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Patients and Caregivers | Healthcare Professionals
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A young boy with MCT8 deficiency.

TURN UP THE VOLUME

on MCT8 deficiency diagnosis

TURN UP THE VOLUME on MCT8 deficiency diagnosis

Increase your awareness of MCT8 deficiency. See why including T3 in a thyroid hormone panel is necessary for diagnosis.1

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Increase your awareness of MCT8 deficiency. See why including T3 in a thyroid hormone panel is necessary for diagnosis.1

LEARN MORE
A young boy with MCT8 deficiency and the male symbol.

MCT8 DEFICIENCY IS RARE BUT DEVASTATING2

CHILDHOOD MORTALITY

1 in 3 affected die in childhood1,a

aMedian overall survival was 35 years in a large natural history study of individuals with MCT8 deficiency.3

MCT8 deficiency (Allan-Herndon-Dudley syndrome [AHDS]) causes severe neurodevelopmental impairment due to thyroid hormone not entering the brain during critical periods of its development.2 Simultaneously, excess peripheral T3 drives persistent thyrotoxicosis with multisystem complications.2 Clinical manifestations become evident at 2 to 3 months of age.1

Although intervention cannot reverse the underlying neurolodevelopmental impairment, early diagnosis can support management and help patients and caregivers address daily challenges.1

REVIEW CLINICAL IMPACT
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There’s a Significant Time-to-Diagnosis Delay4

ONSET OF SYMPTOMS

2 to 3 months1

MEDIAN TIME TO DIAGNOSIS

14 months (range: 0 months-26 years)4

MCT8 deficiency often shows signs very early in life, but diagnosis is frequently delayed.1,4

For children born after 2017, this delay in diagnosis has shortened to roughly 8 months, largely due to increased awareness and wider use of genetic testing—but significant delays still occur.5

LEARN MORE ABOUT DIAGNOSIS CHALLENGES
Doctor and patient discussing testing results.

The Importance of a Timely Diagnosis

IDENTIFY THE THYROID HORMONE PANEL PROFILE1

High T3

Low/low-normal free T4

Normal to mildly elevated TSH

Patients with MCT8 deficiency exhibit multisystem involvement well before diagnosis. Physicians should suspect MCT8 deficiency in patients with1,2,5:

  • Neurodevelopmental impairment
  • Hypotonia
  • Dystonia
  • Progressive deterioration in body weight
  • Tachycardia
  • Abnormal blood pressure
  • Notable feeding problems
REVIEW TESTING PROCESS

STANDARD THYROID HORMONE PANELS DO NOT INCLUDE T3. ADDING T3 TESTING1:

  1. Is critical for earlier diagnosis of MCT8 deficiency
  2. Can trigger earlier confirmatory genetic testing
  3. May improve overall management of the disorder
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EXPAND YOUR MCT8 DEFICIENCY KNOWLEDGE

Explore additional MCT8 deficiency resources, and see a listing of relevant 2026 professional events to learn more about MCT8 deficiency.

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References: 1. Bauer AJ, Auble B, Clark AL, et al. Unmet patient needs in monocarboxylate transporter 8 (MCT8) deficiency: a review. Front Pediatr. 2024:12:1444919. 2. van Geest FS, Gunhanlar N, Groeneweg S, Visser WE. Monocarboxylate transporter 8 deficiency: from pathophysiological understanding to therapy development. Front Endocrinol (Lausanne). 2021:12:723750. 3. Groeneweg S, van Geest FS, Abacı A, et al. Disease characteristics of MCT8 deficiency: an international, retrospective, multicentre cohort study. Lancet Diabetes Endocrinol. 2020;8(7):594-605. 4. van Geest FS, Groeneweg S, Popa VM, Stals MAM, Visser WE. Parent perspectives on complex needs in patients with MCT8 deficiency: an international, prospective, registry study. J Clin Endocrinol Metab. 2024;109(1):e330–e335. 5. Groeneweg S, van Geest FS, Peeters RP, Heuer H, Visser WE. Thyroid hormone transporters. Endocr Rev. 2020;41(2):146-201.