Allan-Herndon-Dudley Syndrome: A Novel Pathogenic Variant of the SLC16A2 gene

Allan-Herndon-Dudley syndrome (AHDS) is a rare disorder characterized by thyroid irregularities, neurological issues, and developmental delay. In this article, we reported a patient with AHDS who presented with severe developmental delay and failure to thrive in the setting of thyroid irregularities. The patient had missense mutations in the SLC16A2 gene, which codes for monocarboxylate transporter 8 (MCT8). We identified two single-nucleotide variants, including guanine to alanine substitution at position +1 of intron 5 (IVS5+1 G>A) and guanine to alanine substitution at position 1400 of intron 1 (c.1400G>A). This variant has not been previously reported as pathogenic in a patient diagnosed with AHDS, as missense and in-frame single amino-acid deletions have not generally been associated with severe neurodevelopment sequela. We review the clinical and laboratory findings of this rare condition. We will discuss the value of early recognition and diagnosis based on promising clinical trials to treat the neurological and developmental sequela associated with AHDS.