratios (1.5:1 vs. 0.6:1; p=0.02). L-thyroxine was discontinued in 70% of transient cases before 3 years of age at a median age of 19 (2-36) months. The only indication for early discontinuation of treatment was a low L-thyroxine dose, which was 1.25±0.27 µg/kg/day at withdrawal time.

CONCLUSION

Our regional follow-up data showed that more than half of newborns with primary CH had transient thyroid dysfunction. In the majority of cases, discrimination between transient and permanent CH can be made before age 3 years, as indicated by cessation of L-thyroxine treatment.

Guidelines for Mass Screening of Congenital Hypothyroidism (2014 revision)

Purpose of developing the guidelines: Mass screening for congenital hypothyroidism started in 1979 in Japan, and the prognosis for intelligence has been improved by early diagnosis and treatment. The incidence was about 1/4000 of the birth population, but it has increased due to diagnosis of subclinical congenital hypothyroidism. The disease requires continuous treatment, and specialized medical facilities should make a differential diagnosis and treat subjects who are positive in mass screening to avoid unnecessary treatment. The Guidelines for Mass Screening of Congenital Hypothyroidism (1998 version) were developed by the Mass Screening Committee of the Japanese Society for Pediatric Endocrinology in 1998. Subsequently, new findings on prognosis and problems in the adult phase have emerged. Based on these new findings, the 1998 guidelines were revised in the current document (hereinafter referred to as the Guidelines). Target disease/conditions: Primary congenital hypothyroidism. Users of the Guidelines: Physician specialists in pediatric endocrinology, pediatric specialists, physicians referring patients to pediatric practitioners, general physicians, laboratory technicians in charge of mass screening, and patients.

Novel genetic variants in the TPO gene cause congenital hypothyroidism

BACKGROUND

Mutations in the dual oxidase maturation factor 2 (DUOXA2) and thyroid peroxidase (TPO) genes have been reported to cause goitrous congenital hypothyroidism (GCH). The aim of this study was to determine the genetic basis of GCH in affected children.

METHODS

Thirty children with GCH were enrolled for molecular analysis of the DUOXA2 and TPO genes. All subjects underwent clinical examination and laboratory testing. Genomic DNA was extracted from peripheral blood leukocytes, and Sanger sequencing was used to screen for DUOXA2 and TPO gene mutations in the exon fragments amplified from the extracted DNA. Family members of those patients with mutations were also enrolled and evaluated.

RESULTS

Analysis of the TPO gene revealed six genetic variants, including two novel heterozygous mutations, c.1970T> C (p.I657T) and c.2665G> T (p.G889X), and four mutations that have been reported previously (c.670_672del, c.2268dup, c.2266T> C and c.2647C> T). Three patients harbored the same mutation c.2268dup. The germline mutations from four unrelated families were consistent with an autosomal recessive inheritance pattern. Conversely, no mutations in the DUOXA2 gene were detected.

CONCLUSION

Two novel inactivating mutations (c.1970T> C and c.2665G> T) in the TPO gene were identified. The c.2268dup mutation occurred frequently. No mutations in the DUOXA2 gene were detected in this study.