Prospective Evaluation of OptiThyDose

The aim of this multicentric, randomised, two-arms and single-blinded clinical trial is to prospectively evaluate OptiThyDose for Congenital hypothyroidism (CH) and Graves' disease (GD).

Inclusion Criteria: Congenital hypothyroidism (CH) * Newborns with pathological neonatal screening and confirmation of an increased Thyrotropin (TSH) level in an independent venous blood sample Graves' disease (GD) * Children until 18 years with new diagnosis of GD, recurrence of GD, or insufficiently controlled GD under CMZ/MMZ during follow-up according to: * Pathological lab values (suppressed TSH, increased thyroid hormone levels, positive Anti-TSH-receptor antibodies) * Typical clinical picture, if present (goitre, tachycardia, palpitations, weight loss, hyperphagia, altered mood) CH and GD * The study participant must be accessible for scheduled visits, treatment and follow-up. * Signed Informed Consent form (ICF) obtained prior to any study related procedure. Written IC for study participation must be signed and dated by the patient and/or his/her legal representative(s) in accordance with national legal requirements Exclusion Criteria: CH and GD * Exclusion of newborns from mothers with GD * Exclusion of patients in case of a life-threatening event GD * Exclusion of children with known other aetiologies of hyperthyroidism than GD without elevated Anti-TSH-receptor antibodies e.g.: * known toxic thyroid nodules proven by ultrasound/scintigraphy * known amiodarone induced hyperthyroidism * known McCune Albright syndrome (based on clinical, laboratory, and genetic diagnosis) associated hyperthyroidism * known genetically proven hyperthyroidism caused by activating mutations of the TSH receptor gene