Evaluation of genetic etiology with a new generation sequence analysis in congenital hypothrody patients with dishormonogenesis

Hypothyroidism is defined as insufficient thyroid hormone production by the thyroid gland due to any problem in the hypothalamus-pituitary-thyroid gland axis. It can be congenital or acquired. Congenital hypothyroidism is the most common endocrine disorder in the neonatal period and is one of the most important causes of preventable mental retardation. It can be seen as temporary (40-50%) or permanent (50-60%). Iodine deficiency or excess is among the causes of transient hypothyroidism due to maternal autoimmune thyroid diseases, maternal antithyroid drug use, or some drugs used in the neonatal period. Permanent hypothyroidism can be seen due to dysgenesis of the thyroid gland (60%) or dyshormonogenesis (40%), secondary or central hypothyroidism due to hypothalamo-hypophyseal causes, and transport/metabolism defects of thyroid hormones. The incidence of congenital hypothyroidism is known as 1/4000, but there are publications showing an increase in its incidence in recent years, and its current incidence has been reported as 1/2000. The etiology of the increase in the number of cases is not known exactly. Reasons such as endocrine disrupting agents, lowering of the TSH threshold value used in the hypothyroidism screening test, and access to more people by medical services are thought to be the reasons for this increase. Etiologically, there was no increase in the frequency of dysgenesis and severe hypothyroidism when compared to previous years; It has been determined that there is an increase in cases related to dyshormonogenesis or with mild-transient course. The frequency of dyshormonogenesis has been reported to be between 15-40% in patients with congenital hypothyroidism and it is thought to increase . Dyshormonogenesis-induced hypothyroidism, which is one of the causes of primary congenital hypothyroidism, is frequently seen in autosomal recessive inheritance as a result of mutations in the genes encoding the receptors or enzymes involved in the thyroid hormone synthesis steps. The thyroid gland is eutopically located (normally), often of normal size or slightly enlarged (goiter). Sodium/iodide symporter (NIS or SLC5A5), thyroperoxidase (TPO), thyroglobulin (TG), dual oxidase 2 and its receptor (DUOX2 and DUOXA2), pendrin (SLC26A4 or PDS), IYD/DEHAL1 and SLC26A7 have been reported as genes responsible for the etiology . As a result of the development of technology, new methods such as comparative genetic hybridization (CGH), next generation sequencing (targeted NGS) and whole exome sequencing (WES) have enabled large population studies in cases with congenital hypothyroidism. showed an oligogenic inheritance pattern. Although the number of genes associated with congenital hypothyroidism is increasing, the exact extent of congenital hypothyroidism attributable to known genetic causes and the relative prevalence of mutations in specific genes is not known with certainty, and results vary between studies. For example, DUOX2, which seems to be the most responsible gene in East Asian populations in studies, has been reported with a frequency of 16-32% in congenital hypothyroidism patients and 18% in a group of European and Middle Eastern patients in Korea, Japan and China. These differences may be due to the ethnic origin of the cohort and the choice of congenital hypothyroidism type (dysgenesis/dyshormonogenesis) studied . In our country, the frequency of consanguineous marriages and the autosomal recessive inheritance pattern may have contributed to a different genetic spectrum than is known in the dyshormonogenesis-related hypothyroidism group . We have limited national data on the genetic etiology of hypothyroidism due to dyshormonogenesis. Congenital hypothyroidism due to dyshormonogenesis with a mild clinical course is thought to be responsible for the increasing cases of congenital hypothyroidism. The reason for this increase is not fully known. The prevalence and clinical course of dyshormonogenesis are not known precisely due to the type of congenital hypothyroidism studied and the selection of cohorts differing in ethnicity. The aim of this study is to elucidate the molecular cause using next generation sequencing in a well-characterized cohort of dyshormonogenetic congenital hypothyroidism patients. In our study, pediatric patients who were thought to have hypothyroidism due to dyshormonogenesis were included. Thyroid dysgenesis (ectopia, agenesis, hypoplasia, hemiagenesis) was excluded by imaging methods and patients with one of the following criteria were included in the study; 1. First degree relatives (mother, father or sibling) diagnosed with congenital hypothyroidism 2. Having a history of consanguinity between parents 3. L-thyroxine treatment cut will be tried and patients with TSH value ≥10 IU/mL in the control will be taken. 4. Patients with a diagnosis of subclinical hypothyroidism who continue to have TSH values of >10 IU/L while not receiving treatment. 5. Those who are over three years old and L-thyroxine requirement is >2μg/kg/day. 6. Those with the diagnosis of congenital hypothyroidism and goiter. Using the next generation sequencing (NGS) method from patients, GLIS3, TSHB, THRA, THRB, PAX8, NKX2-5, NKX2-1, FOXE1, TSHR, SLC5A5, SLC26A4, TG, TPO, DUOX2, DUOXA2, IYD, SLC26A7, 7DUOX1, ZNF60 A panel screen of the genes, SLC6A4, DIO1, DIO2, DIO3, TTR, GNAS, TRH, ALB, POR, TRHR, PHEX, SLC16A2, SERPINA7, IGSF1 was performed. Conclusion; Fifty nine patients were included in the study. A total of 31 patient (52.5%) were detected to have a variant. Independent of oligogenic inheritance, the TSHR was the most common variant detected gene in our cohort (16/32).The second most common gene was TG (8/32) and the other genes were TPO (6/32) SLC26A4 (3/32) , DUOX2( 2/32) THRB (1/32), DUOX1 (1/32) DUOXA2 (1/32). Six cases had oligogenic inheritance (TSHR-DUOXA2, TSHR-TG, SLC26A4-TG, TG-TPO, DUOX2-TSHR). One case had a biallelic variant in the TSHR gene. Monoallelic variants were detected in TSHR, TPO, DUOX1, DUOX2, THRB, SLC26A4 and TG in 22 patients (71%). Five novel variants were identified. The data that obtained as a result of this study may contribute to the development of diagnosis, treatment and follow-up protocols in the future since they have congenital hypothyroidism due to dyshormonogenesis; It will be a guide for possible gene therapy. This data will also be important in prenatal and postnatal genetic counseling that can be given to future generations.