The primary objective of this observational study is the evaluation of the quality of life and long-term outccome of young-adult patients with congenital hypothyroidism diagnosed by neonatal screening receiving replacement treatment with levothyroxine.

The secondary objective is to relate the results to the form of hypothyroidism, the initial dose of L-T4, treatment adherence and genetics

The study protocol will be performed in 3 different phases:

Step1:

A) Enrollment of patients meeting the following criteria:

• diagnosis of congenital hypothyroidism through neonatal screening adequately treated with L-T4
• confirmation of the diagnosis of hypothyroidism upon re-evaluation of the diagnosis
• age 16-21 years at the time of enrollment

B) Information interview on the study and signing of informed consent by the patient and/or parent/guardian

C) Retrospective collection of the following parameters at diagnosis:

• Values of TSH, FT4 at diagnosis, initial dose of L-T4
• Thyroid ultrasound and scintigraphy reports
• Genetic investigation report if available

D) Retrospective collection for each year of follow-up of:

weight, height, TSH, FT4 and L-T4 dose

Step 2:

A) Clinical evaluation (Weight, Height, BMI, Waist and hip circumference, blood pressure) B) Evaluation of body composition by performing bioimpedance analysis C) Evaluation of quality of life through administration of the SF36 test D) Evaluation of cognitive abilities through administration of the WAIS IV test E) Evaluation of any psychopathological conditions through the SCL-90 psychopathological screening questionnaire F) For patients up to 18 years of age: CBCL questionnaire administered to parents to describe the patient's behaviour

Step 3:

Data collection and analysis of results

Inclusion Criteria:

• Diagnosis of congenital hypothyroidism by neonatal screening
• Start of L-T4 therapy within the first month of life
• Confirmation of hypothyroidism condition upon reassessment of diagnosis

Exclusion Criteria:

• other chronic diseases and/or genetic syndromes
• family history of neuropsychiatric pathology
• familial dyslipidemia