Contribution of genetic factors to neonatal transient hypothyroidism

The role of initial clinical and laboratory findings in infants with hyperthyrotropinemia to predict transient or permanent hypothyroidism

OBJECTIVE

Studies on the clinical course of children with hyperthyrotropinemia are scarce. We aimed to evaluate the role of presentation findings in such infants to predict eventual outcome.

METHODS

Files of infants diagnosed as suspicious congenital hypothyroidism (CH) in the neonatal or early infancy period in the past ten years were analyzed retrospectively, and 37 patients (M/F: 20/17) with hyperthyrotropinemia diagnosed at a median age of 3.2 months were included in the study. Criteria for inclusion were: normal free thyroxine (fT4) levels and thyrotropin (TSH) levels between 10-20 μIU/mL during the initial neonatal screening (or TSH<10μIU/mL afterwards). Cases with permanent CH (Group 1) were compared to those with transient hyperthyrotropinemia (Group 2) regarding age at the time of diagnosis, sex, gestational age, birth weight, symptoms, ultrasonographic and scintigraphic findings, initial thyroid function tests, and state of mental and motor development.

RESULTS

Of the total group, 20 patients (54%) were eventually diagnosed as permanent CH. T4 doses that maintained normal thyroid function tests were significantly higher at the end of the first and second years of life in this group. Age, TSH and fT4 levels at the time of diagnosis, sex, gestational age, birth weight, symptoms, ultrasonographic and scintigraphic findings, and the state of mental and motor development were similar in the two groups.

CONCLUSIONS

T4 dose required to maintain a euthyroid state was the only parameter which distinguished between transient and permanent CH.

Genetic causes of congenital hypothyroidism due to dyshormonogenesis

PURPOSE OF REVIEW

Overview of congenital hypothyroidism caused by thyroid hormone synthesis defects, the current understanding of their pathophysiology, and clinical implications of molecular diagnoses.

RECENT FINDINGS

Genetic defects in all known thyroid-specific factors required for thyroid hormone synthesis have been described. These include defects in iodide trapping (NIS), in the facilitated iodide efflux across the apical membrane (PDS), the organification of iodide within the follicular lumen (thyroid peroxidase, DUOX2, DUOXA2), the substrate for thyroid hormone synthesis (thyroglobulin) and the ability to recover and retain intrathyroidal iodine (iodotyrosine deiodinase). Clinical and biochemical evaluation aids in selecting the most appropriate candidate gene(s). A definite molecular diagnosis of thyroid dyshormonogenesis allows genetic counseling and has prognostic value in differentiating transient from permanent congenital hypothyroidism and predicting the response of patients to iodine supplementation as adjunct or alternative treatment to L-T4 replacement.

SUMMARY

Congenital hypothyroidism due to thyroid dyshormonogenesis is a heterogenic disorder that may be caused by mutations in any of the known steps in the thyroid hormone biosynthesis pathway. An exact molecular diagnosis allows genetic counseling and the identification of asymptomatic mutation carriers at risk of recurrent hypothyroidism, and provides a rationale for adjunct iodide supplementation.

Update: newborn screening for endocrinopathies

Congenital hypothyroidism and congenital adrenal hyperplasia are included in many newborn screening (NBS) panels worldwide and in all state-sponsored programs in the United States. Both conditions meet the fundamental prerequisites for NBS: high incidence in the population; biomarkers in the dried blood specimen that are easily detected; and, effective therapies to lessen, if not prevent, the sequelae of late or no treatment. In this review, the history of NBS is discussed for these 2 conditions. The technologies and protocols used in their detection, and related subjects such as genetics, and treatment and outcomes, are also discussed.

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

About 30% of children with elevated TSH levels during neonatal screening have a transient form of disorder. On the other hand, it has been reported that subclinical hypothyroidism persists in late childhood in about 30% of children found to be false-positive during neonatal screening. The aim of this study was to determine whether transient thyroid dysfunction and subclinical hypothyroidism detected during neonatal screening are influenced by genetic background. The TSH receptor (TSHR), thyroid peroxidase (TPO) and dual oxidase 2 (DUOX2) genes, for which it has been reported that heterozygous defects cause neonatal transient thyroid dysfunction, were analyzed. Nine children with transient thyroid dysfunction or subclinical hypothyroidism detected during neonatal screening were studied. One child was heterozygous for a TSHR gene mutation (R450H), and another child was heterozygous for a TPO gene mutation (P883S). No children with mutation of the DUOX2 gene were identified. Genetic background may contribute to development of transient thyroid dysfunction and subclinical hypothyroidism detected during neonatal screening.