ESPE Abstracts

Background: Monocarboxylate transporter 8 (MCT8) is a specific transporter of triiodothyronine (T₃). MCT8 gene mutations cause a rare X-linked disorder known as Allan–Herndon–Dudley syndrome, characterized by thyroid dysfunction (high T₃, low T₄, and normal/high TSH) and psychomotor retardation.

Case report: A 4-year- and 9-month-old boy, who was already having L-T₄ treatment for hypothyroidism was admitted to our coutpatient clinic. He was also under supervision of paediatric neurology because of congenital hydrocephaly, cerebral palsy and epilepsy. Neuromotor development was severely retarded and complete blindness was present. The parents were non-consanguineous, his uncle and cousin also had similar neuromotor deficits and epilepsy. Physical examination revealed severe hypertonia of limbs and exaggerated deep tendon reflexes. The weight was 18.7 kg (50 p), the height was 106 cm (10–25 p), the head circumference was 47 cm (3–10 p, −1.29 SDS), thyroid gland was non-palpable and unilateral cryptorchidism was present. Thyroid hormone levels, under 100 μg/day L-T₄ treatment, were as follows: fT₃: 5.76 pg/ml (1.7–3.71), fT₄: 0.62 ng/dl (0.8–2.2), and TSH: 0.8 mUI/l (0.4–4). Thyroid hormones of his 2-year- and 9-month-old male cousin were as follows: fT₃: 5.41 pg/ml (1.7–3.71), fT₄: 0.7 ng/dl (0.89–1.76), and TSH: 5.5 mUI/l (0.4–4). Allan–Herndon–Dudley syndrome was confirmed by a deletion of 1683rd nucleotide of exon 6 of MCT8 gene.

Conclusion: In case of low fT₄ levels in association with severe neurologic findings, MCT8 deficiency should be considered and fT₃ measurement should be performed.