Congenital hypothyroidism (CHT) results from an absent or underdeveloped thyroid gland (dysgenesis), or the gland has developed but cannot produce enough thyroid hormone (dyshormonogenesis
Approximately 15-20% of CH cases result from thyroid dyshormonogenesis
(DH) caused by mutations in thyroid hormone synthesis pathway genes, including those involved in hormone precursor production (thyroglobulin (TG)) , iodine transportation across the basal membrane (solute carrier family 5 member 5 (SLC5A5) , solute carrier family 26 member 4 (SLC26A4) ), thyroglobulin modification (thyroid peroxidase (TPO) , dual oxidase 2 gene (DUOX2) , and dual oxidase maturation factor 2 (DUOXA2) ), and iodine recycling in the thyroid (iodotyrosine deiodinase (IYD)) .
In the presence of fetal goiter in a euthyroid mother and CH, we suspected of dyshormonogenesis
, which was confirmed by genetic studies that revealed two heterozygous and pathogenic variants in the TPO gene.
There were 23 cases (14F, 9M) in permanent primary congenital hypothyroidism group and 12 (52.2%) of them were dysgenesis (8 hypoplasia, 4 ectopia), and 11 (47.8%) dyshormonogenesis
. In transient primary congenital hypothyroidism group, there were 25 cases (17M, 8F).
Of the 31 patients with CH, 14 were cases of hypoplastic thyroid gland, one had agenesis, one had an ectopic thyroid gland, 14 had thyroid dyshormonogenesis
, and one had a fetal goiter related to the TPO gene mutation.
Changes in TG are more commonly associated with dyshormonogenesis
, occurring with a frequency of 25%.
Iodine deficiency is the most common cause of HT, but congenital HT and autoimmune HT are other varieties with different genetic causes  that cause central HT, primary HT, alterations in thyroid transcription factors (with which the FOXE1 gene is associated), dyshormonogenesis
, and other genes such as the TG and TSH genes .
Hypothyroidism, abnormalities in thyroid hormone synthesis or thyroid dyshormonogenesis
, is a common endocrine disorder  involved with multiple organs.
Analytical interference in TSH or fT4 immunoassay, congenital hypothyroidism secondary to dyshormonogenesis
, and consumptive hypothyroidism due to hemangioendothelioma are the possible causes for discrepant TSH and fT4 results in this patient.
The commonest etiologies are thyroid dysgenesis (aplasia, hypoplasiaand ectopics) and dyshormonogenesis
. Thyrotropin receptor blocking antibodies, maternal medications, iodine deficiency, genetic mutations are other causes.
Increased pertechnetate uptake is rarely seen in the gland, in keeping with dyshormonogenesis
, which has a higher hereditary incidence.