ESPE Abstracts

Background: Variety of defective thyroid hormone biosynthesis accounts for 15% of congenital hypothyroidism. Children with IYD gene (formerly DEHALI) mutation, which encodes thyroidal enzyme iodotyrosine deiodinase, cannot recycle iodine in thyroid gland. This results in urinary loss of iodine and hypothyroidism. The condition may be missed by neonatal screening programs.

Case description: A male baby was born of non-consanguineous Asian parents at 33 weeks of gestation. He has had normal neonatal screening test. Hypothyroidism was diagnosed at 2 months of life with TSH of 340 pmol/l and free T4 of 4.0 pmol/l. Thyroid Isotope scan demonstrated normally situated bulky thyroid gland with intensely avid uptake of radioisotope. Thyroglobulin level was 1061 mg/l, and Thyroglobulin antibody was negative. His urine iodine:creatinine ratio was very high (2361.19 nmol/mmol, reference range 50-360 nmol/mmol) without antenatal or postnatal iodine exposure. Attempted breast milk iodine quantification was unsuccessful. His plasma iodine and mother’s thyroid function were within normal limits. Exome sequencing did not identify de novo or autosomal/X-linked recessive pathogenic variant(s). The boy is currently 7 years old and needs only a small dose of thyroxine to be euthyroid. In addition, he has unexplained tachypnoea since birth and developmental delay.

Discussion: In the evaluation of dyshormonogenesis, urine iodine excretion is a valuable test to narrow down the diagnosis of IYD gene mutation. The diagnosis of mild thyroidal dyshormonogenesis is unlikely to explain the association with persistent unexplained tachypnoea and developmental delay but this is the first reported case of such associations.