RESUMEN
INTRODUCTION: Allan-Herndon-Dudley Syndrome (AHDS) is a rare X-linked recessive intellectual disability condition with neuromuscular involvements. Altered thyroid function tests are major milestones in AHDS diagnosis. However, due to phenotypic variations in the levels of thyroid hormones in AHDS patients, we believe that the disorder is often underdiagnosed. Here, we reported a 3.5-year-old boy with an AHDS diagnosis and healthy thyroid hormones. METHODS: Whole-Exome sequencing followed by data analysis was performed on the patient's sample. The mutation was confirmed by Sanger sequencing in the patient and his mother. RESULTS: We reported a 3.5-year-old boy with AHDS diagnosis and a novel synonymous missense mutation (c. 1026G>A) in the SLC16A2 gene manifesting normal levels of T3, T4, and TSH. The mutation causes no change in amino acid sequence; however, it affects splicing through alteration of an exonic splicing enhancer. To the best of our knowledge, there are only 3 similar reports in the literature reporting AHDS diagnosis and normal levels of thyroid hormones. CONCLUSION: The altered levels of thyroid hormones are notable but not necessary markers for diagnosing AHDS. The candidate diagnosis of AHDS should be considered in patients with X-linked recessive intellectual disability syndrome with neuromuscular involvements irrespective of levels of thyroid hormones; otherwise, it could lead to the under-diagnosis of the disorder.