The Severity of Congenital Hypothyroidism With Gland-In-Situ Predicts Molecular Yield by Targeted Next-Generation Sequencing

Abstract

Introduction: Congenital hypothyroidism with gland-in-situ (CH-GIS) is usually attributed to mutations in the genes involved in thyroid hormone production. The diagnostic yield of targeted next-generation sequencing (NGS) varied widely between studies. We hypothesized that the molecular yield of targeted NGS would depend on the severity of CH.

Methods: Targeted NGS was performed in 103 CH-GIS patients from the French national screening program referred to the Reference Center for Rare Thyroid Diseases of Angers University Hospital. The custom targeted NGS panel contained 48 genes. Cases were classified as solved or probably solved depending on the known inheritance of the gene, the classification of the variants according to the American College of Medical Genetics and Genomics, the familial segregation, and published functional studies. Thyroid-stimulating hormone at CH screening and at diagnosis (TSHsc and TSHdg) and free T4 at diagnosis (FT4dg) were recorded.

Results: NGS identified 95 variants in 10 genes in 73 of the 103 patients, resulting in 25 solved cases and 18 probably solved cases. They were mainly due to mutations in the TG (n = 20) and TPO (n = 15) genes. The molecular yield was, respectively, 73% and 25% if TSHsc was ≥ and < 80 mUI/L, 60% and 30% if TSHdg was ≥ and < 100 mUI/L, and 69% and 29% if FT4dg was ≤ and > 5 pmol/L.

Conclusion: NGS in patients with CH-GIS in France found a molecular explanation in 42% of the cases, increasing to 70% when TSHsc was ≥ 80 mUI/L or FT4dg was ≤ 5 pmol/L.

Keywords: congenital hypothyroidism; gland-in-situ; molecular yield; next-generation sequencing; severity.

Figure 1.

Classification of the cases, according to the genetic testing. See Supplementary Table S5 and Supplementary Table S6 and additional references (37) for a comprehensive classification of each case with variant descriptions. (A) Segregation of variants and CH in multiple affected family members. (B) The patient with NKX2-1 mutation had pulmonary involvement and neurological delay and a familial segregation of variant and CH. (C) Variants on 2 different genes were considered as partially unsolved because of the lack of evidence in the literature. ^t represents a patient with a transient form. Abbreviations: CH, congenital hypothyroidism.

Figure 2.

Proportion of genetic resolution according to the TSH level at neonatal screening (A) and at diagnosis (B), and the free T4 level at diagnosis (C) for all cases and only sporadic cases.