The Allan–Herndon–Dudley syndrome (AHDS; MIM 300523) of X-linked mental retardation and hypotonia is caused by mutations in a thyroid hormone transporter gene—the monocarboxylate transporter 8 (MCT8 also known as SLC16A2) gene. A 23-month-old boy with severe developmental delay, hypotonia, recurrent emesis, and irritability is described. He was diagnosed with hypothyroidism at the age of 4 months. However, T3 level was elevated. Molecular analysis of the MCT8 gene detected a single base duplication in exon 5 c.1614dupC (p.Ile539fs), consistent with a diagnosis of AHDS. While T3 is the best marker for this disorder, elevations in TSH should alert to the diagnosis.
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Thyroid stimulating hormone
- MCT 8 :
Monocarboxylate transporter 8
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Conflict of interest
There is no conflict of interest. No funding was required for this study.
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Crushell, E., Reardon, W. Elevated TSH levels in a mentally retarded boy. Eur J Pediatr 169, 573–575 (2010). https://doi.org/10.1007/s00431-009-1075-0
- Allan–Herndon–Dudley syndrome
- X-linked mental retardation
- MCT 8